SIALYLATION OF THE B-LYMPHOCYTE MOLECULE CD22 BY ALPHA-2,6-SIALYLTRANSFERASE IS IMPLICATED IN THE REGULATION OF CD22-MEDIATED ADHESION

The B cell surface receptor CD22 binds several sialoglycoproteins cont aining sialic acid in alpha 2,6 linkage, on the surface of B and T lym phocytes. Because lymphocytes adhere tightly to fibroblasts transfecte d with CD22 cDNA, it would appear reasonable to suggest that regulator y mechanisms might have evolved which prevent undesired CD22-mediated leukocyte aggregation. Here we provide evidence for the existence of a t least one mechanism that might regulate CD22 interaction with ligand s on adjacent cells. We demonstrate that sialylation of CD22 by beta-g alactoside alpha 2,6-sialyltransferase abrogates CD22-mediated lymphoc yte adhesion, and that adhesion can be restored by removal of alpha 2, 6-linked sialic acid residues from the CD22 molecule. Taken together, our results suggest that alpha 2,6-sialyltransferase can both promote and inhibit CD22-ligand interactions. These observations provide the f irst direct evidence that receptor-ligand interactions mediated by an Ig superfamily molecule are under the control of a specific glycosyltr ansferase.