Human erythrocytes adhering to schistosomula of Schistosoma mansoni lyse and fail to transfer membrane components to the parasite.

Abstract

We studied the adherence of human erythrocytes to larvae of the intravascular parasite Schistosoma mansoni by transmission microscopy, freeze fracture, and fluorescence techniques. In addition, we used the adherent cells to investigate the problem of host antigen acquisition. Schistosomula were cultured for from 24 to 48 h after transformation in order to clear the remnants of the cercarial glycocalyx. In some cases, the worms were preincubated with wheat germ agglutinin to promote adherence of the erythrocytes. The results were similar with and without the lectin except that more cells attached to the lectin-coated parasites. Erythrocytes adhered within a few hours and, unlike neutrophils, did not fuse with the parasite. A layer of 10-20-nm electron dense material separated the outer leaflets of the tegumental and plasma membranes. In addition, many deformed and lysed cells were seen on the parasite surface. The ability of the worm to acquire erythrocyte membrane constituents was tested with carbocyanine dyes, fluorescein covalently conjugated to glycophorin, monoclonal antibodies against B and H blood group glycolipids, and rabbit a-human erythrocyte lgG. In summary, glycophorin, erythrocyte proteins, and glycolipids were not transferred to the parasite membrane within 48 h. Carbocyanine dyes were rapidly transferred to the parasite with or without lectin preincubation. Thus, the dye in the worm membrane came from both adherent and nonadherent cells. These studies suggest that, in the absence of membrane fusion, the parasite may acquire some lipid molecules similar in structure to host membrane glycolipids by simple transfer through the medium but that B and H glycolipids and erythrocyte membrane proteins are not transferred from adhering cells to the worm.The human parasite Schistosoma mansoni lives for years within the circulation while paradoxically avoiding immune recognition and destruction. One of the mechanisms of immune evasion may be the acquisition of host antigens so that the parasite becomes a wolf in sheep's clothing (27). Supporting this theory, various host molecules have been found on the parasite, namely, Forssman antigens (7), ABH blood group glycolipids (6, 12), murine histocompatibility antigens (9,10,(23)(24)(25) complement and IgG receptors (16,27), and various serum proteins (14,28). Although the presence of these antigens has not been demonstrated to protect against immune recognition, the hypothesis is an attractive one and the methods by which these antigens are acquired merit further study.In the present work we have focused on the interaction between human erythrocytes and schistosomula. Our overall goals were to promote adherence of the cells to the worms, to characterize the adherence ultrastructurally by both transmission electron microscopy and freeze fracture, and to test whether erythrocyte membrane components were transferred to the parasite from the adhering cells. The membrane components tested were glycophorin, which was labeled covalently with fluorescein; B and ...

Schistosomula of Schistosoma mansoni use lysophosphatidylcholine to lyse adherent human red blood cells and immobilize red cell membrane components.

“…Taken together, these data suggest that ly-soPC is transferred from schistosomula to adherent RBCs, causing their lysis. Lysed RBCs adhere to schistosomula via 10-20-nm thick electron-dense plaques, but most of the ghost membrane is not directly attached to the parasite outer membrane (6). The finding that glycophorin and band 3 are completely immobilized in the adherent ghosts suggests that the entire RBC membrane is affected, in both attached and unattached regions.…”

“…Exchange of lysoPC between membranes of different cell types has been observed in other systems (48). When RBC adherence to schistosomula was promoted with lectins, lysis occuffed within 1 h (6). Close apposition of parasite and RBC membranes is apparently critical for lysis.…”

“…Paradoxically, the removal of these surface components does not produce structural alteration in the parasite membranes as seen by freeze-fracture or thinsection transmission microscopy. Unlike neutrophils, human red blood cells (RBCs) t adhering to the parasite do not fuse with the worm but lyse to form ghosts that remain attached to the parasite surface (6).…”

The lateral diffusion of lipid probes in the surface membrane of Schistosoma mansoni.

“…Furthermore, surface adsorption of probes by mechanisms other than bilayer intercalation (e.g., electrostatic interactions with phospholipid head groups) do not necessarily lead to low DE or percent recovery values. An additional point is that the schistosomula surface is known to take up host glycolipids, and this has been modeled using transfer of carbocyanin dyes from erythrocyte ghosts (5). As revealed in Fig.…”

Effect of schistosomiasis on CX3CR1‐expressing mononuclear phagocytes in the ileum and mesenteric lymph nodes of the mouse

“…S5) in the red channel. This observation can be ‘explained’ by a binding of labeled worm proteins to the red blood cell membrane . After analyzing the ileal tissue and MLNs from the mice injected with solely the fluorophore and recommended buffer, red blood cells did not show red fluorescence indicating that no background fluorescence from the conjugated fluorophore was present.…”