CCR2 Enhances Anti-Intracellular Bacterial Infection by Modulating Macrophage Pyroptosis to Rebalance Th Immune...

The treatment of intracellular bacterial infections such as Chlamydia remains a significant clinical challenge due to rising antibiotic resistance and persistent, immunopathology-driven tissue damage. Macrophages are essential for host defense; they can originate from both tissue-resident precursors and circulating monocytes. During infection, macrophages at infected sites are largely derived from monocytes that migrate and differentiate there, where they phagocytose pathogens and orchestrate immune responses. The chemokine receptor CCR2 is a key regulator of this process, yet its role beyond monocyte trafficking is not fully understood. Previous studies have shown that CCR2 deficiency impairs monocyte mobilization and exacerbates disease during Chlamydia infection, shifting immune responses away from protective Th1 immunity toward pathological Th2 and Th17 polarization. Here, we investigate how CCR2 regulates macrophage function to balance protective Th1 versus pathological Th2/Th17 immunity during Chlamydia respiratory infection. Our results show that CCR2 deficiency reduces pulmonary infiltration of Ly6C^hi and Ly6C^low monocytes and shifts macrophage differentiation away from an M1-like toward an M2-like phenotype. Mechanistically, CCR2 deficiency compromises macrophage endocytosis and survival, elevates ROS production, and activates the NLRP3 inflammasome, leading to Caspase-3/GSDME-mediated pyroptosis with increased IL-1β and IL-18, while suppressing the Caspase-1/GSDMD pathway. These findings were recapitulated in vitro using C. muridarum-stimulated Ccr2-deficient bone marrow-derived macrophages (BMDMs), which also showed impaired migration, reduced M1-like polarization, diminished endocytosis, and enhanced ROS/NLRP3/pyroptosis. Furthermore, co-culture of these BMDMs with CD4⁺ T cells revealed that Th1 differentiation was inhibited, whereas Th2 and Th17 responses were promoted. Collectively, CCR2 orchestrates monocyte-macrophage function by driving M1-like polarization and inhibiting NLRP3/Caspase-3/GSDME pyroptosis to rebalance Th1/Th2/Th17 immunity, thereby enhancing bacterial clearance while mitigating immunopathological tissue damage during Chlamydia infection.