Interaction between IgE complexes and macrophages in the rat: a new mechanism of macrophage activation

In earlier studies we found that normal rat macrophages, preincubated at 37 degrees C with the serum of syngeneic rats immune to Schistosoma mansoni, strongly adhered to S. mansoni schistosomules whereas no significant adherence was induced with serum from normal rat. Using 51 chromium release assay, it now proved that immune serum-incubated macrophages lysed the schistosomules in 18 h. Absorption experiments and ultracentrifugation of the immune serum showed that immune complexes containing specific IgE antibody against S. mansoni and soluble parasite antigens induced macrophage adherence and cytotoxicity. Using various labeling techniques, the binding of aggregated rat IgE to the macrophage surface at 37 degrees C is evident in conditions where endocytosis is neglible. The binding of immune complexes containing IgE antibody to S. mansoni elicits dramatic ultrastructural changes in the macrophage and an increase of its lysosomal enzymes together with specific lytic activity for the schistosomules. The parallel development of immune serum-induced macrophage adherence or cytotoxicity with the level of circulating IgE antibody to the parasite in correlation with the development of immunity in the rat, suggests that this new mechanism of macrophage activation could play a role in immune effector mechanisms against S. mansoni. Therefore, IgE acts as a humoral mediator of cellular immunity.