The distribution of CD4+ and CD4+ T cells are shown for typical samples of PBMC from HIV, aged and normal (control) donors as evaluated by flow cytometry. The cells positive for IFN-γ (PE) or TNF-α (PE) distribute vertically above the horizontal marker; the vertical distance is a relative measure of cytokine intensity. The two populations of cells that comprise the CD3 positive population are the CD8+ T cells and the CD4+ T cells (CD3+, CD8-) as shown on the X axis. The percentage of CD4+ or CD8+ T cells which contain cytokine are shown in the upper quadrants. The PBMC were activated for 15 hrs with anti-CD3 and PMA and subsequently treated as described in METHODS. In all cases, nonactivated controls (not shown) were examined; less than 0.5% of cells were cytokine positive.