CD3 AND CD2 LIGATION ALTERS CD49D EPITOPE EXPRESSION

The combination of anti-CD2 plus anti-CD3 monoclonal antibodies (mAbs) synergistically prolongs allograft survival and induces antigen-speci fic tolerance, Since altered expression of cell surface molecules migh t be important for tolerance induction, the effect of anti-CD2 and ant i-CD3 mAbs on the expression of adhesion molecules was analyzed on spl enic T cells with an in vitro model, The anti-CD2 mAb, 12-15, alone ha d no effect on the expression of integrin alpha 4-chain epitopes recog nized by two anti-CD49d (VLA-4 alpha) mAbs, R1-2 and PS/2. The anti-CD 3 mAb, 2C11, caused R1-2 epitope expression to decrease, while PS/2 ep itope expression remained unchanged. The combination of anti-CD2 and a nti-CD3 mAbs further decreased R1-2 epitope expression while preservin g PS/2 epitope expression. The expression of integrin beta 1 and beta 7 chains, each of which form heterodimers with alpha 4 chains, also re mained unchanged, Expression of other integrin, selectin, or immunoglo bulin superfamily molecules (CD11a, CD18, CD44, CD45, CD48, CD54 and C D62L) were all significantly increased by anti-CD2 or anti-CD3 mAbs. D ecreased R1-2 epitope expression was anti-CD3 dependent and specifical ly augmented by anti-CD2 mAb. CD2-regulated decreases in R1-2 epitope expression correlated with increased cAMP and could be prevented by ad dition of high doses of IL-2 but was not affected by the addition of o ther cytokines, R1-2 alpha 4 epitope expression could be specifically restored by the divalent cation Mn2+, which also increased functional binding to the VCAM-1 ligand, Significantly, the R1-2 but not the PS/2 mAb prolonged graft survival in a cardiac allograft model. These resu lts show that anti-CD2 and anti-CD3 mAbs selectively decrease integrin alpha 4 chain epitope expression on T cells through conformational re gulation. Decreased expression of a CD49d epitope is unique in compari son to the up-modulation of other T-cell adhesion receptors, These cha nges correlate with functional effects and provide an additional mecha nistic explanation for the synergistic effect of anti-CD2 plus anti-CD 3 in producing tolerance.