ACTIVATION SIGNALS ARE DELIVERED THROUGH 2 DISTINCT EPITOPES OF CD100, A UNIQUE 150-KDA HUMAN LYMPHOCYTE SURFACE-STRUCTURE PREVIOUSLY DEFINED BY BB18-MAB

We have previously reported the identification of a glycoprotein dimer , now termed CD100, at the lymphocyte cell surface using a mAb termed BB18. In the present study we isolated a second mAb, termed BD16, reco gnizing another epitope of this 150 kDa structure. We show that intera ction with individual mAb triggers differential functional effects on peripheral blood lymphocytes (PBL) and purified T cells. In particular and of the utmost interest, BD16 mAb strongly inhibits CD3 induced PB L proliferation while it dramatically increases the CD2 induced prolif eration. In contrast, after T cell purification, BD16 mAb increases bo th CD2 and CD3 induced proliferation. It has to be noted that perturba tion of the same 150 kDa surface molecule with BB18 mAb exerts no effe ct on CD2 and CD3 induced proliferations, while inducing a strong lymp hocyte proliferation in the presence of submitogenic concentrations of phorbol myristate acetate.