Minimal sulfated carbohydrates for recognition by L-selectin and the MECA-79 antibody

Sulfated forms of sialyl-Le(X) containing Gal-B-SQ, or GlcNAc-6-SO4 have been implicated as potential recognition determinants on high endothelial venule ligands for L-selectin, The optimal configuration of sulfate esters on the N-acetyllactosamine (Gal beta1-->4GlcNAc) core of sulfosialyl-le(X), however, remains unsettled. Using a panel of sulfated lactose (Gal beta1-->4Glc) neoglycolipids as substrates in direct binding assays, we found that 6',6-disulfolactose was the preferred structure for L-selectin, although significant binding to 6'- and 6-sulfolactose was observed as well. Binding was EDTA-sensitive and blocked by L-selectin-specific monoclonal antibodies. Surprisingly, 6',6-disulfolactose was poorly recognized by MECA-79, a carbohydrate- and sulfate-dependent monoclonal antibody that binds competitively to L-selectin ligands. Instead, MECA-79 bound preferentially to 6-sulfolactose. The difference in preferred substrates between L-selectin and MECA-79 may explain the variable activity of MECA-79 as an inhibitor of lymphocyte adhesion to high endothelial venules in lymphoid organs. Our results suggest that both Gal-6-SO4 and GlcNAc-6SO(4) may contribute to L-selectin recognition, either as components of sulfosialyl-le(X) capping groups or in internal structures. By contrast, only GlcNAc-6-SO4 appears to contribute to MECA-79 binding.