Equine Interleukin-10 (IL-10) is a key anti-inflammatory cytokine produced by regulatory T cells (Tregs), Th2 cells, macrophages, dendritic cells, and certain B-cell populations in horses (Equus caballus), 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, TNF-α, and IFN-γ), reduce antigen presentation, and modulate Th1-type cell-mediated responses. In equine health, IL-10 is important in regulating inflammatory conditions such as equine asthma (recurrent airway obstruction), colitis, endotoxemia, laminitis, osteoarthritis, and chronic infections including equine herpesvirus and parasitic diseases, where balanced IL-10 expression helps prevent excessive tissue damage but may also contribute to immune suppression if overexpressed. The IL-10/pro-inflammatory cytokine ratio is often used as an indicator of immune status and disease progression. In veterinary and translational research, characterization of equine IL-10 supports studies of immune tolerance, vaccine responses, respiratory and gastrointestinal inflammation, and Th1/Th2 balance. Because horses serve as valuable large-animal models for human asthma, osteoarthritis, and systemic inflammatory conditions, investigation of equine IL-10 provides comparative insight into cytokine-mediated regulation of inflammation relevant to both equine and human health.