Anti-CD2 monoclonal antibody-induced receptor changes: down modulation of cell surface CD2

Anti-CD2 mAbs suppress T cell immunity and prolong allograft survival in vivo while inducing the down-modulation of CD2 expression. Manipulation of cell surface molecules may be important in inducing tolerance, so down-modulation of CD2 expression on T cells by anti-CD2 mAbs was further defined with an in vitro model. The anti-CD2 mAb 12-15 caused CD2 expression on purified splenic T cells to decrease from 83.4 to 22.7% total positive cells while CD3, CD4, and CD8 expression remained unchanged. The expression of other adhesion molecules, LFA-1 alpha (CD11a), LFA-1 beta (CD18), Pgp-1 (CD44), CD45, MEL-14 (L-selectin), and VLA-4 alpha (CD49d), were all increased as a result of anti-CD2 treatment, whereas CD25 (IL-2R), CD48 (CD2 ligand), and ICAM-1 (CD54) remained unchanged. Kinetics showed that CD2 down-modulation was persistent and at the same magnitude from day 1 through day 7 of culture. Anti-CD2 mAb could down modulate CD2 on both CD4 and CD8 splenic lymphocyte subsets, thymocytes, and the T cell lymphoma EL-4; and, non-T cells did not seem to participate in the process of modulation. Mechanistic studies of mAb action showed that, in addition to 12-15, other anti-CD2 mAbs could cause down-modulation of T cell CD2 expression in an epitope and isotype dependent fashion and that CD2 down-modulation correlated with inhibition of receptor-driven T cell stimulation. Intact antibody, including the Fc portion, was required to induce CD2 down-modulation, and additional experiments suggested an interaction with an Fc gamma R other than Fc gamma RII or Fc gamma RIII. CD2 down-modulation did not change with the addition of the cytokines IL-1, IL-2, IL-6, IL-10, TNF alpha, or TGF-beta 1. These results show that anti-CD2 mAbs significantly and persistently down-modulate CD2 on various T cell subpopulations. The mAbs must interact with both the CD2 receptor and an Fc gamma R. CD2 down-modulation is accompanied by changes in the array of other T cell surface receptors that may contribute to mechanisms of anti-CD2-induced immunosuppression.