FUNCTIONAL-ROLE OF CD26 ON HUMAN B-LYMPHOCYTES

CD26 is a well-known activation marker on T cells and natural killer ( NK) cells [1]. It is identical with the ectopeptidase dipeptidyl pepti dase IV (DP IV). The expression of CD26 on B cells has been discussed controversially [2,3]. We have studied the expression of this enzyme o n B cells from the peripheral blood of healthy donors and of CVID pati ents, on cells of the Daudi Burkitt line and the EBV-transformed B-cel l lines Jojo and Laz509. DP IV was detected by using anti-CD26 monoclo nal antibodies and with help of specific enzyme substrates. Further th e influence of specific synthetic DP IV inhibitors on mitogenic activa tion of purified B cells and DNA synthesis of cell lines was studied. We could show that in both groups 0-5% of freshly isolated CD20-positi ve B cells do express the CD26 antigen. After stimulation with pokewee d mitogen or St. aureus protein, the fraction of CD26-positive cells w as enhanced up to 51% and 36%, respectively. Interestingly, induction of CD26 expression on B cells from CVID patients occurs in a manner si milar to the B cells from healthy donors. Treatment of peripheral bloo d B cells and B-cell lines with highly specific competitive DP IV inhi bitors leads to a significant inhibition of DNA synthesis in a dose-de pendent manner. These data show that CD26 can be considered to be an a ctivation marker not only of T- and NK cells but also of a main popula tion of B cells, suggesting an involvement of CD26 in B-cell activatio n.