FIG. 4.

CD4⁺CD25⁺-mediated suppression of CD8⁺ IFN-γ production in acute FIV infection occurs after 21 days pi. FACS-purified CD8⁺ cells from FIV⁺ cats were stimulated with Con A for 18 h then cocultured with autologous CD4⁺CD25⁺ cells at a ratio of 0.5:1 (CD4⁺CD25⁺ to CD8⁺) and IFN-γ production was determined by ELISpot. The gray shaded bars represent CD8⁺ cells alone and the black bars represent CD8⁺/CD4⁺CD25⁺ cocultures with each pair of bars representing an individual cat. There is significant CD4⁺CD25⁺-mediated CD8⁺ suppression in six of seven cats at days 28–56 pi (p < 0.05). CD8⁺ suppression was not evident during the first 21 days of infection (not shown).