Regulatory role of IgE binding factors from rat T lymphocytes. V. The carbohydrate moieties in IgE-potentiating factors and IgE-suppressive factors

IgE-binding factors were formed by incubation of Con A-activated cells with IgE, and the nature of the carbohydrate moieties in these factors was assessed by measuring their affinity for Con A, peanut agglutinin (PNA), and Limulus polyphemus agglutinin (LPA). it was found that IgE-suppressive factors formed by 1 μg/ml Con A-activated cells had affinity for PNA but did not bind to either Con A or LPA. The presence of tunicamycin during their biosynthesis affected neither the affinity of the factors for PNA nor their biologic activity. These results suggest that IgE-suppressive factors have an O-glycosidically linked oligosaccharide containing β-glycosidically linked galactose as a terminal residue. By contrast, IgE-potentiating factors formed by 10 μg/ml Con A-activated cells bound to Con A, lentil lectin, and LPA. The removal by neuraminidase of sialic acid in the potentiating factors resulted in loss of their biologic activity. When the 10 μg/ml Con A-activated cells were cultured with IgE in the presence of tunicamycin, the IgE-binding factors formed in the culture no longer bound to Con A or the lentil lectin, and selectively suppressed the IgE response. The results indicate that IgE-potentiating factors contain a N-glycosidically linked mannose-rich oligosaccharide. However, the IgE-binding factors formed in the presence of tunicamycin retained their affinity for LPA. Furthermore, neuraminidase treatment of the factors generated in the presence of tunicamycin resulted in loss of their affinity for LPA and the appearance of affinity for PNA, with persistence of IgE-suppressive activity. The biologic activity of the latter factors after neuraminidase treatment and their affinity for lectins are identical to those of IgE-suppressive factors. The results indicate that IgE-potentiating factors have not only N-glycosidically linked oligosaccharide but also O-glycosidically linked oligosaccharide, and that the former sugar side chain is essential for their biologic function. Intracellular IgE-binding factors were detected in both 10 μg/ml Con A-activated cells and 1 μg/ml Con A-activated cells after incubation with IgE for 4 hr, when no IgE-binding factors were detectable in the culture fluid. Intracellular IgE-binding factors lacked affinity for all of the lectins studied and neither enhanced nor suppressed the IgE response.