ANTIBODY-BINDING PROFILE OF PURIFIED AND CELL-BOUND CD26 - DESIGNATION OF BT5 9 AND TA5.9 TO THE CD26 CLUSTER/

The CD26 activation antigen (Ag) which is expressed on a subpopulation of human T cells has been characterized as dipeptidyl peptidase IV (D PP IV, EC 3.4.14.5). In this paper, we describe the antibody binding p rofile of CD26/DPP IV, purified from human peripheral blood lymphocyte s. The purified molecule binds to the anti-Ta1, anti-1F7 and anti-134- 2C2 monoclonal antibodies (mAb), reported to react with cell-bound CD2 6 Ag. Among unclustered mAb recognizing T cell antigens, two, anti-BT5 /9 and anti-TA5.9 were found to react with purified and cell-bound CD2 6 Ag. The classification of the BT5/9 Ag, the functional properties of the BT5/9+ T cell subset, as well as the in vivo effect of anti-BT5/9 mAb administration, are re-interpreted in the light of its specificit y. Applying the anti-TA5.9 mAb in three color FACS analyses, we demons trated that CD26+bright cells co-express CD45RO but not HLA-DR and CD3 8.