Chicken IL-17A (Interleukin-17A) is a pro-inflammatory cytokine belonging to the IL-17 family that plays an important role in host defense and inflammatory responses in chickens (Gallus gallus). IL-17A is produced primarily by Th17-like CD4⁺ T cells, 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 the expression of pro-inflammatory cytokines, chemokines (including CXCLi1 and CXCLi2, the avian functional homologs of IL-8), and antimicrobial peptides, thereby promoting heterophil recruitment (the avian equivalent of neutrophils) and enhancing mucosal and barrier immunity. In healthy chickens, basal IL-17A expression is generally low but increases during bacterial, viral, and parasitic infections, including Eimeria spp. (coccidiosis), Salmonella spp., avian influenza virus, and infectious bursal disease virus (IBDV). In poultry immunology research, chicken IL-17A serves as a key biomarker of Th17-type immune activation and inflammatory responses, providing insight into host–pathogen interactions, vaccine-induced immunity, and regulation of mucosal defense mechanisms in commercial and experimental poultry systems.