Expression of IL-2 receptor subunit p55 (CD25) on normal human lymphocytes

Unstimulated peripheral blood lymphocytes of normal Saudi Arabian males were examined for the expression of IL-2 receptor subunit p55 (IL-2Rp55) by two-color flow cytometric analysis using monoclonal antibodies. Eighteen percent of the normal lymphocytes were positive for this marker. Approximately 84% of the IL-2Rp55+ cells were CD3+ T cells of which CD4+ and CD8+ T cell subsets constituted 75 and 13%, respectively. CD19+ B cells made up 12% of the IL-2Rp55+ lymphocytes. In the pan T cell population 20% cells were IL-2Rp55+, whereas among the B cells 16% cells were IL-2Rp55+. In the CD4+ and CD8+ T cell population IL-2Rp55+ cells were 29 and 7% respectively. In comparison, normal Caucasian male population had significantly higher proportions of IL-2Rp55+ lymphocyte subsets, the total IL-2Rp55+ lymphocytes being 33 +/- 10%. However, except for CD8+ T cells, there was no difference in the mean phenotypic values of IL-2Rp55+ cells between the two populations. The present findings clearly show a significant expression of IL-2Rp55 (CD25) on peripheral blood lymphocytes in normal, healthy Saudi Arabian blood donors and Caucasians. It is suggested that the baseline values of IL-2Rp55+ lymphocytes must be established for the local normal population before the expression of this marker is implicated either as an active immune response or as an immune disorder.