IL17A and parasitic infectious disease: In the early stage of a parasitic infection, the levels of host CD4+ and CD8+ T cells are increased, and Th1 or Th17 immune response is the mainstay, which exerts anti-parasitic effects by secreting interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), or interleukin-17 (IL-17).