Figure 1.

Involvement of macrophages in the development of rheumatoid arthritis. Macrophages produce cytokines that support inflammation by recruiting new immune cells (monocytes), polarizing T cells, and activating fibroblasts. Activated fibroblasts secrete receptor activator of nuclear factor kappa-B (NF-κB) ligand (RANKL) and macrophage colony-stimulating factor 1 (M-CSF), which induce osteoclast differentiation, which is enhanced by TNF and other cytokines. The formed autoimmune complexes, in turn, activate macrophages. Macrophages are also affected by cytokines produced by T cells, fibroblasts, and innate immune cells.