FIG. 1.

Homologous and heterologous responses to Gag peptides. HIV-specific CD4 responses were assessed by cytokine production at the single-cell level after short-term culture with overlapping Gag peptides, and results are shown as the proportion of total CD4⁺ T cells. Responses of HIV-2 individuals against HIV-2 Gag peptides (homologous) and of those against HIV-1 Gag peptides (heterologous) are shown, as well as the corresponding responses of an HIV-1 cohort. The total percentage of HIV-specific CD4⁺ T cells able to recognize homologous or heterologous peptide sets in each cohort (horizontally hatched bars) is illustrated in panel A. The frequencies of IL-2 single-positive (open bars) and IFN-γ single-positive (gray bars) CD4⁺ T cells and of CD4⁺ T cells that were positive for both IL-2 and IFN-γ (black bars) are also illustrated. The bars indicate the means ± the standard errors of the means. Intercohort differences were assessed using unpaired t or Mann-Whitney U tests, as appropriate, using GraphPad Prism version 4.00 (GraphPad Software Inc., SD). *, P < 0.05. The heterogeneity of the HIV-specific CD4 responses in terms of cytokine production is further defined for each responsive individual with respect to homologous and heterologous responses for the HIV-2 cohort (panels B and C, respectively) and for the HIV-1 cohort (panels D and E, respectively). HIV-2 responders are identified by uppercase letters A to S and HIV-1 responders by lowercase letters a to s. Each bar represents the total response for a given individual, with the relative contributions of cytokine-producing HIV-specific CD4 subsets indicated as above.