Cytophilic binding of IgE to the macrophage: I. Binding characteristics of IgE on the surface of macrophages in the rat

Abstract

Involvement of IgE antibody in macrophage cytotoxicity against Schistosoma mansoni schistosomula suggests a cytophilic interaction of this class of antibody with the membrane of macrophages. Peroxidase-labeled monoclonal IgE protein was used to investigate IgE-macrophage interaction in the rat. Benzidine-aggregated rat IgE bound to the surface of peritoneal macrophages under experimental conditions, preventing endocytosis of the labeled aggregates. Binding was inhibited by preincubation with unlabeled IgE (aggregated). When unaggregated IgE was used, labeling of the macrophage surface, even when endocytosis was inhibited, was also observed at 37 °C but not at 4 °C. This result indicated different binding characteristics than reported for cytophilic IgG. Radiolabeled monoclonal IgE (deaggregated by ultracentrifugation after labeling) bound to peritoneal rat macrophages at 37 °C with a maximum between 10 and 20 min and a progressive shedding thereafter, whereas no change in bound radioactivity was observed at 4 °C or after preincubation with unlabeled IgE. Radiolabeled bovine serum albumin as a control did not interact significantly with the macrophages at both temperatures in these experimental conditions. The use of ϵ-mono-specific rabbit anti-rat IgE allowed the identification of IgE on the surface of peritoneal macrophages from rats infected with S. mansoni.