Specific ligation of surface alpha-D-galactosyl epitopes markedly affects the quantity of four major proteins secreted by macrophages.

Activated macrophages (M phi s) have terminal alpha-D-galactosyl (alpha D-Gal) residues on their membranes that are not apparent on resting cells. Ligation of these epitopes with Griffonia simplicifolia I-B4 (GSI-B4), a lectin that has specificity for alpha-D-Gal residues, alters selected M phi functions. To explore the mechanism(s) that may be responsible for some of the functional changes, alterations in the secretory pattern of [35S]methionine-labeled proteins were assessed when cells were cultured with or without this ligand. The proteins were identified by Western blots and quantitated. Interestingly, alpha-D-Gal ligation proved to decrease the secretion of some proteins while increasing the secretion of others. Some of the most significant changes were observed in four proteins: fibronectin and transglutaminase were down-regulated by 55 and 66% respectively, while plasminogen activator inhibitor type 2 was increased by 259% and collagenase was increased 1000-fold. These observations show that the emergence of new oligosaccharide epitopes, such as alpha-D-Gal, concomitant with M phi activation may serve to mediate the transduction of signals that cause quantitative changes in the elaboration of diverse M phi products. The biologic significance of the four identified proteins has been well established. Fluctuations in their levels are likely to play a role at sites of chronic inflammation.