The article reviews the biology of interleukin-10 (IL-10), a key anti-inflammatory cytokine. IL-10 is produced by various immune cells, including monocytes/macrophages, T cells, and B cells, and plays a crucial role in regulating immune responses. It acts through a transmembrane receptor complex composed of IL-10R1 and IL-10R2, and influences the functions of many immune cells. IL-10 inhibits the production of inflammatory mediators and antigen presentation by monocytes/macrophages, while enhancing their scavenger and tolerance-inducing functions. It also suppresses the activation and proliferation of T cells, particularly Th1, Th17, and Th2 cells, and promotes the development of regulatory T cells (Treg) and Tr1 cells. IL-10 is involved in the regulation of immune responses in various diseases, including autoimmune disorders, chronic inflammatory conditions, and infections. The article discusses the molecular mechanisms of IL-10 signaling, including its interaction with the Janus kinase (Jak) family and STAT transcription factors, and its role in modulating immune responses through various pathways. IL-10 is also important in maintaining immune homeostasis and preventing excessive immune reactions that can lead to tissue damage. The article highlights the importance of IL-10 in both health and disease, and suggests that modulating IL-10 activity could be a potential therapeutic strategy for chronic infections and inflammatory diseases.The article reviews the biology of interleukin-10 (IL-10), a key anti-inflammatory cytokine. IL-10 is produced by various immune cells, including monocytes/macrophages, T cells, and B cells, and plays a crucial role in regulating immune responses. It acts through a transmembrane receptor complex composed of IL-10R1 and IL-10R2, and influences the functions of many immune cells. IL-10 inhibits the production of inflammatory mediators and antigen presentation by monocytes/macrophages, while enhancing their scavenger and tolerance-inducing functions. It also suppresses the activation and proliferation of T cells, particularly Th1, Th17, and Th2 cells, and promotes the development of regulatory T cells (Treg) and Tr1 cells. IL-10 is involved in the regulation of immune responses in various diseases, including autoimmune disorders, chronic inflammatory conditions, and infections. The article discusses the molecular mechanisms of IL-10 signaling, including its interaction with the Janus kinase (Jak) family and STAT transcription factors, and its role in modulating immune responses through various pathways. IL-10 is also important in maintaining immune homeostasis and preventing excessive immune reactions that can lead to tissue damage. The article highlights the importance of IL-10 in both health and disease, and suggests that modulating IL-10 activity could be a potential therapeutic strategy for chronic infections and inflammatory diseases.