IgE antibody in eosinophil- and macrophage-mediated in vitro killing of Dipetalonema viteae microfilariae.

The current study describes the effect of different cell types on Dipetalonema viteae microfilariae in vitro in the presence of immune rat serum. Microfilariae were killed by eosinophil-rich cell populations and antibodies. The serum factor that mediated adherence and cytotoxicity was nonopsonizing and heat labile but was not complement, as there was neither binding of C3 molecules on the surface of D. viteae microfilariae obtained from cultures of adult females nor significant adherence of cells to the surface of the parasite at any dilution of fresh normal rat serum. Immunoadsorption and inhibition experiments showed that the adherence-promoting activity resides in the IgE class of antibody. Microfilariae killing by eosinophil-rich peritoneal exudate cells (PEC) was probably not entirely due to eosinophils because the percentage of mortality was not reduced by a gradual decrease in the eosinophil concentration in cell suspensions and was not related to a particular eosinophil-parasite ratio. The time course studies of adherence and subsequent analysis by electronmicroscopy demonstrated that eosinophil adherence occurred at an early stage of incubation and was followed by a macrophage adherence mediated by the same antibody isotype. The early-stage eosinophil adherence and subsequent degranulation onto the surface of microfilaria did not kill the target but apparently immobilized the parasite. The late-stage adherence of macrophages was associated with the appearance of lysosome-like granules in the cell and with the destruction of the parasite. The immune adherence to D. viteae microfilariae was markedly parasite specific, since there was no cross-reaction between antibodies induced by infection of rats with D. viteae or Trichinella spiralis in mediating adherence and cytotoxicity by effector cells.