[In vitro study of immunologic phenomena in humain and experimental schistosomiasis. I. Comparative in vitro study of the lethal activity of immune serums on the immature and adult forms of Schistosma mansoni]

Schistosoma mansoni-specific rat T cell clones. II. Different effects of adult worm-specific T cell clones in immunocompetent and nude infected rats

The in vivo functional activities of two highly proliferating helper rat T cell clones (E23 and G5) specific for the excretory-secretory antigens of Schistosoma mansoni adult worms were investigated. When injected into infected immunocompetent rats, both clones increased the antibody response against the 30-40-kDa schistosomulum surface antigens, but failed to induce an immune protection. In contrast, when the same clones were injected into infected nude rats, a high degree of protection was obtained. In this latter case the absence of detectable specific antibody response, whether of IgE or IgG isotype, suggested that parasites were destroyed by an antibody-independent mechanism, i.e. macrophages activation by lymphokines. Indeed supernatants obtained from T cell clones specifically restimulated with schistosome antigens expressed a macrophage activated activity similar to interferon-gamma. Following incubation with these supernatants or with the active fractions, macrophages exhibited a significant schistosomulicidal activity and both clones were shown to transfer an antigen-specific delayed-type hypersensitivity reaction to normal rats. Taken together these results demonstrate that, depending on the immune status of the host, antigen-specific T cell clones can function differently and consequently that one function associated with one type of lymphokine could be favored.

Helper T cells induced by a purified 28-kilodalton antigen of Schistosoma mansoni protect rats against infection

Schistosoma mansoni adult worm 28-kilodalton (kDa) proteins were separated on polyacrylamide slab gels, recovered by electrophoretic elution, and used to immunize Fischer rats. After the second or third injection, inguinal lymph node T lymphocytes were propagated in vitro for 4 weeks in the presence of syngeneic antigen-presenting cells and adult worm antigens in medium containing interleukin-2. After this period of culture, 99% of the cells expressed the W3/13+ surface phenotype and 93% of the cells expressed the W3/25+ surface phenotype. These cells were then tested for their in vivo functional activity after transfer to Fischer rats that had been either infected with S. mansoni cercariae or immunized with the 28-kDa purified protein. In each case, an increase of S. mansoni-specific antibodies was observed. Whereas anti-28-kDa antibodies were only detectable at day 40 postinfection in controls injected with normal T lymphocytes, they appeared as early as day 13 postinfection when the animals received 28-kDa protein-specific T lymphocytes. This led to an effective protection of infected rats (45 to 85%) which correlated with the increase in S. mansoni-specific antibodies. These results therefore demonstrate that the 28-kDa protein possesses epitopes capable of activating helper T cells, which confer a strong protective immunity by enhancing the production of cytotoxic antibodies. The stimulation of the 28-kDa-specific T cells with recombinant proteins suggests that the major epitopes are located toward the carboxylic end of the molecule.

Functional study of a monoclonal antibody to IgE Fc receptor (Fc epsilon R2) of eosinophils, platelets, and macrophages

An IgM mAb (BB10) was produced by immunization of mice with human eosinophils purified according to their abnormal low density ("hypodense" cells), and previously shown to exhibit increased IgE-dependent antiparasite cytotoxicity. This BB10 antibody, selected for positive fluorescence staining of hypodense blood or lung eosinophils and low or negative staining of normodense eosinophils or neutrophils, could strongly inhibit IgE-dependent cytotoxicity of human eosinophils and platelets. The specificity for the IgE Fc receptor was suggested by the high levels of inhibition of IgE rosettes formed by eosinophils after incubation with the purified IgM fraction of BB10, whereas other receptors (Fc gamma R, CR1) were not affected. On the other hand, BB10, able to inhibit rat eosinophil Fc epsilon R, did not react with the IgE Fc receptor on mast cells or basophils. A technique using radioiodinated BB10 allowed us to quantify the specific binding of BB10 to human eosinophils and platelets. Competition experiments revealed a crossinhibition between the binding of BB10 and IgE, suggesting the specificity of BB10 for the IgE binding site of eosinophil, platelet, and monocyte Fc epsilon R. Three proteins having extrapolated Mr of 32,000, 43,000-45,000, and 97,000 were found in the platelet extract eluted from a BB10 or from an IgE immunosorbent column. These findings confirm the similarities between IgE Fc receptors on human eosinophils, platelets, and macrophages, already observed with polyclonal antibodies directed against the B lymphocyte Fc epsilon receptor. They suggest, moreover, that the mAb BB10 can represent a good reagent for further investigations on the structure and the functions of this IgE Fc receptor (Fc epsilon R2).

Occurrence of fibronectin antigenic determinants on Schistosoma mansoni lung schistosomula and adult worms

Fibronectin determinants were revealed in a soluble extract of Schistosoma mansoni adult worms by standard immunodiffusion and immunoelectrophoresis techniques. The same target molecules were demonstrated on the parasite's surface using a binding assay with [125I] anti-fibronectin. The use of fluorescein- and peroxidase-conjugated-antibodies confirmed the above observations and provided a fairly precise means for locating the cross-reacting antigen on the worm surface. An in vitro cytotoxic assay using inactivated (56 degrees C, 2 h) anti-fibronectin rabbit immune serum and guinea-pig serum as a source of complement was developed. In these conditions, anti-fibronectin exerted cytotoxic activity against lung schistosomula and adult worms but not skin schistosomula. The ultrastructural damage induced by anti-fibronectin in the presence of complement was studied using transmission electron microscopy. The results suggest a close association between fibronectin determinants and S. mansoni membrane.

Rat IgE directed against schistosomula-released products is cytotoxic for Schistosoma mansoni schistosomula in vitro

The immunogenicity of molecules shed by schistosomula into culture medium (antigens present in schistosomula-released products, SRP-A) has been studied. The results obtained show that SRP-A preferentially induce an IgE response when injected into rats, without the need for adjuvants. Moreover, anti-SRP-A IgE is cytotoxic in vitro for the larvae in the presence of macrophages, eosinophils or platelets, which have previously been demonstrated as being the three efficient killer cells for schistosomula in the presence of specific IgE. Immunofluorescence analysis locates the target antigens at the schistosomulum surface. Among the antigens recognized by anti-SRP-A IgE, two molecules of 26 and 22 kDa have been identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by western blotting.

Interactions between eosinophils and antibodies: in vivo protective role against rat schistosomiasis

An original protocol of cell transfer from Schistosoma mansoni-infected rats to normal recipient rats is used to investigate the protective role of phagocytic cell populations, described as effector cells in vitro, against a challenge infection with S. mansoni. Nonadherent, eosinophil-enriched and -adherent, macrophage-rich cell preparations, injected via intradermal and subcutaneous routes at the precise site of exposure to cercariae, were able to significantly protect the recipient rats. The time-course study of this protective effect according to the time after infection of donor rats revealed that eosinophils were the major cell population involved in the early phase of infection (4 to 5 weeks), whereas macrophages could also be incriminated thereafter. A rosette assay using anti-immunoglobulin-coated erythrocytes indicated a sequence of the various antibody isotypes under study (IgG1, IgG2a, IgE) on the eosinophil surface, during the course of infection. As previously shown in vitro, cytophilic antibodies seemed to participate in the protective effect of eosinophils, since eosinophil-enriched cells from normal rats, sensitized in vitro with immune complexes present in infected rat serum, could also confer significant protection. These observations establish therefore the relevance between our previous in vitro studies and rat resistance to a challenge infection with S. mansoni, underlining the major role played by the interaction between antibodies and phagocytic cells (eosinophils and macrophages).

Neutral protease activities at different developmental stages of Schistosoma mansoni in mammalian hosts

Neutral protease activities of schistosomula, 20 day old and adult worms of S. mansoni have been studied. 1. The neutral enzymes of the three development stages are able to hydrolyse numerous natural and synthetic substrates. 2. The enzymes of homogenates and saponin CaC12 extracts show significant discrepancies in their specificities, optimum pH activities and in the effects of enzyme inhibitors. 3. A serine protease activity was specific for the schistosomula stage whereas thiol proteinases characterize the later stages of evolution. A metalloaminopeptidase activity was shown at all three stages. 4. Gel filtration chromatography and isoelectric focusing of an adult worm homogenate demonstrated the presence of at least 5 caseolytic and 4 azocollytic neutral activities. Three aminopeptidases, one of which exhibited iminopeptidase specificity were revealed by the same procedure.

Schistosomiasis from S. mansoni in mice: the relationship between acquired immunity and serum levels of lethal antibody

Acquired immunity to Schistosoma mansoni induced by a primary infection with cercariae of one or both sexes was assessed in mice by the recovery of parasites of a challenge infection from the lungs or the liver. In addition, the antibody-dependent complement-mediated cytotoxicity against schistosomula in vitro was titrated in sera obtained from both groups of animals. The degree of immunity as detected by the lung recovery technique in mice infected with a mixture of male and female cercariae was variable and lower than 50%. In contrast, no immunity was observed in the group of animals infected with 40 'single-sex' cerariae. The titre of lethal antibody in a pool of sera firm these animals was about 10, whereas it was about 640 in a pool of sera from bisexually infected animals. Lethal antibody titres ranged from 20 to 120 for unisexual infection and 240 to 1920 for bisexually infected mice. In some cases a significant degree of immunity was detected by liver perfusion in mice with a primary unisexual infection. However, the lethal antibody titre of sera from mice with a 'single-sex' infection remained low, even when the immunity was apparent.

Proteolytic cleavage of IgG bound to the Fc receptor of Schistosoma mansoni schistosomula

After the binding of IgG to the surface Fc receptor of Schistosoma mansoni schistosomula, the Fab portions of IgG are cleaved and small peptides are liberated in the culture medium. At least two types of proteinase activities have been demonstrated in the secretory products of schistosomula. One is an endoprotease with trypsin-like activity, with an optimum pH of 7 and an optimum temperature of 45 degrees C. The other is a metalloaminopeptidase with an optimum pH of 7 and temperature of 37 degrees C.

In vitro study of immunological events in human and experimental schistosomiasis: relationships between cytotoxic antibodies and circulating Schistosoma antigens

Complement-dependent cytotoxic antibodies were found in 54% of Schistosoma mansoni infected patients from Burundi and in 69 to 78% of Schistosoma mansoni ninfected Brazilian patients. The levels of cytotoxic Ab were not statistically different in sera from infected mothers and from their newborn children, suggesting a transfer through the placenta. A sandwich radioimmunoassay (SRIA) and the Radioimmunoprecipitaion-PEG assay (RIPEGA) technique were used in order to detect respectively total schistosome circulating soluble antigens (CSA) and schistosome antigen '4' in sera from infected patients. An inverse relationship was found between the presence of cytotoxic Ab and both total CSA and antigen '4'. The cytotoxic Ab and total CSA levels were followed in five Erythrocebus patas monkeys for 30 weeks after Schistosoma mansoni infection. As in human schistosomiasis the presence of cytotoxic Ab was found to be inversely correlated with the presence of total CAS. The blocking role of Schistosoma mansoni antigens in a complexed form was suggested by the inhibitory effect of the ultracentrifugation pellet of infected human serum on the cytotoxic activity. Moreover, the CSA absorption of infected monkey serum by passage through an anti-CSA immunosorbent significantly increased the cytotoxic activity. Possible mechanisms for the inhibitory role of circulating immune complexes on complement-dependent cytotoxic activity are discussed.

Eosinophil-dependent cytotoxicity in rat schistosomiasis. Involvement of IgG2a antibody and role of mast cells

Using Schistoma mansoni schistosomula collected in vitro and sensitized with 42-day-infected rat serum, normal rat peritoneal cells enriched in eosinophils were proven to subsequently adhere to and kill the schistosomula within 24 to 48 h. The cell-dependent, heat-stable antibody in infected rat serum reached a peak between 30 and 42 days after infection. Inhibition experiments with aggregated immunoglobulins indicated the role of IgG2a antibody in the adherence of eosinophils to sensitized schistosomula. The immune absorption technique showed that IgG2a antibody was involved in the mechanism of cytotoxicity of effector to target cells, whereas the role of IgE antibody could be excluded. Ultrastructural studies revealed the constant presence of eosinophils and mast cells in contact with schistosomula. The use of purified cell populations showed that the cytotoxic effect of the original cell population was significantly decreased after depletion of mast cells and partially restored after addition of mast cells. These observations, together with those concerning the role of IgE immune complexes in macrophage cytotoxicity, suggest the possible participation of anaphylactic antibodies in immunity to schistosomes in the rat.

Inhibition of lymphocyte proliferation by factor(s) produced by Schistosoma mansoni

Normal spleen cells of CBA mice or Fischer rats were cultured with mitogens or allogeneic cells, together with various substances of Schistosoma mansoni origin, and thymidine uptake was measured. The proliferation (DNA synthesis) of normal lymphocytes was inhibited by the incubation product of the parasite as well as by cell-free supernatant of schistosome culture. Inhibition was obtained only when active materials were added at the beginning of the culture. Both T and B cell proliferation were inhibited. The inhibitory activity found in cell-free supernatant suggested the release by the parasite of some factor(s) interfering with lymphocyte proliferation. Moreover, serum from rats infected by S. mansoni inhibited lymphocyte proliferation also. The inhibitor(s) appeared heat resistant, dialyzable and of low molecular weight (500-1000). Incubation of normal spleen cells with S. mansoni inhibitor(s) did not enhance the release of nonspecific suppressor cell factor. The inhibition of product(s) released by the parasite could explain part of the immunosuppression status found in schistosomiasis.

[Immunologic reaction in parasitic invasion (author's transl)]

Among the manifold immunologic events which take place during parasitic invasions, production of autoantibodies and immune complexes can play a serious role during infections with African and American trypanosomes. The importance of complement deserves new attention. The increasing level of IgE induced by helminthic infections on a humoral basis seems to be caused by separate worm allergens; its involvement in self-cure phenomena together with processes on cellular levels is discussed. Destructive processes on various development stages of schistosoma and immunological events during cutaneous leishmaniasis are also cell mediated. Variations in the antigenic behaviour of parasites and their immunological mimicry by uptake of substances from the host and their immunosuppressive action are discussed. As reasons for absence of immunity against animal parasites this action can disturb either humoral or cellular immunological procedures or both.

Drugs as ligands of immunogenic molecules in parasites: an approach to the isolation of target-antigens

Schistosomicide drugs are used as ligands to isolate the target antigens of schistosome by affinity chromatography. Anti-target antigens immune sera produced in rabbit permit their localization on the parasite using immunofluorescence. Target antigens of some drugs determine a relatively high immunoprotection in rat or mouse schistosomiasis infection.

Cross-immunity to Schistosoma mansoni and S. haematobium in the hamster

Hamsters (WO strain) with a primary infection of Schistosoma mansoni or S. haematobium rapidly developed immunity to homologous challenge judged by the lung recovery assay. Immunity was detected at 4-5 weeks and reached a plateau 6 weeks after infection. Using this information, hamsters with an 8-week primary infection with S. mansoni or S. haematobium were tested for resistance to homologous reinfection and resistance to a challenge with the other species of schistosome. Primary infection with S. mansoni or S. haematobium conferred a high level of immunity to reinfection with either species of schistosome judged by the perfusion assay, involving recovery of adult worms 6-10 weeks following challenge. Estimation of the level of immunity with the lung recovery assay, 5 days after challenge, indicated that immunity due to a primary infection with S. mansoni acted at or before migration of the challenge through the lungs but immunity stimulated by a primary S. haematobium infection was only partially effective at the lung stage and substantial destruction of challenging organisms occurred at a later stage of development. Antibodies in immune sera of hamsters with a primary S. mansoni or or S. haematobium infection were shown to bind to common antigens on the surface of young schistosomula of either species by u.v. microscopy using as detecting agent a fluorescein-labelled rabbit antiserum directed against hamster globulins.

A role for the eosinophil in acquired resistance to Schistosoma mansoni infection as determined by antieosinophil serum

Partial immunity to schistosomiasis mansoni has been demonstrated in mice and has recently been transferred passively with serum, but not with cells. In vitro studies using human and rodent materials have demonstrated antibody-dependent cell-mediated damage to immature schistosomes (schistosomula); the cell involved in some of these in vitro systems appears to be the neutrophil and in others the eosinophil is suspected. In the present study the effect of antileukocyte sera on partial immunity to schistosomiasis was tested in vivo using quantitative assay systems for schistosomula in the lungs and adult worms in the portal venous system. Mice infected with 10 cercariae of Schistosoma mansoni 16 and 32 wk before challenge with 500 cercariae showed reductions in the recovery of schistosomula at 4 and 6 days of approximately 40%; adult worm recovery was reduced by 60%. Treatment with antilymphocyte, antimacrophage, or antineutrophil serum had no effect on the numbers of schistosomula recovered from the lungs of immune animals, but in the mice treated with antieosinophil serum the numbers of schistosomula and adult worms recovered increased to the levels seen in normal nonimmune animals. Furthermore, sera collected from the partially immune mice and passively transferred to uninfected mice conferred a marked resistance to infection as measured by recovery of schistosomula; this was also abrogated by treatment with antieosinophil serum. These studies suggest that antibody-dependent cell-mediated immunity to schistosomiasis occurs in vivo, and also establishes a role for the eosinophil in immune systems.