Chicken Interleukin-10 (IL-10) is a key anti-inflammatory cytokine produced primarily by regulatory T cells, Th2-like CD4⁺ T cells, macrophages, dendritic cells, and certain B-cell populations in chickens (Gallus gallus), where it plays a central role in limiting excessive immune activation and maintaining immune homeostasis. IL-10 signals through the IL-10 receptor complex (IL-10R1/IL-10R2), activating JAK/STAT3 pathways that suppress pro-inflammatory cytokine production (including IL-1β, IL-6, and IFN-γ), reduce antigen presentation, and downregulate Th1-type cell-mediated responses. In poultry health, IL-10 is critically involved in modulating immune responses during infections such as avian influenza virus, Newcastle disease virus, infectious bursal disease virus, Marek’s disease virus, Salmonella spp., and Eimeria (coccidiosis), where elevated IL-10 can help limit tissue damage but may also contribute to immune suppression and pathogen persistence. The balance between IL-10 and pro-inflammatory cytokines influences vaccine efficacy, disease resistance, and growth performance in commercial flocks. As a biomarker of immune regulation, chicken IL-10 is widely studied in vaccine development, genetic selection for disease resilience, and investigations of mucosal immunity. Characterization of chicken IL-10 supports research into cytokine network regulation, host–pathogen interactions, and comparative immune tolerance mechanisms relevant to both poultry production and broader vertebrate immunology.