Which cells are major producers of IL-10 to limit immune responses?

• A. Regulatory T cells (and macrophages) produce IL-10.
• B. B cells
• C. Neutrophils
• D. Endothelial cells

Answer: (A)

IL-10 is a key anti-inflammatory cytokine that serves to dampen immune responses and prevent tissue damage. The main sources of IL-10 are regulatory T cells and macrophages. Regulatory T cells (the CD4+CD25+FOXP3+ subset) release IL-10 to suppress effector T cell activity and to limit the maturation and antigen-presenting capacity of dendritic cells. Macrophages, especially the anti-inflammatory or M2 phenotype, produce IL-10 to curb production of pro-inflammatory cytokines like TNF, IL-1, IL-6, and IL-12, and to reduce MHC II and costimulatory molecule expression on antigen-presenting cells. This combination helps terminate inflammation and restore homeostasis. While B cells can make IL-10 in certain regulatory contexts, and neutrophils or endothelial cells may produce some IL-10 endogenously, they are not the major conveyors of this cytokine, making regulatory T cells and macrophages the primary sources responsible for limiting immune responses.