Alpha-D-galactosylation of surface fucoglycoconjugate(s) upon stimulation/activation of murine peritoneal macrophages

Abstract

Murine resident macrophages express, on their surface, carbohydrate epitopes which undergo changes during their stimulation/activation as monitored by binding of 125I labelled Evonymus europaea and Griffonia simplicifolia I-B4 lectins. Treatment of the stimulated macrophages with coffee bean alpha-galactosidase abolished binding of the GS I-B4 isolectin and changed the binding pattern of the Evonymus lectin. The affinity (Ka) of Evonymus lectin for alpha-galactosidase-treated macrophages decreased approximately 23-fold, from 1.25 x 10(8) M-1 to 5.5 x 10(6) M-1. Subsequent digestion of alpha-galactosidase-treated macrophages with alpha-L-fucosidase from Trichomonas foetus, further reduced binding of Evonymus lectin. Resident macrophages showed the same pattern of Evonymus lectin binding, with the same affinity, as alpha-galactosidase-treated, stimulated macrophages. These results, together with a consideration of the carbohydrate binding specificity of the Evonymus lectin which, in the absence of alpha-D-galactosyl groups, requires alpha-L-fucosyl groups for binding, indicate the presence, on resident macrophages, of glycoconjugates with terminal alpha-L-fucosyl residues. It is also concluded that during macrophage stimulation/activation alpha-D-galactosyl residues are added to this glycoconjugate and that they form part of the receptor for Evonymus lectin. The same glycoconjugate(s) is/are also expressed on the activated macrophage IC-21 cell line which exhibits the same characteristics as that of stimulated peritoneal macrophages, i.e., it contains alpha-D-galactosyl end groups and is resistant to the action of trypsin. Both lectins were also specifically bound to Corynaebacterium parvum activated macrophages.