A CARBOHYDRATE STRUCTURE ASSOCIATED WITH CD15 (LEWIS(X)) ON MYELOID CELLS IS A NOVEL LIGAND FOR HUMAN CD2

The T cell and NK cell adhesion molecule CD2 interacts with different ligands, viz, CD58, CD48, and CD59, Using a fluorescent multimeric con struct of rCD2, we previously identified an additional CD2 ligand (CD2 L) on the erythroleukemic cell line K562, CD2L bound to a different re gion of CD2 than known ligands and was N-glycosylation dependent, In t his study we show that mAbs specific for the carbohydrate Ag Lewis(x) (CD15, Gal-beta 1-4 GlcNAc alpha 1-3Fuc) inhibit multimeric rCD2 bindi ng to CD2L, CD2L is restricted in expression to myeloid cells, where i t is co-expressed with CD58 on monocytes and is the dominant, if not s ole, CD2 ligand on neutrophils, Sugar specificity studies show that CD 2L is not CD15, Thus, whereas soluble Lewis(x) inhibits binding of CD1 5 mAb to K562 and neutrophils, binding of multimeric rCD2 is unaffecte d, Furthermore, multimeric rCD2 binding to K562 is inhibited by L-fuco se and following treatment of K562 with an alpha 1-6 fucosidase, where as these treatments do not inhibit the binding of CD15 mAb, Thus, it i s likely that CD2L is a carbohydrate structure closely associated with , yet distinct from, CD15, which can be sterically blocked by CD15 mAb , Functional studies revealed that CD2L is probably an important CD2 l igand in the non-MHC-restricted NK cell killing of K562 target cells, since this activity was strongly inhibited by CD15 mAb, Collectively, this study indicates that a CD15 (Lewis(x))-associated carbohydrate st ructure(s), which has previously been shown to be a selectin ligand, a lso may function as an important CD2 ligand on myeloid cells.