Interleukin- 17A as an Immunomodulatory Cytokine in Animal Health and Diseases: A Systematic Review

Interleukin-17A (IL-17A), a pro-inflammatory cytokine primarily produced by Th17 cells, has emerged as a pivotal immunological mediator in both protective and pathological processes across different animal species in addition to human beings. Over the past decade, research has expanded significantly, elucidating IL-17A's roles in host defense, immune modulation, disease progression and vaccine induced immune responses. The present review focuses on recent advances in the understanding of IL-17A within the context of veterinary medicine. IL-17A has been implicated in protection from various diseases as well as in their pathogenesis in different contexts. Different diseases like bovine mastitis, bovine tuberculosis, canine immune-mediated hemolytic anemia, avian viral infections and many others, the raised expression of IL-17A helps predict how mild or severe a case will be. Diagnostic potential has been demonstrated, particularly in cattle, where IL-17A serves as a promising biomarker for mycobacterial infections and inflammatory responses. In vaccination, recombinant and plasmid-based IL-17A delivery has enhanced immune protection against pathogens such as bovine herpesvirus and Marek's disease virus in poultry, suggesting utility as a novel adjuvant. Furthermore, studies in swine and poultry have revealed age- and tissue-specific dynamics of IL-17A during immune maturation and infection. While IL-17A contributes to immunopathology in some contexts, it also holds promise for advancing vaccine development, diagnostics, and targeted immunotherapy in veterinary practice. The shared role of IL-17A in veterinary and human health highlights the need of a One Health approach, acknowledging the interdependence of human, animal and environmental well-being. Understanding IL-17A's function across species can reveal cross-species therapeutic strategies and vaccination programs, promoting a holistic approach to manage inflammatory and infectious diseases. Further, research into IL-17A's mechanisms and its modulation could lead to more effective treatments and prevention strategies, benefiting both human and animal health. This review highlights critical discoveries, emerging tools and future directions to harness IL-17A for improving animal health, productivity and disease control strategies in both livestock and companion animals.