Effect of α-galactosylceramide (α-GalCer) on simian immunodeficiency virus (SIV) infection of macaques. Macaques were infected with SIVmac251 (control animals, n = 5, clear circles) at day 0 or administered 5 μg α-GalCer pulsed onto peripheral blood 2 days prior to SIVmac251 infection (day α-GC; n = 2, filled squares). (a) Peripheral blood NKT cell levels normalized to pre-α-GalCer NKT percentages (for animals given α-GalCer) or to peripheral NKT percentages prior to SIVmac251 infection (for control animals). (b,c,d) NKT cell subset frequencies for each subset, normalized to pre-α-GalCer or pre-infection subset frequencies, as indicated in axes. Values for red-filled squares are off-scale and are indicated above the graph. (e) SIV viraemia and (f) peripheral total CD4 T cells levels, normalized to pre-SIV infection levels were measured.