Simultaneous regulation of CD2 adhesion and signaling functions by a novel CD2 monoclonal antibody

Accessory molecules on T cells can support adhesion and transduce agonistic signals that facilitate Ag receptor-induced T cell activation. The T cell differentiation Ag CD2 may exert both functions, as has been amply demonstrated in studies with CD2 mAbs. In addition, experiments in which either purified ligand (CD58) or transfected CD2 and CD58 molecules were used have confirmed this notion. However, controversy exists as to whether CD2 alters its affinity for CD58 in the course of T cell stimulation, and whether this putative affinity change affects CD2-mediated activation signals. We now describe a CD2 mAb (HIK27) that recognizes an epitope constitutively expressed on resting T cells and induces increased adhesiveness of CD2 toward CD58. Addition of HIK27 to a stimulatory but nonmitogenic pair of CD2 mAbs induces a strong proliferative response. Finally, HIK27 was found to be co-mitogenic with CD58 expressed on sheep erythrocytes, B cell lines, and CD58-transfected L cells. The simultaneous modulation of CD2 adhesion and signaling on HIK27 binding suggests that both functions of the molecule may be enhanced in the course of T cell stimulation.