Comparison of responses by bound and free CD4 and CD8 T-cells. PBMC samples were treated with magnetic beads specific for CD4 or CD8 cells. Bound CD4 and CD8 cells (black bars) and free cells CD4 and CD8 cells (grey bars) were assayed by the IFN-γ ELISPOT assay. CD4 samples were tested against a library of 12 different peptide pools (Panel A). CD8 samples were tested under various experimental conditions against select positive peptide pools (panel B). Number of ELISPOTS/well is plotted on the Y-axis. The amount of cells placed in each well are those recovered from an original 0.5 million PBMCs.