IL17A and hand, foot and mouth disease: Previous reports have shown that abnormal changes in Th1, Th2, Th17, T follicular helper (TFH), and T regulatory (Treg) cells and associated cytokines such as interleukin (IL)-6, IL-17A, IL-21, and tumor necrosis factor alpha (TNF-α) are all involved in the pathogenesis of EV71-associated HFMD [4, 13–16].