Phenotypic features of CD4^lo cells.

CD4^lo cells show phenotypic features of activated T lymphocytes. (A) CD3 expression on CD4^lo cells is lower than on CD4⁺ and CD4⁻ T cells. Bar graph of mean fluorescence intensities (mean ± SEM, n = 27) of peripheral blood lymphocytes stained with Cychrome–anti-CD4 and FITC–anti-CD3 and analyzed after setting up the regions as in a representative density plot (A inset, R1-CD4⁺, R2-CD4^lo). Statistically significant (paired ttest) differences were observed between the FITC-CD3 fluorescence intensities of CD4^lo cells (▪) and CD4⁺lymphocytes (░; *P = .022) and between CD4^loand CD3⁻ cells (■; ***P = .00004). (B-C) Lowered expression of CD4 is associated with high expression of activation antigens CD25 and HLA-DR (B and C insets show representative density plots). Bar graph in panel B shows statistically significant difference between the expression of CD4 on cells from the R2 region of the inset expressing CD25 (□) and the CD25⁻ T cells from region R1 (▪) (*mean ± SEM, n = 5, P = .0001). Panel C shows a similar difference between HLA-DR⁺ (■) and HLA-DR⁻ cells (▪; *mean ± SEM, n = 5,P = .0001). (D) The proportion of CD4^lo and CD4⁺ cells expressing CD45RA antigen was similar (bar graph), but the intensity of its expression was higher on CD4^lo cells (inset).