Annexin A1 and its membrane receptor complex: Implications for immune regulation and autoimmune disease mechanisms.

Annexin A1 (AnxA1) is a key anti-inflammatory mediator that regulates both innate and adaptive immunity, promoting resolution of inflammation and tissue repair. It is highly expressed in neutrophils, macrophages, dendritic cells, and select lymphocyte subsets, where it limits excessive immune activation and maintains immune homeostasis. Through binding to the G protein-coupled receptor formyl peptide receptor 2 (FPR2/ALX), AnxA1 induces neutrophil apoptosis and promotes macrophage polarization toward an anti-inflammatory M2 phenotype. In adaptive immunity, AnxA1 regulates CD4+ T-cell differentiation in a lineage-specific manner, promoting Th1 and Th17 responses while suppressing Th2 polarization; its deficiency skews T cells toward a Th2 phenotype with increased IL-4/IL-13 and reduced IL-17, highlighting its role in maintaining T-cell balance. In autoimmune and inflammatory disorders such as rheumatoid arthritis, lupus, type-1 diabetes, and multiple sclerosis, hyperactivation of toll-like receptor-4 (TLR4) and epidermal growth factor receptor (EGFR) drives STAT1-dependent signaling, sustaining cytokine production and tissue injury. The Annexin A2 (AnxA2)-EGFR complex further amplifies this response by downregulating AnxA1 and reinforcing pro-inflammatory signaling pathways. In contrast, AnxA1 engagement with EGFR and FPR2 redirects signaling toward STAT3, enhancing IL-10 and TGF-β production while suppressing STAT1-driven pathways. This STAT1-STAT3 balance is critical for immune resolution, inflammation control, and tissue homeostasis. Therapeutically, AnxA1-based strategies suppress STAT1 signaling and promote a regulated STAT3/SOCS3 axis associated with immune resolution, while limiting pathogenic Th17-associated STAT3 activity. Overall, AnxA1 acts as a molecular switch integrating receptor-mediated signals to fine-tune immune responses and mitigate tissue damage in chronic inflammatory and autoimmune diseases.