CD4 and hand, foot and mouth disease: Furthermore, as shown in Fig. 1c, children with severe HFMD accompanied by VEM showed a significant increase in the platelet/T cell ratio and platelet/CD4+ T cell ratio; however, there were no significant alternations in the platelet/CD8+ T cell ratio among all experimental groups, suggesting that platelets were associated with the regulation of CD4+ T cell-mediated adaptive immunity.