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

Abstract

Human buffy coat cells adhering to schistosomula of Schistosoma 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 four fluorochromeconjugated 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 #m in diameter, were seen on the parasite surface. In addition, the fluorochromes were observed in granules within the cells. Electron microscope autoradiography of worms preincubated with 1251-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. In addition, 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. It is concluded that 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. Presumably, the components of the parasite surface which have originally bound the ligands are also endocytosed since surface components labeled by galactose oxidase and NaBaH4 are taken into cells when examined by light microscope autoradiography. Finally, membrane fusion occurs in areas devoid of multivalent glands, which suggests that these ligands serve to bring the cells and parasites close together; but the actual fusigens probably reside in the lipids in the outer tegumental membrane.Schistosomula, larvae of Schistosoma mansoni, can be destroyed in vitro by human eosinophils--but not by neutrophils--after the parasites are preincubated in heat-inactivated sera from patients with schistosomiasis (28). Eosinophil-mediated killing is caused by exocytosis of lysosomes onto the parasite surface (3,7,17), and subsequent damage to the tegumental membrane is caused by major basic protein (2) and possibly peroxidases to which the worm is quite sensitive (13). The neutrophils, on the other hand, do not exocytose their lysosomes but instead fuse their plasma membranes with the outer tegumental membranes of the schistosomula over areas as large as 8 #m in diameter (3).In these experiments, we have promoted adherence between human buffy coat cells and schistosomula with three lectins concanavalin A (Con A), wheat germ agglutinin (WGA), and lentil lectin (Len), as well as with IgG purified from a hyperimmu...

Evidence that the reduced surface antigenicity of developing Schistosoma mansoni schistosomula is due to antigen shedding rather than host molecule acquisition

“…Simple exposure of parasites to either lung fragments for 3 h or fresh NMS for 30 min failed to reduce surface antigenicity, indicating that simple contact with host tissue or serum factors does not constitute the stimulus. Potentially, exposed epitopes could be cleaved by host enzymes, phagocytosed by host granulocytes (Caulfield et al 1982) or lost as some function of the close interaction of migrating schistosomula with the vascular endothelium (Wheater & Wilson 1979). Alternatively, antigen shedding may occur in response to some physiological condition not provided by the culture medium.…”

Excretory–secretory products of helminth parasites: effects on host immune responses

“…Another potential mechanism by which the shedding of surface components of a trematode parasite may contribute to immune evasion has been described for schistosomula of S. mansoni. Caulfield, Korman & Samuelson (1982) proposed that endocytosis of surface-derived antigens of S. mansoni schistosomula by human neutrophils could inhibit some of the cells' functions (discussed below). Badley et al (1987) investigated the relationship between the ES antigens, shedding of surface molecules and immune responses to the infective larvae of T. canis.…”

“…The gut-associated ES products of adult schistosomes are significant components of the circulating immune complexes and these are possible contributors to immune-complex blockading of eosinophil cytotoxicity. Surface components of S. mansoni schistosomula, which are shed into in vitro ES products (Samuelson, Sher & Caulfield, 1980;Samuelson, Caulfield & David, 1982), are endocytosed by human neutrophils (Caulfield et al 1982). This process may serve to remove antibody from the surface, possibly inhibiting eosinophil-mediated killing, and may prevent neutrophils from discharging their lysosomes at the parasite surface (Caulfield et al 1982).…”

“…Surface components of S. mansoni schistosomula, which are shed into in vitro ES products (Samuelson, Sher & Caulfield, 1980;Samuelson, Caulfield & David, 1982), are endocytosed by human neutrophils (Caulfield et al 1982). This process may serve to remove antibody from the surface, possibly inhibiting eosinophil-mediated killing, and may prevent neutrophils from discharging their lysosomes at the parasite surface (Caulfield et al 1982). In this manner endocytosis of surface components of schistosomula could contribute to the inability of neutrophils to mediate cellular cytotoxicity in contrast to eosinophils (Vadas, David, Butterworth, Pisani & Siongok, 1979).…”

The cercarial glycocalyx of Schistosoma mansoni.

“…Transmission Microscopy: Parasites were fixed in mixed aldehydes for 30 min on ice (22), postfixed in osmium for 90 min on ice, stained en bloc with uranyl acetate for 2 h at room temperature, dehydrated, and embedded (50). Some parasites were preincubated with 1 mg/ml IRS or NRS for 1 h at room temperature, and washed four times before fixation in mixed aldehydes (4). Alternatively, parasites were fixed in glutaraldehyde containing ruthenium red (30) or tannic acid with or without 0.5 mg/ml saponin (34), and postfixed with osmium.…”