Sialylation of the sialic acid binding lectin sialoadhesin regulates its ability to mediate cell adhesion

The macrophage-specific cell surface receptor sialoadhesin. which is a memb er of the newly recognized family of sialic acid binding lectins called sig lecs, binds glycoprotein and glycolipid ligands containing a2-3-linked sial ic acid on the surface of several leukocyte subsets. Recently, the sialic a cid binding activity of the siglec CD22 has been demonstrated to be regulat ed by sialylation of the CD22 receptor molecule. In the present work, we sh ow that desialylation of in vivo macrophage sialylconjugates enhances sialo adhesin-mediated lectin activity. Herein, we show that receptor sialylation of soluble sialoadhesin inhibits its binding to Jurkat cell ligands, and t hat charge-dependent repulsion alone cannot explain this inhibition. Furthe rmore, we show that the inhibitory effect of sialic acid is partially depen dent on the presence of an intact exocyclic side chain, These results, in c onjunction with previous findings, suggest that sialylation of siglecs by s pecific glycosyltransferases may be a common mechanism by which siglec-medi ated adhesion is regulated, (C) 1999 by The American Society of Hematology.