CD4 and HIV infectious disease: To reduce potential assay variation arising from varying ratios of memory versus naïve CD4 effector cells in the suppression assay due to the selective loss of CD4+CD45RO+ memory cells in HIV infection, we isolated >95% pure effectors and Treg cells based on differential CD25 expression from within the CD4+CD45RO+ T-cell compartment (Fig. 1A).