Equine IL-17A (Interleukin-17A) is a pro-inflammatory cytokine belonging to the IL-17 family that plays a central role in host defense and inflammatory responses in horses (Equus caballus). IL-17A is produced primarily by Th17 cells, as well as by γδ T cells and other innate lymphoid populations, in response to microbial infection and immune stimulation. It acts on epithelial, endothelial, and stromal cells to induce expression of pro-inflammatory cytokines, chemokines (such as CXCL8), and antimicrobial peptides, thereby promoting neutrophil recruitment and enhancing mucosal and barrier immunity in the respiratory, gastrointestinal, and reproductive tracts. In healthy horses, basal IL-17A expression is generally low, but levels increase during bacterial and fungal infections, parasitic disease, and inflammatory conditions. Elevated IL-17A has been implicated in equine asthma (recurrent airway obstruction), inflammatory airway disease, endometritis, and other neutrophil-driven inflammatory disorders. In veterinary and comparative medicine research, equine IL-17A serves as an important biomarker of Th17-mediated immune activation and neutrophilic inflammation, providing insight into disease pathogenesis, vaccine responses, and potential immunomodulatory therapeutic strategies in equine health.