We have recently published an article which appears to be of relevance to this recurrent discussion. J Immunol Methods 2001 Aug 1;254(1-2):1-12. Coexpression of CD4 and CD8alpha on rat T-cells in whole blood: a sensitive marker for monitoring T-cell immunosuppressive drugs. Diaz-Romero J, Vogt G, Weckbecker G. Department of Transplantation, Preclinical Research, Building 386/628, Novartis Pharma AG, Lichstrasse 35, CH-4002 Basel, Switzerland. The aim of this study was to develop a new quantitative method for measuring in vitro the effects of T-cell immunosuppressive drugs by flow cytometry. Rat whole blood samples were stimulated with the T-cell mitogen succinylated concanavalin A in the presence or absence of different drugs. After 3 days, the expression of CD25 and CD8alpha in mitogen-stimulated CD4(+) cells increased 10- to 20-fold as measured by flow cytometry. Drug efficacy and potency was calculated based on dose-response curves of the drug-mediated decrease in CD4(+)/CD8alpha(+)/CD25(+) cells. The expression of CD8alpha in mitogen-stimulated CD4(+) cells was blocked completely by calcineurin inhibitors (cyclosporine A and FK-506), and partially by rapamycin and SDZ-RAD. The IC(50) (50% inhibitory concentration) values obtained were (mean+/-S.E.): 99.5+/-16.6 nM for cyclosporine A, 10.4+/-1.3 nM for FK-506, 1.8+/-0.7 nM for rapamycin, and 6.4+/-1.1 nM for SDZ-RAD. Our results show, for the first time, that CD8alpha, used as an activation antigen, is a sensitive marker for monitoring T-cell immunosuppression. Jose
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