Macrophages are crucial components of the innate immune system. They can be classified into two categories: those derived from monocytes and those derived from tissue-resident macrophages (TRMs).

Generally, monocytes originate from the bone marrow. In the bone marrow, monocyte development includes the following progenitor cells: common myeloid progenitors (CMPs), granulocyte–macrophage progenitors (GMPs), and monocyte–macrophage and dendritic cell (DC) precursors (MDPs) (14). MDPs can differentiate into common monocyte progenitors (cMoPs), which may give rise to monocyte precursors. These precursors then develop into Ly6C^hi monocytes, migrate from the bone marrow and circulate in the blood, and after a few days, they enter tissues and differentiate into macrophages (15). Monocyte-derived macrophages play a key role in clearing pathogens and cellular debris, antigen presentation, and initiating adaptive immune responses (16).

TRMs typically enter organs during embryonic or early postnatal development and exist largely independently of monocyte input throughout life (17). Many TRM populations (in the heart, lungs, liver, kidneys, and brain) originate from fetal liver or yolk sac progenitors (15, 18). There are also populations of TRMs (in the stomach, intestine, and colon) that originate from peripheral monocytes and are subsequently maintained through local proliferation (19, 20). TRMs are often replenished by monocytes, especially in infection or injury. During inflammatory disease, the initiation of inflammation in different tissues leads to a rapid decline in TRMs (21). At this time, inflammatory monocytes/macrophages are recruited to the site of inflammation, where they play an important role in immune defense but may also contribute to the pathogenesis of various inflammatory diseases and organ failure (22). In acute lung injury, peripheral blood monocytes can differentiate into interstitial macrophages and alveolar macrophages, and interstitial macrophages can further differentiate into alveolar macrophages (23). TRMs acquire unique functions on the basis of the organs in which they reside (24). In basal states, TRMs are considered functionally immunosuppressive; they play important roles in maintaining homeostasis, inhibiting T cell activation, and promoting the resolution of inflammation (25). However, in inflammatory or pathological conditions, the functions of TRMs can be altered significantly. For example, in the tumor microenvironment, TRMs can be reprogrammed to exhibit pro-tumorigenic effects by promoting angiogenesis and tumor invasion (26, 27). During inflammation, Alveolar macrophages have also been shown to initiate inflammation by secreting C-X-C Motif Chemokine Ligand 1 (CXCL1), which enhances the recruitment of neutrophils (21).

Monocyte-derived macrophages differentiate into different phenotypes on the basis of various environmental stimuli, with the most classic classification being M1 and M2 macrophages (28). In addition to the classic classification, Mreg macrophages are another newly identified type (29) (Table 1).

M1 macrophages arise in response to activation by pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs), and proinflammatory cytokines (such as interferon-γ, IFN-γ and tumor necrosis factor, TNF) (30). Following LPS activation, Fcγ receptor-mediated phagocytosis and Mitogen-Activated Protein Kinase (MAPK), Janus Kinase 1(JAK1), and JAK3 signaling are activated in M1 macrophages (31). These pathways control several inflammatory genes, endowing macrophages with proinflammatory characteristics (32, 33). M1 macrophages play crucial roles in defending against pathogens and initiating inflammatory responses. These cells express markers such as Cluster of Differentiation 86 (CD86), CD68, MHC class II molecules, and inducible nitric oxide synthase (iNOS). Moreover, they secrete high levels of proinflammatory cytokines, including interleukin-1β (IL-1β), IL-6, IL-12, IL-23, and TNF-α, thereby promoting inflammation and cytotoxicity (34). M1 macrophages can produce abundant reactive oxygen species (ROS) and reactive nitrogen species (RNS) to combat pathogen invasion. Concurrently, they secrete proinflammatory cytokines and stimulate the polarization of T helper 1 (Th1) cells, resulting in robust inflammation (35). However, the excessive proinflammatory and cytotoxic actions of these macrophages can lead to severe tissue damage (36).

In contrast to M1 macrophages, M2 macrophages play a central role in tissue repair, immune regulation, and fibrosis (37). These cells are typically activated by cytokines secreted by T helper 2 (Th2) cells and exhibit reduced antigen-presenting capabilities along with elevated levels of anti-inflammatory cytokines, such as IL-10 and transforming growth factor-β (TGF-β) (38). This anti-inflammatory effect helps to balance excessive inflammatory responses. However, the overactivation of M2-like macrophages can lead to tissue fibrosis, potentially resulting in organ dysfunction (35). M2 macrophages can be divided into four subtypes, M2a, M2b, M2c, and M2d macrophages, each with distinct functions (28, 39). M2a macrophages are induced by IL-4 and IL-13, M2b macrophages are activated by IL-1R or TLR agonists, M2c macrophages are induced by IL-10 and glucocorticoids, and M2d macrophages are induced by A2 adenosine receptors (A2Rs) and IL-6 (28).

M2a macrophages express high levels of the mannose receptor (CD206) and secrete profibrotic factors, such as TGF-β, which promote tissue repair (12). M2a macrophages can activate the STAT6 pathway through the coreceptor IL-4Rα, a pathway that primarily mediates tissue repair and antifungal responses, inducing the production of arginase 1 (Arg 1). Following this, arginine is degraded into polyamines and proline. These byproducts increase cell division and the accumulation of collagen fibers, which are vital processes for the repair and regeneration of tissues (35).

M2b macrophages are phenotypically and functionally similar to Mregs and are capable of producing both proinflammatory and anti-inflammatory cytokines, such as TNF-α, IL-1β, IL-6, and IL-10 (12, 40). In lupus nephritis, Granulin (GRN) enhances M2b polarization, leading to increased release of pro-inflammatory factors, which in turn worsens kidney inflammation and fibrosis (41). However, in the myocardial ischemia-reperfusion injury model, α-lipoic acid (ALA) induces M2b polarization, reducing inflammatory damage to cardiomyocytes and promoting IL-10-mediated immune tolerance. This will improve heart function (42).

M2c macrophages, also known as deactivated macrophages, possess anti-inflammatory functions. They secrete IL-10 and TGF-β and effectively phagocytose and eliminate apoptotic cells (28). Recent studies reveal that peroxisome proliferator-activated receptor γ (PPARγ)-dependent lipid synthesis is crucial for their repair functions—dephosphorylation of PPARγ T166 enhances fatty acid metabolism, fueling the production of PDGF, TGF-β, and VEGF to support tissue regeneration in skin and liver injuries (43).

M2d macrophages exhibit phenotypic and functional resemblance to tumor-associated macrophages (TAMs) (35). They secrete IL-10, TGF-β, and vascular endothelial growth factor (VEGF), promoting angiogenesis and tumor metastasis (44). For example, in gastric cancer, M2d macrophages can secrete these cytokines to promote tumor proliferation and metastasis (44, 45).

Mregs, a special subtype, are primarily formed through the differentiation of bone marrow precursors and peripheral blood mononuclear cells in in vivo microenvironments under special circumstances (35). Dehydrogenase/Reductase Member 9 (DHRS9) is a unique and stable marker of Mregs (46). Mregs possess distinct immunosuppressive functions (47) and play a key role in immune responses, especially during the process of tissue damage repair. A notable characteristic of Mregs is their high expression of MHC-II and CD80 molecules, which not only endows them with potent immunosuppressive capabilities but also enables them to effectively present antigens (46). Mregs can suppress immune responses both directly and indirectly. They can directly inhibit the proliferation of activated allogeneic and xenogeneic T lymphocytes and can also indirectly suppress immune responses by inducing regulatory T cells (Tregs) or by secreting molecules such as IL-10, TGF-β, NOS, and Indoleamine 2,3-Dioxygenase (IDO) (28, 35, 47).

Unlike monocyte-derived macrophages, TRMs present distinct phenotypes under homeostatic conditions. TRMs are characterized primarily by the expression of different markers according to specific phenotypes; monocyte-derived macrophages are characterized by the expression of CD11b, CD209, CD64, and c-mer tyrosine kinase (MerTK) (47). TRMs are divided into different subpopulations, such as Kupffer cells in the liver, alveolar macrophages in the lungs, microglia in the brain, and macrophages in the heart, on the basis of their anatomical location and function (37). TRM is a complex cell population. The current definition of TRM is not complete, and markers vary across different organs. For example, kupffer cells in the liver highly express inhibitor of DNA binding 3 (ID3) and Dectin1; alveolar macrophages express CD11c, sialic acid-binding Ig-like lectin F (Siglec-F) (in mice) or CD169 (in humans); and microglia express purinergic receptor P2Y, G-protein coupled, 12 (P2RY12) and transmembrane protein 119 (TMEM119) (48–50). Therefore, further researches are needed to provide accurate clues. Studies show that TRMs can also polarize according to their functions. For instance, alveolar macrophages can be categorized into two groups: M1 macrophages, which are characterized by pro-inflammatory and profibrotic activities and actively recruit neutrophils, and M2 macrophages, which exhibit anti-inflammatory and anti-fibrotic properties, promote asthma development, and facilitate tissue regeneration and resolution of inflammation (21). Microglia in the M1 polarization state exhibit strong pro-inflammatory and phagocytic functions, whereas in the M2 polarization state, they possess anti-inflammatory and tissue repair functions (51).

In human and murine atherosclerotic lesions, other types of macrophages have been identified, such as M4, Mox, Mhem, and M(Hb) macrophages (12). M4 macrophages, which are induced by the platelet chemokine CXCL-4, primarily express CD68, the calcium-binding protein S100A8, and matrix metalloproteinase (MMP) 7 in the adventitia and intima of arteries, and they are associated mainly with plaque instability (52). Mox macrophages have been identified in the atherosclerotic plaques of mice, where they are induced by oxidized phospholipids (oxPL). Mox macrophages account for up to 30 % of total plaque macrophages, and their specific functions remain to be further investigated (53). M(Hb) and Mhem macrophages are two subtypes of macrophages found in atherosclerotic plaques that coexist at sites of neovascular bleeding or unstable plaques (54). M(Hb) macrophages, which are stimulated by hemoglobin, typically express high levels of mannose and CD163 receptors and are involved in the clearance of hemoglobin/haptoglobin (Hb/Hp) complexes after plaque hemorrhage (55). After Hb/Hp complexes and erythrocytes are engulfed, the released heme can shift macrophages toward the Mhem phenotype (56). This particular subtype is capable of inhibiting the development of foam cells and offers specific protective benefits against atherosclerosis (57).

Mitochondria are crucial for the viability of eukaryotic cells, as they play important roles in bioenergetics, metabolism, and signaling (96). Many studies have focused on the impact of mitochondrial function and biogenesis on macrophages.

Mitochondrial fusion and fission can regulate macrophage polarization and function. Ganglioside-induced differentiation-associated protein 1 (GDAP1L1) phosphorylates dynamin-related protein 1 (Drp1), promoting its translocation from the cytosol to mitochondria, leading to mitochondrial fission. This will promote the M1 macrophage polarization. Consequently, the production of cytokines and chemokines is augmented via the MAPK and NF-κB pathways, leading to psoriasis inflammation (97). In contrast, MFN-mediated normal mitochondrial fusion could promote the M2 macrophage phenotype and inhibit the M1 phenotype. According to the study by Li et al. (98), Xuanfei Baidu Formula (XBF) alleviates casp11-dependent NLRP3 inflammasome activation through promoting MFN1-induced mitochondrial fusion, which prevent macrophage polarization to the M1 pro-inflammatory phenotype.

Mitochondrial biogenesis can also regulate macrophage polarization and function. Research indicates that γ-amino butyric acid (GABA) suppresses α-ketoglutarate dehydrogenase (OGDH) activity, lowering succinyl-CoA (SCOA) levels. This reduction diminishes mitochondrial protein succinylation, thereby boosting oxidative phosphorylation efficiency and promoting M2 macrophage polarization (99). Olfactomedin-like protein 3 (OLFML3) protein enhances M2 polarization by promoting immune-responsive gene 1 (IRG1) mitochondrial localization, catalyzing itaconate production, which maintaining mitochondrial membrane potential and mitochondrial reactive oxygen species (mtROS) homeostasis (100). During chronic kidney disease (CKD), the AMPK signaling pathway is inhibited, which result in mitochondrial biogenesis (nuclear respiratory factor 1 and mitochondrial transcription factor A) as well as mitochondrial-specific proteins (cytochrome C and mitochondrial complex IV) downregulated, leading to M1 polarization of macrophages (101).

Sirtuins (SIRT), initially identified in yeast as the first nicotinamide adenine dinucleotide (NAD)⁺-dependent epigenetic and metabolic regulators, belong to the class III histone deacetylases. Their activity relies on the presence of NAD⁺ (124). The sirtuins protein family primarily comprises seven members. SIRT1, SIRT6, and SIRT7 are typically localized in the nucleus, where they are involved in chromosomal stability and transcriptional regulation; SIRT2 is mainly found in the cytoplasm but can also be present in the nucleus; SIRT3, SIRT4, and SIRT5 are usually located in the mitochondria, where they regulate metabolic enzymes and stress response mechanisms (125). The substrates of nuclear sirtuins include histones and non-histone proteins, such as nuclear transcription factors and cofactors. In contrast, cytoplasmic and mitochondrial sirtuins play crucial roles in key enzymes involved in oxidative and metabolic pathways, including glycolysis, fatty acid oxidation, and the TCA cycle (126).

Sirtuins influence macrophage polarization through multiple pathways. SIRT1/2 can directly inhibit the NF-κB signaling pathway by deacetylating the p65 subunit of NF-κB, reducing the expression of pro-inflammatory cytokines (such as IL-6, IL-1β, and TNF-α) and suppressing M1 polarization (127–129). SIRT1 can also upregulate the expression of STAT6 to promote M2 polarization (130). SIRT3 promotes M2 polarization by activating mitochondrial autophagy, which reduces the release of inflammatory cytokines like IL-1β and TNF-α (131, 132). SIRT4 decreases M1 polarization by inhibiting STAT3 and suppressing inflammatory factors such as ROS, MMP-13, IL-6, and TNF-α. Meanwhile, SIRT4 promotes M2 polarization, increases the mRNA levels of Arg-1 and CD206 and enhances the expression of the IL-10 (133, 134). SIRT5 promotes the acetylation of p65 and activates the NF-κB signaling pathway to augment IL-1β production during inflammation (135, 136). SIRT7 activates the NF-κB signaling pathway, increases the expression of IL-1β, and promotes inflammatory responses (137). In contrast, SIRT6 upregulates the expression of anti-inflammatory cytokines IL-4 and IL-10, increases M2 polarization, and attenuates inflammatory responses (138).

The pre-activation state of macrophages also affects the function and expression of Sirtuins. NAD⁺ is an important cofactor regulating metabolic homeostasis and a rate-limiting substrate for sirtuin deacylases (139). Studies have shown that supplementation with NMN (a precursor of NAD⁺) increases NAD⁺ levels and activate SIRT3 (140). Under pro-inflammatory conditions, M1 macrophages produce large amounts of ROS through glycolysis, which may lead to the depletion of NAD⁺ and indirectly inhibit the enzymatic activity of SIRT1 and SIRT3 (59, 141, 142). In contrast, M2 macrophages rely on oxidative phosphorylation and may maintain higher NAD⁺ levels through fatty acid oxidation and OXPHOS, thereby activating SIRT3 and promoting anti-inflammatory and tissue repair functions (59, 141, 143, 144).

The NLRP3 inflammasome is a high-molecular-weight multiprotein complex composed of NLR family members that assembles in response to various stimuli in the cytoplasm (145); it plays a key role in host defense, inflammation, autoimmunity, and the development of metabolic diseases (146). Macrophages undergo profound metabolic reprogramming when they are sensing infections and sterile stimuli, and this metabolic shift supports and regulates the activation of the NLRP3 inflammasome (147).

The role of glycolysis in inflammasome activation is complex and involves enzymes involved in the glycolytic process and changes in glycolytic flux. The blockade of pyruvate kinase M2 (PKM2) limits the classical activation of NLRP3 in mouse BMDMs (148). In contrast, the inhibition of hexokinase 2 (HK2) by N-acetylglucosamine (NAG) leads to the detachment of HK2 from the mitochondrial outer membrane, thereby increasing inflammasome activation in mouse BMDMs (149). Effective glycolysis results in the conversion of NAD⁺ to NADH, the secretion of lactate, and the production of ATP. The inhibition of GAPDH and α-enolase, leading to the interruption of glycolytic flux, triggers the NLRP3 inflammasome in mouse BMDMs in a K⁺-independent manner (150).

Intermediates in the TCA cycle play a significant role in cellular signaling, including the regulation of NLRP3 inflammasome activation. The accumulation of itaconate is associated with the inhibition of the NLRP3 inflammasome. Irg1^−/− mouse BMDMs, which cannot synthesize itaconate, exhibit increased NLRP3 activation (114). Itaconate inhibits the activation of the NLRP3 inflammasome through various mechanisms, including posttranslational modifications of kelch-like ECH-associated protein 1 (KEAP1), NIMA-related kinase 7 (NEK7), and gasdermin-D (GSDMD) (151–155). Succinate plays a significant role in regulating NLRP3 inflammasome activation by succinylating the Cys192 site of GSDMD, inhibiting GSDMD oligomerization and pyroptosis (156).

Lipid metabolism is also crucial for NLRP3 inflammasome production. Saturated fatty acids (SFAs) can activate the NLRP3 inflammasome, whereas unsaturated fatty acids, such as oleic acid (OA), can counteract SFA-mediated NLRP3 activation or directly suppress NLRP3 activation (155, 157–159). Polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (DHA), can sense and inhibit LPS-preactivated human macrophage NLRP3 activation (151, 152).

In the cardiac tissue microenvironment, macrophages constitute the largest group of immune cells. Cardiac macrophages can be divided into two major categories: infiltrating macrophages and resident macrophages.

Infiltrating cardiac macrophages are mainly CCR2⁺ macrophages derived from recruited monocytes, which play a major role in the inflammatory response (179). After myocardial infarction, macrophages and other inflammatory cells infiltrate the infarct area, leading to the production of pro-inflammatory cytokines, exacerbating inflammation, and clearing necrotic tissue (180). In ischemic myocardial injury, CCR2⁺ macrophages infiltrated via MCP-1 dominate the inflammatory and fibrotic responses in the early stage of injury (181). Additionally, in dilated cardiomyopathy, NLRP3 inflammasomes synthesized by infiltrating macrophages can promote the cleavage of apoptosis-associated speck-like protein (ASC), caspase-1, IL-1β, IL-18, and GSDMD into their active forms, which will exacerbate inflammation, induce cardiomyocyte pyroptosis and promote myocardial fibrosis (182, 183).

Resident cardiac macrophages originate from different macrophage precursor cells and possess distinct functions and behaviors (184). Resident cardiac macrophages in the heart can be distinguished on the basis of their expression of CCR2; CCR2⁻ macrophages are derived from the primitive yolk sac and fetal monocyte precursors, whereas CCR2⁺ macrophages originate from hematopoietic progenitors in the blood (185, 186).

Under homeostatic conditions, resident cardiac macrophages are involved in a range of functions that are crucial for maintaining cardiac homeostasis. Studies have shown that CCR2⁻ macrophages, which originate from the yolk sac, are necessary for the proper remodeling of the coronary arterial plexus and the functional maturation of coronary vessels (187). These findings also suggest that macrophage-derived insulin-like growth factor 1 (IGF-1) is a potential mediator of coronary arteriogenesis (187). CCR2⁻ macrophage depletion in embryos leads to abnormalities in developmental processes and vascular maturation (187).

Resident cardiac macrophages mediate immune surveillance, which maintains the homeostasis of CCR2⁻ and CCR2⁺ macrophages that express MHC II and act as antigen-presenting cells; they function by processing and presenting antigens to circulating T cells (184). Moreover, CCR2⁻ resident cardiac macrophages expressing MERTK have a greater capacity for phagocytosing cardiac myocyte debris and contents than CCR2⁺ macrophages do. Several studies have described the efferocytosis of apoptotic cells by MERTK-expressing cardiac macrophages as an important contributing factor to cardiac homeostasis (188, 189). Additionally, MERTK-expressing resident cardiac macrophages in the hearts of young mice can protect the heart from infection by Mycobacterium avium, which has been shown to cause cardiac arrhythmias and promote bacterial dissemination to the cardiac tissues of older mice (190).

Importantly, studies have shown that resident cardiac macrophages promote mitochondrial homeostasis in cardiomyocytes (191). Mertk deletion in resident cardiac macrophages limits their phagocytic capacity and prevents them from taking up dysfunctional mitochondria (191). The disruption of mitochondrial clearance in macrophages impairs autophagy, leading to the accumulation of cellular debris and metabolic dysfunction in cardiomyocytes, which may result in impaired ventricular function (191).

With the development of technologies such as single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics, further classification of cardiac macrophage subsets has been achieved. Using scRNA-seq, trypanosome lytic factor (TLF⁺) macrophages have been identified (192–194). The replenishment of TLF⁺ macrophages is independent of circulating monocytes (192), and their transcriptomic features are mainly enriched in homeostatic functions, such as endocytosis, cellular transport, and angiogenesis (192, 193). The application of scRNA-seq in acute myocardial infarction research has further subdivided distinct subsets of cardiac macrophages. It was found that macrophages with high expression of interferon-stimulated genes (ISG⁺) and MHC-II⁺ macrophages are key pro-inflammatory subsets during the inflammatory phase, whereas macrophages with high expression of triggering receptor expressed on myeloid cells 2 (Trem2⁺) are the main anti-inflammatory subsets during the repair phase (194–196). A study using spatial transcriptomics analyzed different anatomical regions of the heart and identified a novel population of tissue-resident macrophages (LYVE1⁺ macrophages), which are present in the atrioventricular node and sinoatrial node (197). Another study utilizing spatial transcriptomics discovered a subset of monocyte-derived macrophages expressing basic helix-loop-helix family member e41 (Bhlhe41⁺) in the infarct area during the early stage of myocardial infarction (198). By analyzing spatial ligand-receptor interactions and combining experiments in animal models, the results showed that Bhlhe41⁺ macrophages can upregulate the secretion of progranulin (GRN). GRN antagonizes the effect of TNF-α on TNF receptor 1 (TNFR1), which will inhibit myofibroblast activation and limit the expansion of the infarct area (198). In the future, with the continuous advancement of technologies and in-depth research, the classification of cardiac macrophages will be further refined.

Cardiac macrophages participate in cross talk with fibroblasts, lymphocytes, endothelial cells, cardiomyocytes, and other cell types in the heart (199). Following myocardial infarction, pro-inflammatory M1-type macrophages release exosomes rich in miR-155, which suppress the expression of key genes such as Rac family small GTPase 1 (RAC1), p21-activated kinase 2 (PAK2), SIRT1, and AMP-activated protein kinase α2 (AMPKα2) in endothelial cells. This inhibition of gene expression could impair angiogenesis and exacerbates myocardial injury (200). During the healing phase of myocardial infarction, infiltrating cardiac macrophages can secrete Angiotensin II (Ang II), which activates the angiotensin II type 1 (AT1) receptor on fibroblasts, upregulates TGF-β1, induces the transformation of fibroblasts into myofibroblasts and increases collagen deposition (201). Meanwhile, infiltrating cardiac macrophages are capable of secreting exosomes enriched with miR-155; after being internalized by fibroblasts, these exosomes downregulate the expression of son of sevenless homolog 1 (SOS1) and inhibit fibroblast proliferation (202). Interestingly, the expression of angiopoietin 2 (Angpt2) in endothelial cells is increased, and Angpt2 can promote the polarization of macrophages toward a pro-inflammatory phenotype via the α5β1/extracellular ERK pathway (203). Similarly, after myocardial infarction, neutrophil gelatinase-associated lipocalin (NGAL) in the secretome of neutrophils affects the proliferation of cardiac macrophages by modulating the expression of the macrophage receptor MertK on the cardiac macrophage membrane (204). In the absence of NGAL, the expression of MertK on the cardiac macrophage membrane is reduced, which impairs the phagocytic capacity of macrophages (204). Th1 cells promote the polarization of pro-inflammatory macrophages, whereas Th2 cells and Treg cells (which secrete IL-10 and TGF-β) facilitate the acquisition of an anti-inflammatory macrophage phenotype. These regulatory effects ultimately influence myocardial healing and scar formation (205). A pioneering study reported that resident cardiac macrophages promote electrical conduction in the heart by intermingling with distal atrioventricular nodal conduction cells through macrophages expressing connexin 43 (206). Both mouse and human hearts are rich in CCR2⁻ and CCR2⁺ macrophages in the atrioventricular node (206). Resident cardiac macrophages in the atrioventricular node maintain direct contact with cardiomyocytes through gap junctions. The removal of resident cardiac macrophages or conditional knockout of the Gja1 gene, which encodes connexin 43, leads to impaired atrioventricular conduction, ultimately resulting in atrioventricular block, thereby confirming that resident cardiac macrophages are necessary for cardiac electrical conduction. Furthermore, compelling studies have indicated that sudden cardiac death due to arrhythmias caused by myocardial infarction is a result of an imbalance in the cardiac leukocyte population (207, 208). More specifically, researchers have described an “electrical storm,” during which rapidly infiltrating neutrophils contribute to ventricular tachycardia (207, 208). The depletion of CCR2⁻ resident cardiac macrophages or complete depletion of macrophages leads to an increased incidence of arrhythmias, demonstrating that macrophages have a protective effect on electrical conduction after myocardial infarction.

Atherosclerosis (AS) is a process characterized by the formation of fibrofatty lesions in the intima of arteries, a term derived from Greek, meaning “gruel-like,” which vividly describes the lipid core of typical atherosclerotic plaques (209, 210). Over time, atherosclerotic plaques become more fibrotic and accumulate calcium (209). Plaques can trigger thrombosis and cause tissue ischemia by obstructing blood flow through rupture, superficial erosion, or protrusion into the arterial lumen (211). Inflammation plays a crucial role in AS development. Atherosclerotic plaques harbor a variety of inflammatory cells, such as monocytes/macrophages and T cells. These cells are recruited to sites of arterial wall injury, where they release a range of inflammatory factors, including cytokines (IL-1, IL-6, TNF-α, etc.), which contribute to the inflammatory response (212, 213). After engulfing oxidized low-density lipoprotein (oxLDL), monocytes/macrophages transform into foam cells, and the accumulation of foam cells is one of the key features of atherosclerotic plaque formation (214).

Macrophages are involved in the occurrence, development, and regression of AS. The recruitment and polarization of macrophages and the formation of foam cells can affect the fate of plaques (66). When the endothelium is exposed to atherogenic risk factors, endothelial cells are disturbed. These risk factors include oxidized and other modified LDL particles, pro-inflammatory cytokines, local disturbances in the hemodynamic environment, and cardiovascular-related risk factors (215, 216). Activated endothelial cells express adhesion molecules and chemokines, which promote the rolling, adhesion of circulating monocytes to the endothelium, and the migration of bound monocytes into the arterial wall (217).

Histological analyses of human plaques have revealed varying numbers and degrees of macrophages. M1 macrophages are located primarily in lipid-rich areas away from M2 macrophages; these macrophages change their phenotypic expression over time, depending on their location and microenvironment, all of which regulate plaque progression and composition (66). Macrophages take up oxidized lipid particles and transform into cholesterol-filled foam cells, which is an early event in plaque formation. The formation of foam cells is associated with multiple transcription factors that play key roles in macrophage polarization and the development of atherosclerosis (218). The dynamic equilibrium of macrophages within atherosclerotic plaques is a complex process involving multiple aspects, including recruitment, retention, polarization, egression, and death. The interplay of these processes determines the inflammatory status and stability of the plaque (219). In the early stages of atherosclerosis, the dominant M2 macrophages help maintain the stability of the arterial wall (220). However, as the disease progresses, the proportion of M1 macrophages gradually increases, while the proportion of M2 macrophages relatively decreases. This imbalance exacerbates the inflammatory response and promotes the development of atherosclerosis (221).

Myocardial infarction (MI) is a clinical condition characterized by cardiomyocyte death and tissue injury resulting from myocardial oxygen deprivation. The loss of cardiomyocytes is accompanied by alterations in cellular composition, which in turn elicits an inflammatory response and triggers remodeling of the ischemic myocardium (222). Various cells, including cardiomyocytes, endothelial cells, neutrophils, monocytes/macrophages, lymphocytes, and fibroblasts, are involved in the inflammatory response. These cells promote the infiltration of inflammatory cells and the clearance of tissue damage by releasing cytokines, chemokines, and cell adhesion molecules (180). MI is one of the leading cardiovascular diseases worldwide, and its high incidence and mortality rates pose a significant burden on society and healthcare systems (223). Immune inflammation plays a crucial role in MI and subsequent ventricular remodeling, significantly impacting the extent of tissue damage, cardiac function, and disease prognosis (224). As essential innate immune cells, macrophages play a vital role in immune responses, pathogen clearance, and tissue repair (225). After MI, there are significant changes in the subpopulation distribution, metabolic characteristics, and functional phenotypes of cardiac macrophages, which promote inflammation, dead cell debris clearance, inflammation/repair transition, tissue repair promotion, and other functions at different stages (184, 226).

The insufficient cardiac blood perfusion after MI leads to a lack of oxygen and nutrients, cell damage, and the release of DAMPs. These environmental changes trigger adaptive alterations in macrophage metabolic pathways, significantly affecting their movement, phagocytic functions, and cellular phenotypes, thereby influencing the role of macrophages in disease occurrence and development (111, 224). Transcriptome profiling has revealed differential gene enrichment in glycolytic pathways in macrophages on the first day post-MI; metabolic flux analysis has revealed that macrophage glycolysis increases on the Day 1 and Day 3 post-MI. Enhanced glycolysis in macrophages early after MI is conducive to their adaptation to hypoxic environments and activation (227). Mechanistically, macrophages post-MI recognize DAMPs released from necrotic cells through Toll-like receptors (TLRs), activating downstream signaling pathways such as the mTOR pathway and entering an activated state with increased energy demands (224, 226). Hypoxia-induced factor (HIF)-1α, a downstream molecule of the TLR–mTOR axis, increases in expression post-MI and enhances glycolysis by upregulating the expression of key enzymes in the glycolytic pathway, such as hexokinase 1, lactate dehydrogenase, and glucose transporter 1 (228). In a mouse MI model, the double knockout of HIF-1α and HIF-2α reduces macrophage glycolytic levels, leading to increased macrophage necrosis, impaired tissue fibrosis, and increased cardiac rupture in mice, suggesting that increased macrophage glycolysis post-MI is beneficial for their survival in hypoxic environments (229). Additionally, the enhancement of glycolysis in macrophages post-MI provides energy for cell movement, phagocytosis, and the secretion of inflammatory factors while reducing oxygen consumption, meeting their increased energy demands upon activation (119, 184, 226).

To date, there is a lack of research evidence on lipid synthesis metabolism in macrophages post-MI. Some studies suggest that macrophages enhance FAO when phagocytosing necrotic cells post-MI, activating NAD⁺-dependent signal transduction and promoting the SIRT1–Pbx1–IL-10 metabolic signaling pathway, which promotes macrophage polarization toward the M2 type and improves cardiac damage repair post-MI (230). The changes in amino acid metabolism in macrophages post-MI have also been less studied. Glutamine metabolism in macrophages increases post-MI in mice, and exogenous glutamine supplementation can improve left ventricular function on the first, third, and seventh days post-MI (231). Recent studies have found that during the subacute phase of myocardial infarction, TREM2⁺ macrophages are recruited to the infarcted myocardial tissue and show upregulation of anti-inflammatory genes (232). These cells, derived from myeloid cells, play an important role in myocardial infarction repair (233). After efferocytosis, TREM2⁺ macrophages inhibit the mitochondrial NAD⁺ transporter SLC25A53 via the SYK-SMAD4 signaling pathway. This affects mitochondrial NAD⁺ transport, interrupts the TCA cycle, and increases itaconate production. Itaconate, an anti-inflammatory metabolite, helps regulate macrophage function and cardiac repair after myocardial infarction (233).

Myocarditis is an inflammatory heart disease that may be triggered by infections, exposure to toxic substances, and activation of the immune system. It is classified as a secondary cardiomyopathy in the 1996 World Health Organization classification (234). The most thoroughly studied to date is enterovirus infection, particularly myocarditis caused by Coxsackie virus B3 (CVB3) infection (235). The mechanisms by which this virus causes myocardial injury include both direct viral damage and immune-mediated damage. The innate immune response of the host is excessively activated (236, 237), leading to the release of a large number of inflammatory factors and the formation of a cytokine storm, which is the main mechanism causing severe myocardial injury and pump failure (238).

Research on the role of macrophages in myocarditis has focused primarily on the M1 and M2 polarization phenotypes, with a general consensus that M1 macrophages exacerbate myocarditis, whereas M2 macrophages alleviate myocardial inflammation. In viral myocarditis caused by CVB3, macrophages are enriched in cardiac tissue as early as the third day post infection (239), and they secrete high levels of IL-1β, which triggers the upregulation of NLRP3 in macrophages, potentially polarizing them to the M1 phenotype (240, 241). M1 macrophages are characterized by enhanced glycolysis and disrupted TCA cycle, leading to the accumulation of HIF-1α and the expression of pro-inflammatory factors (iNOS, IL-1β, IL-6) (242). This further exacerbates inflammation, creating a vicious cycle. The adoptive transfer of M1 macrophages significantly promotes myocarditis in mice. Transferring M2 macrophages into susceptible male mice significantly reduces myocardial inflammation by modulating local cytokines (243). Similarly, in myocarditis induced by CVB3, IL-13 deficiency increases the severity of CVB3-induced myocarditis by reducing the number of M2 macrophages but does not affect viral replication in the heart postinfection. The reduction in M2 macrophages leads to a significant increase in the levels of IL-1, IL-18, IFN-α, TGF-β, IL-4, and histamine, as well as an increase in CD4⁺ T cells and autoreactive antibodies (244). In the experimental autoimmune myocarditis (EAM) model, macrophages are one of the major cellular components of cardiac inflammation. Studies have shown that they are not only key players in the inflammatory response but also regulate disease progression and tissue repair through interactions with different immune cells (245). Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates macrophages to secrete IL-6, which in turn promotes the development of Th17 cells and enhances autoimmune reactions. The IL-17 secreted by Th17 cells can further activate macrophages, forming a positive feedback loop (246). Prominin-1⁺/CD133⁺ cells (a type of hematopoietic cell with stem cell characteristics) can differentiate into macrophages with immune regulatory functions in EAM. These macrophages can secrete anti-inflammatory cytokines (such as IL-10) to suppress inflammatory responses, alleviating the severity of myocarditis (247). IL-13 alleviates the severity of myocarditis by regulating the polarization and function of monocytes/macrophages. Its absence may lead to enhanced T cell activation and altered macrophage activation states, resulting in exacerbated myocarditis, cardiac fibrosis, and heart failure (244). During the chronic phase of myocarditis, Ly6C^high monocytes infiltrated the heart transition into Ly6C^low macrophages, while Ly6C^low monocytes continue to infiltrate the heart and differentiate into macrophages (248). These macrophages predominantly exhibit an M2 phenotype and secrete a variety of cytokines that mediate tissue repair: arginase 1, TGF-β, and IL-10 induce myofibroblasts to produce collagen, VEGF promotes angiogenesis, and MMPs along with tissue inhibitors of metalloproteinases (TIMPs) regulate the extracellular matrix network. In contrast, TNF-α and IL-1 secreted by M1 macrophages stimulate fibroblasts to secrete excessive extracellular matrix, leading to matrix deposition and maladaptive fibrosis (249).

Inflammation in heart allograft rejection is one of the important factors leading to transplant failure, including hyperacute rejection, acute rejection, and chronic rejection. Hyperacute rejection is an immune response that occurs rapidly, usually within minutes to hours after transplantation. The inflammatory manifestations include vascular congestion, thrombosis, hyaline microthrombi, and necrotizing vasculitis of small to medium-sized vessels (250). Acute rejection includes acute cellular rejection (ACR) and antibody-mediated rejection (AMR). ACR is mainly mediated by T cells and is the most common type of rejection after cardiac transplantation, usually occurring within 3 to 6 months after transplantation. The inflammatory manifestations include T cell infiltration and cytokine secretion like IL-2, TNF-α, leading to myocardial injury and necrosis (251). AMR is caused by B cells producing antibodies against donor antigens, leading to graft injury through complement activation and inflammatory cell infiltration (252). Chronic rejection, also known as cardiac allograft vasculopathy (CAV), is one of the long-term complications after cardiac transplantation. The inflammatory manifestations include intimal thickening of the coronary arteries, leading to luminal stenosis (253).

The accumulation of macrophages and rejection macrophages has long been considered a characteristic of allograft rejection, with the total number of graft-infiltrating macrophages being associated with poorer clinical outcomes (28, 254). The heart contains both CCR2⁺ and CCR2⁻ macrophages, which exhibit different phenotypes under homeostatic conditions (17). After transplantation, the macrophage population in the heart includes donor-derived CCR2⁺ and CCR2⁻ macrophages, as well as recipient-derived neutrophils, monocytes, monocyte-derived macrophages, and monocyte-derived dendritic cells (255–257). These cells play different roles in rejection and tolerance. CCR2⁺ macrophages are enriched in proinflammatory genes, and their activation represents a mechanism that drives inflammation; CCR2⁻ macrophages promote coronary arteriogenesis and cardiomyocyte proliferation through the secretion of IL-10 and TGF-β and possess potential anti-inflammatory effects (17). Studies have found that MEK1/2 promotes the pro-inflammatory phenotype and glycolytic capacity of alloimmune infiltrating macrophages (AIMs) by regulating PKM2 expression and nuclear translocation, playing a key role in cardiac transplant rejection (258). Further research is needed to elucidate the roles of macrophage metabolism and polarization in cardiac transplant rejection, including their mechanisms in various rejection types and potential therapeutic targets.

Valvular heart disease can be categorized into primary and secondary types. Primary (or degenerative) disease is caused by intrinsic dysfunction of the valve itself, whereas secondary (or functional) disease results from underlying myocardial pathology (259). Inflammatory responses in valvular heart disease involve the activation of endothelial cells and immune cells, which secrete inflammatory cytokines such as TGF-β1, TNF-α, IL-1β, and IL-2, and they promote disease progression (260).

Valvular heart disease is a leading cause of disability and diminished quality of life and is a major contributor to cardiovascular morbidity and mortality worldwide (261). In recent years, an increasing number of studies have highlighted the significant role of macrophages in the development of valvular heart disease (262). In myxomatous valve disease (MVD), there is an increase in the number of CCR2⁺ monocytes and CD206⁺ macrophages, and the accumulation of these cells in immune-active extracellular matrix remodeling areas of the valve leaflets may be associated with disease progression (263). In calcific aortic valve disease (CAVD), macrophages increase infiltration and maturation in response to inflammatory factors secreted by aortic valve cells, thereby promoting osteogenic calcification, affecting the splicing of STAT3 and reducing the expression of the STAT3β isoform, which may promote disease progression (264). Macrophages, particularly the M2 subtype, play a key role in calcific aortic stenosis, and their expression of the pattern recognition receptor Toll-like receptor 7 (TLR7) is associated with inflammation and calcification processes in the aortic valve (265). The activation of TLR7 leads to increased secretion of the immunomodulatory cytokine IL-10, which may help mitigate inflammatory responses and promote valve tissue repair (265). Few studies have explored the role of macrophage metabolism and polarization in valvular heart disease. More research should be devoted to understanding their specific mechanisms in disease progression and repair.

Heart failure (HF) is a multifactorial cardiovascular disease characterized by impaired cardiac pumping function, leading to inadequate organ perfusion and oxygenation (266). Classified by left ventricular ejection fraction (LVEF), HF is typically categorized into heart failure with reduced ejection fraction (HFrEF), heart failure with mildly reduced ejection fraction (HFmrEF), and heart failure with preserved ejection fraction (HFpEF) (266). Endothelial inflammation, activation of the innate immune system, and humoral immunity can all affect the structure and function of the heart, leading to heart failure (267). Heart failure itself can also cause sterile inflammation, with cardiomyocytes and cardiac fibroblasts releasing pro-inflammatory cytokines (such as TNF-α, IL-6, IL-1β) when subjected to mechanical stretching and increased wall tension, activating the NLRP3 inflammasome and further exacerbating inflammation (268). Acute myocardial infarction (AMI) is a major cause of heart failure (269). When AMI occurs, Ly6C^high monocytes are the first monocytic population to arrive. They differentiate into M1 macrophages, produce proteases, and secrete MMPs that degrade dying cardiomyocytes and the extracellular matrix (ECM) (270). Hypoxia-inducible factors (HIFs) rapidly accumulate in the nuclei of macrophages in response to the hypoxic microenvironment (271). HIFs promote the transcription of the M1 macrophage gene profile and shift glycolysis to become the primary mode of metabolic energy production in M1 macrophages by driving the expression of the glycolytic gene Slc2al (272).

Clinically, in HF patients undergoing left ventricular assist device implantation, the proliferation of CCR2⁺ macrophages is correlated with the deterioration of left ventricular function and chamber dilation (255). Moreover, these CCR2⁺ macrophages enriched in the hearts of these patients also produce large amounts of IL-1β upon exposure to necrotic cardiomyocytes. IL-1β is known to predict adverse outcomes in HFrEF patients (273). In myocardial biopsies from HFpEF patients, the number of cardiac macrophages is doubled (274), and there is an increase in the gene expression of profibrotic TGF-β (275). These events seem to contribute to the activation of fibroblasts and excessive deposition of collagen (274, 275). Cardiac macrophages also secrete galectin-3, which promotes myocardial fibrosis by activating myofibroblasts (276), as well as phagocytosis-induced TGF-β expression (277). In HFpEF patients, plasma levels of galectin-3 are significantly increased, and elevated levels are associated with a worse prognosis (278).

Arrhythmias refer to abnormalities or perturbations in the normal activation or beating of the myocardium. The normal cardiac rhythm is initiated by the sinoatrial (SA) node and conducted through the atrioventricular (AV) node and the His-Purkinje system, resulting in systematic ventricular depolarization. There are numerous types of cardiac arrhythmias. Sinus rhythm, the normal cardiac rhythm, can be disrupted by sinoatrial node dysfunction or inappropriate sinus tachycardia. Additionally, premature atrial contractions and premature ventricular contractions may occur. The severity of arrhythmias is associated with the presence or absence of structural heart disease. Atrial fibrillation (AF) is generally considered benign; however, structural heart diseases such as coronary artery disease or left ventricular dysfunction superimposed with AF may lead to heart failure or sudden cardiac death (279). Inflammation induces atrial arrhythmias by promoting atrial fibrosis, abnormal regulation of gap junctions, and intracellular calcium regulation, causing atrial electrical and structural remodeling (280). Inflammatory markers such as CRP, hs-CRP, and IL-6 are associated with the incidence and duration of atrial fibrillation (280). Following myocardial infarction, macrophages shift toward the M1 phenotype, which impacts the electrical properties of cardiomyocytes via gap junctions and KCa3.1 channel. This leads to variability in cardiomyocyte action potential duration (APD) and contributes to the development of arrhythmias (281).

In both human and murine atrioventricular nodes, CCR2⁻ and CCR2⁺ macrophages are present (282). Cardiac macrophages facilitate signal transmission between cardiomyocytes through connexin 43, thereby maintaining cardiac impulse conduction. Macrophage-produced dual-regulatory proteins are key mediators controlling the phosphorylation and translocation of connexin 43 (206, 283). In vivo, the depletion of cardiac resident macrophages or macrophage gap junction protein 43 leads to impaired cardiac conduction (282). Macrophages can promote sympathoexcitation, and proinflammatory factors produced by macrophages, such as IL-1β, IL-6, and TNF-α, can activate the sympathetic nervous system through the circulation or afferent fibers, forming a substrate for proarrhythmia and directly affecting cardiac electrophysiology (284). Recent studies have shown that in atrial fibrillation, the expansion of a subset of macrophages, particularly those positive for secreted phosphoprotein 1 (SPP1), plays a key role in the development of arrhythmias; they promote inflammation and fibrosis through interactions with local cardiac immune and stromal cells, providing a conducive environment for the occurrence and maintenance of atrial fibrillation (285). Currently, there are limited studies on the role of macrophage polarization and metabolic changes in arrhythmias, and more researches are needed to fill this gap.

Aortic aneurysm (AA) is a chronic aortic disease characterized by permanent, localized dilatation of the aorta resulting from pathological remodeling of the aortic wall. It can further progress to fatal aortic rupture, which is associated with a high mortality rate (286). Aortic rupture is not only associated with the continuous enlargement of the aneurysm diameter; multiple pathological processes also contribute to this progression, including ECM degradation, inflammation, phenotypic transformation of vascular smooth muscle cells (SMCs), oxidative stress, and neovascularization (287). Macrophages play a crucial role in all stages of aortic aneurysm development. M1-type macrophages promote the progression of AA by secreting inflammatory factors and MMPs, which facilitate extracellular matrix destruction and apoptosis of vascular smooth muscle cells (VSMCs). In contrast, M2-type macrophages are mainly involved in vascular repair by inhibiting inflammation (288, 289).

When arteries are damaged, monocytes are recruited to the injury site under the guidance of chemokines such as CCR2 and CCR1, and further differentiate into macrophages (290). Inflammation is one of the core characteristics of aortic aneurysms, and macrophages play a key regulatory role in this process (197). During the clearance of early cellular debris, M1 macrophages generate large amounts of ROS. These ROS act synergistically with ROS derived from endothelial cells, vascular smooth muscle cells, and other immune cells in the aortic wall to continuously activate macrophages, forming a vicious cycle that amplifies the inflammatory response (197, 291). Additionally, M1-type macrophages can secrete pro-inflammatory cytokines such as TNF-α and IL-1β, which further drive the inflammatory process (289, 292). In contrast to M1 macrophages, M2 macrophages secrete anti-inflammatory factors such as IL-10 and TGF-β to inhibit the production of inflammatory mediators and MMPs, and they can also clear free hemoglobin and regulate oxidative stress, which will promote vascular remodeling and repair (288, 293). This process may involve the upregulation of the transcription factor Krüppel-like factor 6 (KLF6) or the downregulation of PPARδ activity (294, 295).

The immune system is essential for defending the body against external pathogens and maintaining homeostasis. However, as people age, the functionality of the immune system gradually declines, a process known as “immunosenescence.” This phenomenon describes the weakening of the immune system associated with aging, characterized by alterations in immune cell populations and functional impairments of both innate and adaptive immunity. As a result, immunosenescence leads to increased susceptibility to infections and various chronic inflammatory diseases (299). Moreover, the aging of the immune system is a cause of immune dysfunction, which can eliminate senescent cells and lead to acquired tissue damage (300). Inflammaging is a chronic, sterile, low-grade inflammatory state associated with aging and is an important hallmark of immunosenescence. This condition is characterized by persistent immune activation and elevated levels of pro-inflammatory cytokines in the circulation, such as TNF-α, IL-6, and IL-1β (301).

The role of immunosenescence in inflammation-related heart diseases is increasingly being investigated. During the process of inflammaging, macrophages accumulate in the arterial wall, where they take up lipids from the blood, particularly LDL, leading to the formation of foam cells. As foam cells accumulate within the arterial wall, they contribute to the formation of atherosclerotic plaques, resulting in vessel stenosis or occlusion (219). With advancing age, the production of NAD⁺ and the levels of NAD⁺-dependent enzymes, such as the SIRT family, decrease in macrophages. This reduction affects the regulation of NF-κB activity, leading to heightened inflammatory responses (302). In aged individuals, the prolonged course of wound repair is associated with prolonged inflammation, delayed neovascularization, and delayed restoration of the extracellular matrix (303). Studies have shown that in aged mice following myocardial infarction, there is impaired inflammation characterized by decreased and delayed neutrophil and macrophage infiltration, reduced cytokine and chemokine expression, and impaired phagocytosis of dead cardiomyocytes. These factors may lead to maladaptive vascular remodeling and tissue repair in the healing heart, accelerating the transition to heart failure (304).

Previous researchers believed that innate immune cells, such as macrophages, could only non-specifically eliminate pathogens through biological processes like phagocytosis. However, an increasing number of studies have shown that monocytes/macrophages may also develop memory capabilities similar to those of the adaptive immune system after exposure to pathogens (305). Myeloid cells of the innate immune system become more sensitive after activation with the same or different stimuli, resulting in a persistent inflammatory monocyte/macrophage phenotype. This phenomenon is known as “trained immunity” or “innate immune memory” (306). This persistent overactivation of the innate immune system may promote the progression of inflammatory cardiovascular diseases. Risk factors for cardiovascular diseases, such as diet, smoking, hypercholesterolemia, and diabetes, are often associated with low-grade inflammation, which can induce trained immunity and subsequently affect bone marrow hematopoietic progenitor cells through epigenetic modifications, leading to chronic metabolic disorders and vascular inflammation (307). Bekkering et al. (308) proposed that trained innate immunity is associated with the progression of atherosclerosis. Wang et al. (309) also found that trained monocytes/macrophages undergo metabolic and epigenetic changes that keep these cells in a state of chronic overactivation, thereby exacerbating atherosclerosis. Myocardial infarction reprograms bone marrow monocytes through epigenetic modifications, and transplantation of bone marrow from infarcted mice to other mice results in aggravated atherosclerosis and increased infiltration of myeloid cells into plaques (310).