The interaction between monosodium urate (MSU) crystals and immunoglobulins represents a critical regulatory mechanism in gouty inflammation. During the initial inflammatory phase, MSU crystals bind to the Fab region of IgG, forming immune complexes that activate innate immune responses. This IgG-mediated opsonization enhances crystal phagocytosis by neutrophils through Fcγ receptor engagement, leading to lysosomal enzyme release and subsequent inflammatory amplification (24). However, this pro-inflammatory effect exhibits concentration-dependent regulation, as excessive IgG adsorption on MSU crystals ultimately disrupts further immune activation through lysosomal membrane destabilization and hydrolytic enzyme release (25). The resolution phase involves a dynamic shift in MSU crystal surface protein composition. While IgG dominates during acute inflammation, high-affinity binding of apolipoprotein B (apoB) becomes predominant during resolution. ApoB competitively inhibits IgG-MSU interactions, thereby suppressing leukocyte phagocytic activity, reactive oxygen species production, and pro-inflammatory cytokine secretion. Similarly, other plasma proteins including fibrinogen and fibronectin contribute to inflammation resolution by attenuating chemokine release and leukocyte oxidative bursts. Clinical observations demonstrate a strong correlation between synovial fluid IgG-MSU deposition and elevated leukocyte counts, whereas apoB enrichment coincides with inflammatory resolution (26). These findings are further supported by experimental models showing that temporal changes in MSU crystal protein coating directly regulate the transition from pro-inflammatory to anti-inflammatory states (27).

TGF-β mediates immunosuppressive effects by inhibiting lymphocyte proliferation and antagonizing pro-inflammatory cytokines, crucial for inflammation resolution (25). Shi et al. reported that recombinant human TGF-β1 significantly reduced MSU-induced leukocyte infiltration and monocyte accumulation. TGF-β1 antagonists reversed these effects, validating its anti-inflammatory function. Additionally, MSU crystals upregulate monocyte/macrophage-derived TGF-β, suppressing neutrophil recruitment via E-selectin inhibition (25). Tumor necrosis factor α (TNF-α) is pivotal in gout pathogenesis. Busso et al. demonstrated that TNF-α blockade reduces E-selectin expression and neutrophil recruitment in MSU-induced arthritis (26). Matsukawa et al. found elevated TNF-α mRNA expression in MSU-stimulated synovial monocytes, enhancing neutrophil-mediated IL-1 release (27). Stefanie et al. revealed TNF-α-driven neutrophil activation, caspase-1 secretion, and subsequent IL-1β cleavage and activation, further amplifying inflammatory responses. Elevated TNF-α levels in GA patients’ serum and synovial fluid compared to healthy controls emphasize its clinical relevance and therapeutic potential (28).

Toll-like receptors (TLRs), located on cellular membranes, are critical pattern recognition receptors within the innate immune system. These receptors serve as vital sensors, identifying pathogenic and danger-associated molecular patterns (DAMPs). Notably, MSU crystals specifically interact with TLR2, TLR4, and the surface adapter molecule CD14. Upon binding to these receptors, MSU crystals trigger downstream signaling via the adaptor protein MyD88, leading to IL-1βrelease and neutrophil infiltration, ultimately contributing to the inflammatory cascade characteristic of gout arthritis (GA) (29, 30). NOD-like receptors (NLRs), cytoplasmic counterparts of TLRs, function as intracellular sensors recognizing endogenous danger signals as well as exogenous pathogens. Recent advances have highlighted their significant roles in the immune responses associated with GA. Specifically, the NLRP3 inflammasome, a prominent NLR family member, is activated by MSU crystals, initiating a robust inflammatory response marked by elevated production of IL-1β (31). Experimental studies using murine models indicate that mice deficient in NLRP3 fail to produce IL-1β upon exposure to MSU crystals, underscoring the essential role of this inflammasome complex in GA pathogenesis (32).

The adaptive immune system, characterized by its antigen-specific recognition, clonal diversity, and immunological memory, primarily operates through the coordinated actions of T and B lymphocytes. MSU crystals can directly participate in immune cells and contribute to gouty arthritis (GA) (33). Notably, these crystalline structures demonstrate the capacity to activate autoreactive T cell clones in an antigen-presenting cell (APC)-independent manner, suggesting a novel mechanism by which adaptive immunity may perpetuate inflammatory cascades in GA pathogenesis (34). B lymphocytes and immunoglobulins have also been implicated in GA inflammation. Studies involving B cell-deficient mice reveal that the absence of B cells substantially diminishes the inflammatory response to urate crystals. Conversely, the administration of immunoglobulin M (IgM) restores the inflammatory potential of urate, significantly amplifying the basal inflammatory state (35).

Innate immune receptors (TLRs/NLRs) stimulate autophagic activity. Stimulation of TLR4 or TLR7 promotes autophagosome biogenesis, which facilitates mycobacterial elimination (36). NLR family proteins orchestrate NLRP3 inflammasome formation, caspase-1 stimulation, and pyroptotic cell death—all negatively regulated by autophagic processes (37). The protein DRAM1 functionally connects TLR-MyD88-NF-κB cascades to selective autophagy induction (38). Within adaptive immunity, autophagy governs antigen processing (MHC I/II pathways), lymphocyte maturation, and cytokine release. Exogenous antigens undergo cross-presentation on MHC I molecules through autophagic mechanisms, whereas MHC II molecules present cytosolic antigens via peptides derived from autophagosomal compartments (39). Pathogen-derived antigens degraded within autophagosomes are transported to MHC II-loading vesicles, activating CD4⁺ and CD8⁺ T cells (39, 40). Phagocytic uptake coupled with LC3/ATG8 conjugation augments extracellular antigen presentation via MHC II (41). Additionally, γδT-cell secretion of IL-17, TNF-γ, and IL-22 is modulated by autophagy, highlighting its immunomodulatory functions (42) (Figure 1).

Elevated autophagic activity and pathway induction are observed in acute GA patients (43). In vitro, monosodium urate (MSU) crystals simultaneously stimulate NLRP3 inflammasome activation and autophagy upregulation (44). Neutrophils exposed to MSU exhibit increased LC3-II levels, an effect abolished by the autophagy inhibitor 3-MA (45). The anti-inflammatory cytokine TGF-β1 regulates autophagic flux through diverse pathways (46). Monocyte-to-macrophage differentiation during GA resolution produces TGF-β1, a pivotal mediator of inflammatory suppression (47). Autophagy exhibits dual roles in GA inflammation: While Shi et al. (48) demonstrated its inhibitory effect on MSU-induced IL-1β production, Choe et al. (49) reported that MSU-induced autophagosomes fail to degrade ubiquitinated substrates, leading to p62 accumulation and exacerbated IL-1β secretion. Therapeutic targeting of autophagy—via apoptosis modulation, immune reprogramming, or anti-inflammatory effects—holds clinical promise. Pharmacological agents, such as rapamycin, resveratrol, chloroquine) are employed in oncology, transplantation, and infectious diseases. In GA models, resveratrol counteracts MSU-mediated SIRT1 suppression in a dose-dependent manner, restoring autophagic flux and attenuating inflammation (50). SIRT1 induction represents a critical control point, positioning autophagy modulators (activators or inhibitors) as viable therapeutic options (Table 1).

Etanercept, a recombinant fusion protein comprising the extracellular ligand-binding region of human TNF receptor 2 coupled to IgG1-Fc, exhibits superior TNF-α binding capacity compared to endogenous receptors. This biologic agent sequesters soluble TNF-α, preventing receptor engagement and subsequent proinflammatory signaling, while the Fc moiety enhances pharmacokinetic stability. Clinical evidence from Tausche et al. (51) describes a refractory GA patient showing no response to conventional therapies, including colchicine, NSAIDs, steroids, and opioids. Twice-weekly subcutaneous etanercept markedly decreased flare frequency, tender joint count and inflammatory markers. A separate case by Zhang et al. (52) involved a 48-year-old male with treatment-resistant tophaceous gout, hypertension, and infected ulcers. Following etanercept initiation, rapid symptomatic relief preceded full ambulatory recovery by 14 d, with normalized CRP/ESR and serum urate. Long-term febuxostat/colchicine therapy achieved tophi clearance within 12 months without disease recurrence. Adalimumab, as a human IgG1 monoclonal antibody targeting TNF-α, demonstrates an extended plasma half-life and lacks immunogenic animal-derived epitopes. Sumiyoshi et al. (53) detailed its application in a 39-year-old male with HLA-B27–associated reactive arthritis secondary to C. trachomatis infection, superimposed on chronic gout. Despite maximal anti-inflammatory therapy, disease progression occurred. Combination therapy with sulfasalazine and biweekly adalimumab induced prompt clinical remission. Serial ultrasonography confirmed complete resolution of synovial and tendinous inflammation by 12 months (53).

Infliximab exhibits high specificity for transmembrane TNF-α. Upon binding, it triggers cell lysis through complement-dependent cytotoxicity (CDC) and antibody-dependent cellular phagocytosis (ADCP). Fiehn and Zeier (54) reported its therapeutic application in a 44-year-old male with refractory gouty arthropathy and secondary renal amyloidosis. Symptomatic recurrence at six weeks necessitated repeat infusion, which again induced prompt clinical resolution. Maintenance therapy demonstrated excellent tolerability with durable therapeutic effects.

The humanized monoclonal antibody tocilizumab (TCZ) targets both soluble and membrane-bound IL-6 receptors, effectively disrupting downstream gp130 signaling cascades. Clinical evidence demonstrates its therapeutic potential in treatment-resistant gout cases. Pinto and colleagues (55) reported on a 44-year-old male patient with advanced tophaceous gout who exhibited poor response to conventional therapies, including colchicine, allopurinol, and diclofenac. Although monthly tocilizumab (TCZ) infusions at a dose of 8 mg/kg were effective in preventing acute gout flares, they did not lead to a marked reduction in tophus burden (55). In a separate case described by Mokuda et al. (56), a 61-year-old woman with concomitant gout and renal dysfunction achieved complete clinical remission following TCZ treatment administered every four weeks at the same dosage. The intervention resulted in normalization of inflammatory biomarkers, including C-reactive protein and ferritin, and sustained disease control over a 24-week period, despite prior failure of colchicine combined with prednisone. Calvo-Aranda and Sanchez-Aranda (57) reported favorable therapeutic outcomes following tocilizumab (TCZ) treatment in a 56-year-old male patient with refractory gout and coexisting metabolic conditions, including hypertriglyceridemia and hyperferritinemia, after inadequate response to prior anakinra therapy. The treatment achieved rapid symptom control with maintained efficacy throughout 12 months of follow-up, exhibiting an excellent safety profile. Pers et al. (58) evaluated tocilizumab (TCZ) in elderly rheumatoid arthritis patients, finding that while it was well tolerated, its efficacy was lower compared to younger patients. Despite this, TCZ led to sustained clinical improvement over 6 months with good tolerability. In a prospective study, Latourte et al. (59) assessed the efficacy of tocilizumab (TCZ) in 11 patients with calcium pyrophosphate deposition (CPPD) disease who had shown resistance to multiple therapeutic agents, including colchicine, nonsteroidal anti-inflammatory drugs, corticosteroids, and anakinra. Both intravenous and subcutaneous regimens showed universal clinical improvement by 3 months, with durable responses maintained through 10 months of follow-up. The treatment was generally well-tolerated, with only three reported adverse events.

Recent studies suggest that dysbiosis of the gut microbiota may modulate systemic inflammation and urate metabolism, offering a novel perspective on GA pathogenesis (60). Gut microbes influence purine metabolism by regulating the synthesis of purine-metabolizing enzymes (61). Patients with gout often exhibit decreased levels of Faecalibacterium prausnitzii and Bifidobacterium, both known for their anti-inflammatory properties and short-chain fatty acid (SCFA) production (62, 63). SCFAs such as butyrate inhibit histone deacetylases (HDACs), promoting regulatory T cell (Treg) differentiation and attenuating NLRP3 inflammasome activation (64, 65). Moreover, fecal microbiota transplantation (FMT) and probiotic supplementation have demonstrated preliminary success in reducing systemic inflammation and uric acid levels in experimental models (66). These findings underscore the therapeutic potential of microbiota modulation in GA management.

Epigenetic alterations, including DNA methylation, histone modifications, and non-coding RNA expression, critically regulate gene transcription in immune and metabolic pathways implicated in GA (67). Hypermethylation of promoter regions in anti-inflammatory genes such as IL-10, and hypomethylation in pro-inflammatory loci, such as TNF, have been identified in patients with chronic gout (68). Histone acetylation is particularly relevant: reduced histone H3 acetylation at the FOXP3 locus compromises Treg cell function and amplifies joint inflammation (69, 70). Inhibitors targeting epigenetic enzymes, such as DNA methylation, have shown potential immunosuppressive and uric-lowering effects (71, 72). Additionally, microRNAs (miRNAs), especially miR-155 and miR-146a, modulate TLR/NF-κB signaling and IL-1β secretion in GA, further supporting the role of non-coding RNA-based regulation (73–76).