GM-CSF potentiates macrophages to retain an inflammatory feature from their circulating monocyte precursors in...

Peripheral monocytes represent an important source of macrophages in the synovium of rheumatoid arthritis (RA). However, it remains unclear whether the proinflammatory traits in RA monocytes can be maintained during their differentiation into macrophages without exogenous polarization stimuli.

Peripheral blood CD14⁺ monocytes from RA patients and healthy controls (HCs) were differentiated into macrophages in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) or macrophage colony-stimulating factor (M-CSF). Transcriptomic analysis, metabolic profiling, flow cytometry, and functional assays were performed.

Transcriptomic and functional analyses revealed that GM-CSF-differentiated macrophages (GM-DMs) from RA monocytes preserved a proinflammatory M1-like phenotype, whereas M-CSF-differentiated macrophages (M-DMs) lost this phenotype. Synovial GM-CSF expression levels were significantly elevated in RA patients compared to HCs and were positively correlated with disease activity (DAS28-CRP). In contrast, M-CSF expression levels were reduced and inversely correlated with DAS28-CRP. RA GM-DMs exhibited hyperactivation of the STAT5 signaling and a hypermetabolic profile, characterized by enhanced oxidative phosphorylation (OXPHOS) and impaired glycolysis. Strikingly, CCL22 was identified as the most upregulated chemokine in RA GM-DMs. Elevated synovial CCL22 expression strongly correlated with M1 macrophage infiltration and disease activity. Functionally, CCL22 promoted CD4⁺ T cell migration and skewed differentiation toward Th1 and Th17 subsets, but not regulatory T cells (Tregs), in RA patients.

GM-CSF supports the maintenance of the proinflammatory nature of RA monocyte-derived macrophages, driving CCL22-mediated T cell responses. This study highlights the GM-CSF/CCL22 axis as a pathogenic mechanism in RA and suggests CCL22 as a novel potential therapeutic target.