Neutrophils are short-lived cells that are delivered to tissues in periodic waves through circadian release from the bone marrow. In mice, CXCR4-CXCL12 signaling mediates bone marrow retention, whereas CXCR2-CXCL1/2 signaling promotes rhythmic egress (56) and resting-phase (ZT2) infiltration into the liver, where neutrophil elastase enhances hepatocyte Bmal1 and Clock expression and lipogenesis. In humans, only the correlation of circadian co-oscillation with ELANE and BMAL1 has been observed rather than causality (57). Consequently, their spatial distribution within the liver is unlikely to reflect stable residence and is plausibly determined by where incoming neutrophils are preferentially captured, retained, or cleared (58, 59).

The hepatic vasculature further reinforces their spatial patterning. Unlike in most organs, neutrophils in the liver bypass selectin-mediated rolling and instead undergo direct adhesion or mechanical trapping within low-shear sinusoids (60). This unique entry mechanism is inherently shaped by a sinusoidal structure, which features a discontinuous endothelial lining that facilitates physiological neutrophil capture. As a result, the hepatic zonated architecture not only influences whether neutrophils enter but also where they localize and how long they persist.

In the steady-state liver, neutrophils are relatively enriched in periportal regions, where they coexist with pathogen-sensing Kupffer cells (2, 36, 37). During liver injury, neutrophil spatial dynamics are reshaped in an insult-dependent manner (58). Sterile toxic injury and partial hepatectomy preferentially drive pericentral accumulation, whereas microbial or bile acid-related signals promote periportal activation (31, 61). Thus, neutrophil zonation in the liver reflects a dynamic balance between wave-like systemic supply and local hepatic cues that regulate recruitment, retention, and egress across physiological and pathological states.

Neutrophil infiltration becomes particularly prominent in liver diseases where injury is spatially restricted. Toxic and metabolic injuries, such as APAP hepatotoxicity (40, 41), carbon tetrachloride (CCl₄) exposure (41), ischemia-reperfusion (I/R) injury (40), and metabolic dysfunction-associated steatotic liver disease (MASLD/MASH) (39), preferentially damage the pericentral region, creating hypoxic, reactive oxygen species (ROS)-rich, DAMP-dense microenvironments that strongly attract neutrophils. Live imaging using LysM-eGFP mice has demonstrated that neutrophils crawl along sinusoidal endothelium using β2-integrins and follow hierarchical chemotactic cues, first sensing CXCR2 ligands near necrosis and then migrating toward mitochondrial formyl peptides released by dying hepatocytes (3, 62).

As neutrophils reach necrotic pericentral foci, their directed migration transitions to nondirectional patrolling, enabling them to scan the injury bed even when chemokine gradients diminish (63). This selective neutrophil enrichment amplifies monocyte recruitment signals, setting the stage for the accumulation of inflammatory and reparative macrophages that orchestrate tissue remodeling (64, 65).

Neutrophil adhesion mechanisms also exhibit zonal and context-dependent variability. During systemic inflammation, CD44-hyaluronan interactions dominate neutrophil arrest in hepatic sinusoids (66), whereas local chemoattractants shift reliance toward ICAM-1/integrin-mediated adhesion (63, 67). These dynamic adaptations were validated through endotoxemia models (66) highlight that neutrophil accumulation in specific zones is not passive trapping but an actively regulated, stimulus-dependent process.

Zonated neutrophil accumulation has profound consequences for the progression of liver injury. In pericentral necrotic regions, neutrophils amplify tissue damage by releasing ROS, proteases, and pro-inflammatory cytokines, thereby exacerbating hepatocellular damage (58, 68, 69). Their rapid recruitment functions as a spatial checkpoint for subsequent immune escalation, as shown in Con-A-induced hepatitis (70), where early neutrophil activation through L-selectin shedding and ROS production facilitates CD4⁺ T-cell infiltration (60). These observations position neutrophils as zone-specific “gatekeepers” that translate microanatomical context into coordinated inflammatory and adaptive immune responses.

In vivo imaging has further revealed that neutrophils produce neutrophil extracellular traps (NETs) in response to endotoxin or bacterial stimuli (71, 72). NETs, DNA-protein lattices with microbicidal properties (59), also exhibit potent pro-inflammatory activity in the liver (73). During I/R injury, DAMPs, such as HMGB1 and IL-33 originating from stressed hepatocytes and LSECs, drive robust neutrophil infiltration and NET formation (40, 49, 68, 74). Superoxide-mediated activation of TLR4-NOX pathways provides an additional trigger (75). Interventions that degrade NETs by Dnase or inhibit their formation by PAD4 inhibitors markedly attenuate liver inflammation (72, 74), underscoring NETosis as a therapeutic target in I/R injury.

Neutrophils also contribute to tissue remodeling and fibrogenesis through zone-dependent mechanisms. In pericentral injury models, ROS and DAMP accumulation strongly induce NETosis. NETs sustain inflammatory signaling and augment monocyte recruitment, and the associated release of histones, proteases, and chemokines activate hepatic stellate cells (HSCs). This environment favors the transition of pericentral HSCs into collagen-producing myofibroblasts, key drivers of progressive fibrosis. Blocking NET formation reduces NASH-HCC progression and mitigates inflammation, implying the pathological relevance of neutrophil-centered zonal networks (73).

Despite their tissue-damaging potential, neutrophils also contribute to repair. Their removal of cellular debris, containment of microbial translocation, and facilitation of macrophage differentiation collectively promote resolution (61). However, the outcome of neutrophil action between injury amplification and repair initiation is largely determined by the zone in which they accumulate, as each lobular region imposes distinct metabolic, stromal, and immunological cues that differentially shape neutrophil function. Pericentral niches enriched in hypoxia, ROS, and hepatocyte-derived DAMPs drive cytotoxic programs and NETosis, whereas periportal environments dominated by microbial signals and tolerogenic cytokines favor debris clearance by neutrophils and restrain excessive neutrophil activation. Thus, the functional imprint of neutrophils is inseparable from the hepatic spatial organization, highlighting zonation as a critical determinant of inflammatory dynamics, fibrogenic progression, and regenerative trajectories.

KCs are the dominant tissue-resident macrophages of the liver and are positioned primarily within periportal to midzonal sinusoids (26, 39). Their asymmetric distribution is not developmentally pre-determined but arises from sustained exposure to gut-derived microbial products via MyD88-dependent signaling in LSECs (3), along with chemokine gradients that retain KCs in zone 1 (39). Periportal MARCO⁺ F4/80⁺ CLECF4⁺ KCs specialize in clearing bacteria (3, 76) entering through the portal vein and maintaining immune tolerance by producing IL-10 and scavenging microbial metabolites (3). Under pathological conditions, however, KC identity and localization are altered. During steatosis, VSIG4⁺ FOLR2⁺ CD163⁺ CD169⁺ KCs are enriched in zone 2 (39), whereas acute liver injury is characterized by the emergence of MARCO^- F4/80⁺ KCs in zone 3 (3). In chronic injury, KCs enriched in zone 3 progressively acquire a LAM-like phenotype, characterized by expression of TREM2⁺ GPNMB⁺ TIM4⁺ CLEC4F⁺ F4/80^int CD36^hi (41). Although early single-cell studies debated KC heterogeneity (8, 26), recent spatial profiling has clarified that KCs possess zonally distinct identities shaped by their microanatomical context (39, 77).

In homeostasis, KCs remain largely immobile and maintain liver immune equilibrium by removing pathogens, apoptotic cells, and toxins, while suppressing unnecessary inflammation (39, 78). However, their distribution is prone to modulation by physiological stress and disease. Age-related functional decline (79), chronic inflammation, and metabolic injury result in marked KC depletion, particularly in periportal niches, which subsequently replenished by circulating monocytes (80). This process is dynamically regulated rather than stochastic, as monocytes trafficking and tissue infiltration follow circadian rhythms coordinated by cell-intrinsic clocks and hepatic cues (81, 82). The zonated hepatic microenvironment determines whether these incoming monocytes acquire tolerogenic KC-like identity or retain inflammatory programs, particularly in the milieu dominated by pathogen-associated molecular pattern (PAMP) or DAMP signals, pro-inflammatory cytokines, and metabolic stress. These dynamics underscore macrophage identity as a spatially governed state.

Acute and chronic liver injury deplete resident KCs, allowing monocytes to migrate toward the vacant KC niches, where they differentiate into monocyte-derived macrophages (MoMFs) (46). In fibrosis-prone regions, particularly pericentral zone 3, these MoMFs accumulate in proximity to HSCs (42), where they contribute to the early phases of fibrogenesis and inflammation. Spatial omics data support this pattern, revealing macrophage-HSC niches forming specifically around injury-associated fibrotic bands (42).

Metabolic and immune perturbations further diversify the reprogramming trajectories of MoMFs (35, 44). In MASLD/MASH (3, 41, 43, 45, 46) and cholestatic disorders [e.g. primary biliary cirrhosis (83, 84) and primary sclerosing cholangitis (83)], MoMFs accumulate in distinct zones depending on the dominant insult. Some MoMFs localize periportally, contributing to ductular reaction (83), while others cluster near steatotic or pericentral regions in response to lipid overload or hepatocyte stress (39). These findings highlight that macrophage zonation is not static but reflects the dynamic mapping of macrophage subsets to metabolic, immunological, and stromal cues present in specific hepatic regions.

Furthermore, depending on gradients of oxygen, metabolites, cytokines, and DAMPs, MoMFs may adopt inflammatory phenotypes, lipid-associated macrophage (LAM) states, or transition toward KC-like identity (41, 43–46). Cholangiocyte-derived signals can recruit MoMFs to periportal areas during ductular reaction after 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) injury (85, 86), whereas steatotic hepatocytes drive MoMF accumulation in pericentral or panzonal patterns in MASLD/MASH (41, 43, 45, 46). Thus, macrophage plasticity reflects not only their ontogeny but also the zonated biochemical landscapes into which they are recruited.

As fibrosis progresses, MoMFs diversify into specialized subsets, including LAMs and scar-associated macrophages (SAMs), characterized by TREM2, CD9, and osteopontin (28, 41, 43, 46, 47). These populations preferentially localize to collagen-rich, inflamed, or ECM-remodeling regions (28). Spatial transcriptomics further demonstrated that TREM2⁺ macrophages form structured fibrotic niches (8, 41, 46, 84, 87), and circulating soluble TREM2 correlates with MASH severity (87), highlighting their combined fibrogenic and metabolic roles.

In advanced fibrosis and cirrhosis, resident TIMD4⁺/MARCO⁺ KCs progressively diminish (32), whereas SAMs expressing TREM2 and CE9 accumulate along pericentral and bridging fibrotic septa (28). These SAMs directly interact with HSCs through TGF-β, PDGF, and CCL/MMP signaling, promoting myofibroblast activation and extracellular matrix deposition (88). Their spatial co-localization with HSCs within pericentral fibrotic niches provides a mechanistic link between zonated macrophage recruitment, HSC pathogenic transformation, and progressive collagen production.

Macrophage plasticity also influences regeneration. Following KC depletion, MoMFs repopulate hepatocellular interfaces and support repair through phagocytosis (45), efferocytosis (41), and secretion of pro-regenerative mediators (89). In fibrotic liver, MoMFs can fuse to form multinucleated macrophage syncytia, a process that restores KC-like functions by enhancing phagocytic capacity. This fusion-mediated reprogramming is critical for regeneration, as failure to form syncytia leads to impaired debris clearance, persistent inflammation, and defective restoration of macrophage zonation (34).

Within the fibrotic niche microenvironment, the relocation of HSCs around remodeled and enlarged vessels appears to provide instructive cues that facilitate the acquisition of KC-like features by syncytia, enabling them to capture more particles than individual KCs in their native sinusoidal setting. These findings suggest that KC-like identity can be rebuilt de novo from recruited monocytes under appropriate spatial cues (34).

Zonation also governs macrophage responses to infection. Periportal MARCO⁺ KCs restrict bacterial dissemination by capturing gut-derived microbes (39, 76), whereas pericentral macrophages become more activated in viral infections or in metabolic stress conditions (35, 44, 83). In both contexts, macrophages act as spatially anchored regulators linking local hepatocyte damage, neutrophil recruitment, and adaptive immune activation.

Altogether, these zonal macrophage circuits underscore the liver’s microanatomy as a spatially compartmentalized immune organ in which macrophage identity, function, and plasticity are continuously redefined by the architecture and metabolic gradients of the lobule.