CD4 and HIV infectious disease: Both acute and chronic SIV/HIV infections are associated with increases in total Treg (CD4+ Foxp3+) and CD39+ Treg (CD4+ Foxp3+ CD39+) frequencies in peripheral blood and GALT of untreated individuals which contribute to a poor effector T-cell-specific immune response, GALT fibrosis, and dysfunction and disease progression (4, 13, 14, 23, 33, 35, 36).