Overall CD4⁺ T cell functionality is decreased after SIV infection. Flow cytometric analysis of SEB-stimulated memory and effector (CD28⁺CD95⁺ and CD28⁻CD95^+/−) CD4⁺ T cells by production of CD40L, IFNγ, IL-2, TNFα, or a combination. (A) Pie charts represent fraction of cells that have 4 (yellow), 3 (cyan), 2 (blue), or 1 (purple) function(s). P value represents partial permutation test. (B) Delineation of the 15 possible cytokine combinations is shown for SIV− (green) and SIV+ (black). Dots represent individual RM responses. (C) Student t test results between SIV− and SIV+ cytokine responses corresponding to panel B. Pink shading represents a significant P value less than .05. (D) Total frequency of cytokine producing memory and effector CD4⁺ T cells for SIV⁻ (green) and SIV+ (black) RMs in response to SEB stimulation. P values represent partial permutation test results (A) or Student t test results (C). SEB responses from uninfected animals are based on data from group 1 and group 3 animals before SIV infection.