CD4 and Zika virus infectious disease: Similar to what we observed in the peripheral blood, ZIKV infection induced a CD4+ T cell response in the spleen with a significant increase in both the frequency and number of antigen-experienced (CD11a+CD49d+) CD4+ T cells (Fig 4A–4E), compared to UV-inactivated virus- and mock-infected mice (27% versus 12% and 11%, respectively).