Surface expression of antigens participating in stimulation.

Surface expression of antigens participating in stimulation differentiates CD4^lo lymphocytes from the CD4⁺population. Panels show representative density plots of expression of CD4 versus CD28 (A), CD152 (B), and CD95 (C), and insets illustrate the comparison and statistical evaluation (mean ± SD) of the proportions of cells showing respective phenotypes within the CD4⁺ (■) and CD4^lo (▪) populations. Samples from 5 people were analyzed in each group. Asterisks indicate the significance of observed differences at P = .0001 (A, ***, n = 16), P = .043 (B, *, n = 10), andP = .005 (C, **, n = 12).