FIG. 2.

Costimulation of CD45RA- or CD45RO-depleted, CD4-depleted PBL. PBL were depleted of either CD4, CD4 and CD45RA, or CD4 and CD45RO cells and stimulated with anti-CD3 and anti-CD28 MAbs. Three days following stimulation, cells were analyzed by flow cytometry for CD4 (red 613) and CD8 (allophycocyanin). CD8-expressing cells were gated, and CD4 expression was assessed. The gray histograms represent CD4 expression in unstimulated cells, and the black histograms represent CD4 expression in costimulated cells. Percentages of CD4⁺ cells in the unstimulated populations were all less than 0.2%. Percentages of costimulated CD4⁺ cells are given within the respective gates. The MFI of CD4 expression in the CD4⁺ gate is given below the respective histogram. The MFI of true CD4⁺ cells cultured in parallel was 197 (not shown).