Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine that plays a central role in regulating immune responses and maintaining immune homeostasis. It is primarily secreted by immune cells, including regulatory T cells (Tregs), macrophages, dendritic cells, and B cells, and functions as a master regulator of inflammation. Structurally, IL-10 is a glycoprotein that exists as a non-covalent homodimer, with each subunit comprising 178 amino acids and a molecular weight of approximately 18 kDa.

IL-10 mediates its effects through the IL-10 receptor complex, which consists of IL-10 receptor α (IL-10Rα) and IL-10 receptor β (IL-10Rβ) subunits. This interaction activates intracellular signaling pathways, predominantly the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway, particularly STAT3. This signaling cascade drives the transcription of genes that suppress inflammatory responses, including the inhibition of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-12 (IL-12). Additionally, IL-10 downregulates the expression of major histocompatibility complex (MHC) class II molecules and co-stimulatory molecules on antigen-presenting cells, further dampening immune activation.

Functionally, IL-10 serves as a critical regulator of immune balance by preventing excessive inflammation and promoting tissue repair. It achieves this by modulating the activity of macrophages and dendritic cells, limiting their ability to produce pro-inflammatory mediators and present antigens. IL-10 also promotes the differentiation and stability of Tregs, enhancing immune tolerance. Furthermore, it supports wound healing processes by reducing tissue-damaging inflammation and stimulating fibroblast activity. However, the immunosuppressive properties of IL-10 allow it to play a dual role in cancer, where it contributes to immune evasion by tumors within the tumor microenvironment.