A pharmacologic study of the relationship between lymphocyte function and surface antigen expression

The relationship between functional activity and distribution of lymphocyte surface markes has not been clearly defined. We have examined the relationship between cell surface markers and function under the influence of immunosuppressant therapy. We found that after immunization with EL₄ cells, the development of the immune reponse in the BALB/c mouse was accompanied by a decrease in spleen cells which stained brightly with fluorescein-labeled monoclonal anti-Thy 1 and an increase in cells which stained with rabbit anti-mouse Ig as measured on the FACS. Low doses of azathioprine and cyclophosphamide, which affect functional activity of the cells, do not alter cell surface markers. However, at higher doses of the drugs normalization of immunization-induced marker changes were observed, and the Thy 1⁺ and Ig⁺ surface markers were maintained at levels seen in non-immunized mice. In spite of a nearly 3-fold increase in the total number of lymphocytes and an increase in the functional activity of cytotoxic T cells (Lyt2⁺) after immunization, no alteration in the percentage of Lyt 2⁺ T cells nor in the intensity of staining with FITC-labeled Lyt 2 antibody was seen. Inhibition of the immune response with immunosuppressant also failed to change the Lyt 2⁺-staining cell population. This study demonstrates that lymphocyte functional changes precede cell surface antigen changes, and that functional changes may occur without surface antigen changes. Thus cell surface markers are late indicators of functional changes.