Mallard 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 mallards (Anas platyrhynchos). 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 expression of pro-inflammatory cytokines, chemokines (including avian IL-8 homologs such as CXCLi1 and CXCLi2), and antimicrobial peptides, thereby promoting heterophil recruitment (the avian functional equivalent of neutrophils) and enhancing mucosal immunity. In healthy mallards, basal IL-17A expression is generally low but increases during bacterial, viral, and parasitic infections. Given that mallards are natural reservoir hosts for multiple influenza A virus strains, IL-17A is of particular interest in studies of avian influenza pathogenesis and immune tolerance. Characterization of IL-17A in mallards provides valuable insight into Th17-mediated immune responses, mucosal defense mechanisms, and host–pathogen interactions in wild and domestic waterfowl populations.