Human neutrophils endocytose multivalent ligands from the surface of schistosomula of Schistosoma mansoni before membrane fusion.

Open Access
Publisher Website
Google Scholar
Abstract
Human buffy coat cells adhering to schistosomula of S. mansoni that were preincubated in fluorochrome-conjugated concanavalin A (Con A), wheat germ agglutinin, lentil lectin or purified IgG from a hyperimmunized rabbit, were examined by fluorescence and transmission electron microscopy and by freeze-fracture. All 4 fluorochrome-conjugated multivalent ligands were homogeneously distributed on the parasite surface after preincubation. Within 1-3 h after the addition of cells, large areas of nonfluorescence, 10-20 .mu.m in diameter, were seen on the parasite surface. The fluorochromes were observed in granules within the cells. EM autoradiography of worms preincubated with 125I-Con A showed silver grains evenly distributed over the tegumental membrane. After the addition of cells, grains were seen over phagolysosomes in the cytoplasm of neutrophils adhering to the parasites. No grains were present over large areas of the tegumental membrane, which still retained its normal architecture, or over fusions between the neutrophil plasma membrane and the outer tegumental membrane. Rabbit IgG formed an electron-dense layer on the tegumental membrane which was endocytosed by neutrophils. Both neutrophils and eosinophils fused with the parasite in areas containing no electron-dense material on the surface. Human neutrophils will endocytose a variety of multivalent ligands from the surface of schistosomula, which probably accounts for the failure of neutrophils to kill the parasite and acts to clear the parasite surface of both antigen and antibody. The components of the parasite surface which have originally bound the ligands are also endocytosed since surface components labeled by galactose oxidase and NaB3H4 are taken into cells when examined by light microscope autoradiography. Membrane fusion occurs in areas devoid of multivalent glands. Apparently these lignads serve to bring the cells and parasites close together; the actual fusigens probably reside in the lipids in the outer tegumental membrane.