CD4 and immunodeficiency disease: The macaques with high setpoint SIV viral loads (SIVhi; n = 8; mean: 6.2 log RNA copies per ml plasma; range: 5.0-7.7) had a greater loss of CD4+ T cells (mean: 776 per μl blood; range: 236-1360) and TFH cells and inverted CD4/CD8 ratios, showing severe immunodeficiency or “severe SIV infection”, as compared to those with low setpoint viral loads (SIVlow; n = 6; mean: 3.4; range: 2.0-4.7) and higher CD4+ T cells (mean: 1316; range: 954-2214) (Figure S1), or “mild SIV infection”.