Immunity against Schistosoma mansoni in the mouse

Studies of the antibody-dependent killing of schistosomula of Schistosoma mansoni employing haptenic target antigens. Analysis of mechanisms responsible for the rejection of parasites in vivo

Schistosomula, surface labelled with trinitrophenyl (TNP) target antigens were tested for their susceptibility to killing by humoral- or cell-mediated anti-TNP effector mechanisms in vivo. It was found that mice passively immunized with anti-TNP serum effectively rejected an intravenous (i.v.) challenge infection with TNP-labelled schistosomula. In contrast, mice which demonstrated a strong TNP-specific, delayed hypersensitivity response to the haptenated larvae as evidenced by ear swelling, were unable to eliminate the same challenge infection. Significant passive immunization against TNP-labelled schistosomula was shown to require microlitre quantities of anti-TNP serum and could be conferred with an IgG fraction purified from the serum. The role of cells in the antibody-dependent rejection of TNP-labelled schistosomula was investigated using histopathological methods. In passively immunized mice, haptenated larvae elicited neutrophil-enriched focal reactions in the lungs and showed evidence of degeneration as early as 2 h after injection. These cellular reactions were not observed in recipients which had received prior whole-body irradiation. Nevertheless, by 24 h TNP-labelled larvae were found to have been killed in the lungs of the irradiated mice despite the absence of significant cellular attack. The above observations suggest that the antibody-dependent destruction of haptenated schistosomula results from two overlapping responses, an early response mediated by radio-sensitive cells and a second, radio-resistant response manifesting its effects at later time points. Since mice genetically deficient in the fifth component of complement fail to develop the later response, it probably reflects the effect of the lytic pathway of complement on the parasite.

Analysis of the 5q31-q33 locus shows an association between IL13-1055C/T IL-13-591A/G polymorphisms and Schistosoma haematobium infections

Millions of humans are exposed to schistosome infections, which cause severe kidney and liver disease and 280,000 deaths annually. Th2-mediated immunity is critical to human defenses against this pathogen and susceptibility to infection is controlled by a major genetic locus that includes IL4, IL5, and IL13 genes. These observations led us to evaluate whether certain polymorphisms in IL4, IL5, or IL13 determine schistosome infection. The study was performed in two Dogon villages where Schistosoma haematobium is endemic. Schistosome infections were evaluated by counting eggs and measuring worm Ags in urine. Genetic polymorphisms were determined by restriction enzyme analysis or by primer extension and denaturing high-performance liquid chromatography analysis. Associations were tested using family-based association tests and logistical regression analysis. The alleles IL13-1055C (p = 0.05) and IL13-591A (p = 0.01) are shown, by family-based association test, to be preferentially transmitted to children with the 10% highest infections. A logistic regression analysis that included IL13-1055 G/G, G/T and T/T genotypes, age, gender, and village of residency, applied to the whole study population, showed that subjects bearing the IL13-1055T/T genotype were on average much less infected than individuals with other genotypes. Previous studies on asthma indicated that the IL13-1055T allele increased gene transcription, which is in agreement with the fact that this cytokine enhances resistance to infection by schistosome in humans.

Schistosoma mansoni: inflammatory foci around larvae in the peritoneal cavity of naive mice is radiosensitive

Innate attack to Schistosoma mansoni cercariae was evaluated in irradiated mice. It was observed that 70% of the larvae from mice sacrificed one day after whole body irradiation with 400 or 800 rads were surrounded by cluster reactivities, without difference from controls. Differences were apparent on day 5 after irradiation with sub lethal (400 rads) or lethal doses (800 rads) suggesting that innate defence to infection take at least 5 days to be affected by low dose whole-body radiation.

Protective immunity to Schistosoma mansoni in mice is dependent on antibody and complement but not on radiosensitive leukocytes

The role of complement in the control of the Schistosoma mansoni infection in mice was investigated in vivo. The number of schistosomula recovered from the lung 5 days post-infection was used as a parasitological criterion of immunity. A significant difference in worm burden was observed between normal and immune mice. In contrast, when cobra venom factor (CVF) was injected into normal or immune mice 3 h before challenge, a significant increase in worm burden was noticed compared to untreated mice. We also investigated the protective mechanisms in mice that had been exposed to 650 rads of 60Co gamma radiation before challenge infection. Our results show that gamma-irradiated immune mice, depleted of more than 90% of their circulating or tissue leukocytes, are still able to destroy most of the parasites of a challenge infection with cercariae, suggesting that the radiosensitive leukocytes are not essential in the effector mechanisms of this protective immunity to S. mansoni. These results provide evidence of a role for the complement system, in association with radioresistant effector cells, in protective immunity occurring in the first hours after infection with S. mansoni.

Characterization of [3H]palmitate- and [3H]ethanolamine-labelled proteins in the multicellular parasitic trematode Schistosoma mansoni

Biosynthetic labelling experiments with cercariae and schistosomula of the multicellular parasitic trematode Schistosoma mansoni were performed to determine whether [3H]palmitate or [3H]ethanolamine was incorporated into proteins. Parasites incorporated [3H]palmitate into numerous proteins, as judged by SDS/polyacrylamide-gel electrophoresis and fluorography. The radiolabel was resistant to extraction with chloroform, but sensitive to alkaline hydrolysis, indicating the presence of an ester bond. Further investigation of the major 22 kDa [3H]palmitate-labelled species showed that the label could be recovered in a Pronase fragment which bound detergent and had an apparent molecular mass of 1200 Da as determined by gel filtration on Sephadex LH-20. Schistosomula incubated with [3H]ethanolamine for up to 24 h incorporated this precursor into several proteins; labelled Pronase fragments recovered from the three most intensely labelled proteins were hydrophilic and had a molecular mass of approx. 200 Da. Furthermore, reductive methylation of such fragments showed that the [3H]ethanolamine bears a free amino group, indicating the lack of an amide linkage. We also evaluated the effect of phosphatidylinositol-specific phospholipase C from Staphylococcus aureus: [3H]palmitate-labelled proteins of schistosomula and surface-iodinated proteins were resistant to hydrolysis with this enzyme. In conclusion, [3H]palmitate and [3H]ethanolamine are incorporated into distinct proteins of cercariae and schistosomula which do not bear glycophospholipid anchors. The [3H]ethanolamine-labelled proteins represent a novel variety of protein modification.

Cell-mediated damage to helminths

Although it is difficult to draw any sweeping conclusions that would be applicable to all helminth infections, the main features that are emphasized in this review may be summarized briefly. Pathogenic helminths, although extremely diverse in structure and behaviour, have one common feature, namely that they present to the host's defenses large, non-phagocytosable surfaces. Because of this, they are susceptible to a range of effector mechanisms differing either quantitatively or qualitatively from those that are active against other parasites or against normal or abnormal host cells. As an extreme example, the various types of cytotoxic lymphocyte, with one interesting exception, are inactive against helminths. Instead, helminth infections are characterized by high IgE responses and increased numbers of circulating eosinophils. Such eosinophils are activated, and show a marked capacity to kill a variety of target helminths in vitro. Further activation may occur in response to mast cell mediators released as a result of IgE-dependent degranulation; and IgE, as well as IgG and complement, can mediate eosinophil attachment and killing. It may therefore be suggested that the eosinophil/IgE/mast cell axis represents a powerful host defense against helminth infections. IgE can also mediate macrophage-dependent killing of several helminths, a process which involves a functional change in the macrophage, resembling activation. Although eosinophil-mediated and IgE-dependent macrophage-mediated effects are particularly potent, other effector cells are not excluded: in certain circumstances, neutrophils and conventionally activated macrophages may be equally or more effective. Neutrophils appear to act solely by oxidative killing mechanisms, whereas degranulation and the release of toxic granule contents is equally or more important in eosinophil-mediated damage. Different stages of different helminths vary in their degree of susceptibility to different mechanisms. Eosinophils appear to be somewhat less active than neutrophils against ensheathed nematodes, whereas trematodes and exsheathed nematodes are highly susceptible to eosinophil attack. In many experimental helminth infections, studies in vivo suggest a role for antibody-dependent cell-mediated immune effector mechanisms. The identity of the effector cell is difficult to establish because of a lack of techniques for specific manipulation of individual cell types, but histological studies frequently point to a strong eosinophil or macrophage involvement. The development and analysis of in vitro assays allows the study of immune effector mechanisms in man.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in glucose metabolism and cyanide sensitivity in Schistosoma mansoni during development

Schistosoma mansoni was studied by biochemical and electrophysiological techniques to follow the physiological changes occurring during transformation in the mammalian host. Volume conducted electrical potentials and measurement of CO2 evolution indicate that 3 h post-transformational schistosomula are highly sensitive to cyanide. By 24 h after transformation, evolution of CO2 under control conditions is reduced by 77% from 3 h levels, while lactate excretion rises by 84%. Cyanide does not affect the frequency or magnitude of endogenous electrical transients, but does eliminate 83% of the already reduced levels of CO2 evolved in 24 schistosomula. Electrophysiological analyses indicate that the timecourse of metabolic changes in skin- and mechanically transformed schistosomula are similar, and incubation of schistosomula in 200 micrograms ml-1 puromycin does not alter the onset of cyanide insensitivity. The adult parasite evolves a low level of CO2 which is reduced by 88% in the presence of 1 mM cyanide. No significant Pasteur effect is detected, however, and endogenous electrical activity as well as mechanical responses of the adult musculature are unaffected by cyanide exposure. Our results indicate that schistosomula continue to rely on cyanide-sensitive respiratory components for at least 3 h after transformation; by 24 h, however, the parasites are metabolically similar to the adult stage, i.e., they depend on lactate fermentation for most of their energy requirements.

Schistosoma mansoni: a comparative study of schistosomula transformed mechanically and by skin penetration. Electrophysiological responses to a wide range of substances

Volume conducted potentials were recorded from schistosomula of Schistosoma mansoni transformed mechanically (MS) and by skin penetration (SS). The spontaneous electrical activity recorded consisted of bi- and triphasic transients ranging from 20 to 200 microV in amplitude and 10 to 300 msec in duration. Low amplitude potentials occurred at a much greater frequency than large amplitude potentials, which appeared to correlate with peristaltic-like contractions of the schistosomulum's musculature. Electrical activity in the schistosomulum was highly sensitive to a number of agents believed to affect metabolic pathways, the neuromuscular system or the host/parasite interface of adult schistosomes. Among the most reactive substances were potassium antimony tartrate, eserine, poly-L-arginine and potassium cyanide. Over a wide range of experimental treatments, electrophysiological responses in schistosomula transformed from cercariae by mechanical decaudation and skin penetration were remarkably similar, supporting the notion that MS are suitable material for in vitro immunochemical, biochemical and physiological study. Some treatments, however, were more or less effective in altering electrophysiological activity and motility in the schistosomulum than in adult S. mansoni. This suggests that significant physiological alterations may occur during development from skin stage to adult parasites concomitant with immunochemical and morphological changes already known to occur.

Protection against Schistosoma mansoni achieved by immunization with sonicated parasite

Partial protection of (C57BL/6 X DBA/2)F1 mice against infection with Schistosoma mansoni has been achieved by immunization with small amounts (0.2 to 2.0 microgram) of crude cercarial sonicate adsorbed on aluminium hydroxide gel adjuvant (alum). A decrease of 34-90% in the adult worm burden, of the immunized mice, as compared to that of untreated mice or those injected with adjuvant alone, has been found in five experiments by liver perfusion six weeks after percutaneous challenge infection. High titers of anti-cercarial IgE antibodies have been found in the sera of the immunized mice by two independent techniques, radioimmunoassay and degranulation of rat basophilic leukemia cells (RBL-2H3), determined by 3H-serotonin release. By counting the live worms in the lungs of immunized and uniummized mice on days 4-7 after infection it was observed that the schistosomula were killed before they reached the lungs, probably at the skin. Mice immunized with the same amounts of cercarial antigen in Freund's complete adjuvant were not protected against infection with S. mansoni. These animals developed high titer of total anti-cercaria antibodies (determined by radioimmunoassay) but had low levels of antiparasite IgE. The possible role of IgE in protective immunity is discussed.

Decreasing immunogenicity of developing schistosome larvae

Cercariae, skin stage schistosomula, and lung stage schistosomula of Schistosoma mansoni were attenuated by gamma irradiation and tested for their ability to induce protective immunity against cercarial challenge in C57Bl/6J mice. The highest levels of resistance were induced by cercariae administered either percutaneously or intramuscularly. Skin stage schistosomula inoculated intramuscularly gave less protection while lung stage schistosomula from syngeneic donors were the least immunogenic. A similar ranking in immunogenicity was observed when the anti-skin stage schistosomular antibody responses induced by the different parasite stages were compared. In contrast, none of the immunization protocols were found to stimulate antibodies capable of recognizing lung stage schistosomula. These results suggest that, as schistosome larvae mature from the cercarial to the lung stage, they undergo a substantial loss in immunogenicity. This change may help explain the failure of older larvae to be immunologically destroyed in infected hosts.

Primary in vitro sensitization to heterogeneous soluble antigens of Schistosoma mansoni adult worms

Primary in vitro sensitization of normal mouse spleen cells was accomplished using a saline soluble heterogeneous antigenic preparation from the whole adult worms (SWAP) of Schistosoma mansoni. A SWAP-specific rosette-forming cell (RFC) assay, using antigen on sheep erythrocytes, was used to detect sensitization due to S. mansoni infection and primary in vitro SWAP exposure. The latter exposure was facilitated by SWAP adsorption to the culture vessel via poly-L-lysine. RFC expression was maximal on day 3 of culture. It was antigen-specific in regard to unexposed controls, SWAP and human gamma globulin, and as controlled by RFC detected by parallel treated (control) erythrocytes. The RFC assay was best read between 90 and 180 min after initiation of rosette formation. Assay erythrocytes gave reproducible results for at least 3 weeks after preparation.

In vitro proliferative response to living schistosomula by T lymphocytes from mice infected with Schistosoma mansoni

The development of T cell reactivity toward schistosomula during murine Schistosoma mansoni infection has been studied using an adaptation of the in vitro lymphocyte proliferation assay in which the response is elicited by exposure to living schistosomula. The reactivity measured in this system was shown to be a T lymphocyte function and to require the presence of adherent cells. This assay may therefore provide a new method for analysis of basic interactions between host cells and schistosomula. Lymph node cell responses were observed in two phases, the first of which appeared during the second week after infection, reflecting the immunogenicity of schistosome larval forms. A later, more pronounced response appeared during the chronic stage of infection, where sensitization appeared to be stimulated primarily by ongoing exposure to adult worms, rather than eggs. Lung-stage and skin-stage larvae elicited a similar degree of thymidine uptake by cells from chronically infected mice. Intact skin-stage larvae and particulate fractions provoked greater proliferation than soluble larval constituents, indicating that the lymphocyte response is directed in large part toward determinants which remain associated with the schistosomula during culture. However, the presence of major histocompatibility complex products on the membrane of lung-stage schistosomula did not influence the presentation of larval antigens to sensitized lymphocytes. The implications of these findings in immunity to schistosomiasis are discussed.

Immune evasion by Schistosoma mansoni: loss of susceptibility to antibody or complement-dependent eosinophil attack by schistosomula cultured in medium free of macromolecules

Schistosomula of Schistosoma mansoni, recovered either after penetration of cercariae through isolated rat skin or by mechanical transformation of cercariae, become fully resistant after 24-48 h of culture to damage by human blood eosinophils in the presence of human anti-schistosomular sera. Cultured schistosomula are also shown to lose their susceptibility to attack by human eosinophils in the presence of human complement. This resistance is related to the simultaneous reduction of the ability of human anti-schistosomular antibodies and human complement component C3 to bind to the surface of the cultured larvae. The development of insusceptibility to antibody, complement and eosinophil-mediated attack does not require the acquisition by the schistosomula of a protective coat of host or other macromolecules, since it is achieved in chemically defined culture medium free of serum and macromolecules. This supports the hypothesis that schistosomula undergo intrinsic changes which render them insusceptible to immune attack.

Schistosoma mansoni: age-dependent susceptibility to immune elimination of schistosomula artificially introduced into preinfected mice

Mice chronically infected with Schistosoma mansoni exhibited a significant resistance to a second infection with the same parasite, as demonstrated by their challenge worm burdens measured by portal perfusion. A decreased worm recovery was also exhibited by chronically infected mice when the challenge was administered intravenously using 3-h schistosomula obtained by the isolated skin technique or using 5-, 6-, 7- and 9-day-old schistosomula obtained from the lungs of infected donor mice. Variable results were obtained with 10- and 11-day-old forms, while schistosomula which were 12 days old or older, did not undergo significant rejection when introduced into the mesenteric veins of preinfected mice. Attempts to analyse these phenomena using the 'lung assay' were made complicated by the observation that the day of maximum recovery from the lungs was dependent upon the age of injected worms.

Parasite immunity and the major histocompatibility complex

Parasite infestations offer fertile ground for investigation of the relationship between immunity, disease and the major histocompatibility complex (MHC). However, due to the complexities of parasite life cycles and the success of parasites in evading the immune response, immune reactions against the parasite often do not parallel protective immunity, and immunity does not imply lack of disease. -- An additional level of complexity is introduced in some forms of parasite immunity by accessory effector cells, e.g., macrophages and eosinophils, that need to be 'activated' for maximal effectiveness, and the 'activated' form of these cells may partly compensate for a deficiency in specific immune responses. -- It is not surprising, therefore, that polygenic effects operate in parasite immunity and reports linking non-MHC genes with parasite immunity far out number those linking MHC genes with it. From the reports that do link MHC genes with parasite immunity, two areas emerge that are interesting. First, the increased incidence of certain HLA genes in people with schistosomiasis who develop hepatosplenic disease may pinpoint individuals at risk of morbidity and direct early treatment to them. Second, mechanisms that intimately involve MHC products but are not linked to a particular MHC haplotype, may indicate newer areas in the investigation of parasite immunity.

Studies of the antibody-dependent killing of schistosomula of Schistosoma mansoni employing haptenic target antigens. I. Evidence that the loss in susceptibility to immune damage undergone by developing schistosomula involves a change unrelated to the masking of parasite antigens by host molecules

A method was developed for coupling a hapten, trinitrophenyl (TNP), to the surface of schistosomula of Schistosoma mansoni which results in a minimal loss in their viability as judged by morphological examination in vitro and survival after injection in vivo. Skin-stage (3-h-old) and lung-stage (5-d-old) schistosomula surface labeled in this manner were then compared for their susceptibility to killing by anti-TNP antibody-dependent effector mechanisms both in vivo and in vitro. TNP skin-stage larvae were readily rejected in mice actively immunized against TNP bovine gamma globulin and were highly susceptible to anti-TNP-dependent killing mediated either by complement or purified human eosinophils in vitro. In contrast, TNP-lung-stage schistosomula, which were shown by microfluorimetry to bind anti-TNP antibody to approximately the same extent as skin-stage schistosomula, were found to be resistant to killing by the same in vivo and in vitro mechanisms. These findings suggest that the insusceptibility of postskin-stage schistosomula to antibody-dependent killing must result at least in part from an intrinsic structural change in the integument of the parasite and cannot be caused solely by the masking of parasite antigens by acquired host molecules, a mechanism of immune evasion previously proposed for schistosomes.

Recovery of Schistosoma mansoni from the skin, lungs and hepatic portal system of naive mice and mice previously exposed to S. mansoni: evidence for two phases of parasite attrition in immune mice

New or improved techniques for recovering Schistosoma mansoni from the skin, lungs and liver have enabled us to trace the attrition of a challenge infection in naive (i.e. previously uninfected) and chronically infected mice. Within each experiment, numbers of schistosomes recovered from the skin of naive mice on day 2 after challenge or from the skin and lungs on days 3, 4 or 5, did not differ significantly from the numbers recovered from the liver on days 14, 21, 28 or 35. Approximately 65% of cercariae which penetrated the skin failed to be recovered from naive mice by any of the assays and it appeared that these schistosomes had already died in the skin in the first 24 h. No further significant loss of the infection was detected in naive mice. In chronically infected mice a further attrition of the challenge infection was demonstrated in two distinct phases. An 'early phase' occurred within the first 3 days of exposure and accounted for the death of 30% of the remaining parasites. A 'late phase' occurred between days 6 and 14 and accounted for an additional 43% of deaths. Thus, the two phases of attrition accounted for a loss of approximately 73% of the infection that would have survived in a naive mice. The late phase of attrition could be demonstrated before the primary infection had matured, in contrast to the early phase of attrition which was seen only after egg laying had commenced. We believe that the early phase of attrition takes place in the skin and the late phase occurs after the schistosomes have left the lungs, either en route for the liver or as soon as they arrive in that organ. The results suggest that there are two distinct mechanisms of immunity against re-infection with S. mansoni in mice.

Factors affecting the acquisition of resistance against Schistosoma mansoni in the mouse. IV. The inability of T-cell-deprived mice to resist re-infection, and other in vivo studies on the mechanisms of resistance

CBA mice deprived of their T-cells by means of thymectomy and administration of rabbit anti-mouse thymocyte serum before a primary infection of Schistosoma mansoni, failed to resist re-infection to the same extent as immunologically intact controls. However, little difference was made to the degree of resistance to re-infection acquired by thymectomized S. mansoni-infected mice when the anti-thymocyte serum was administered after the primary infection and just before the challenge. Hydrocortisone acetate, when administered to primarily infected mice just before reinfection appeared to reduce the degree of acquired resistance, but the drug also had a schistosomicidal effect on the challenge-derived organisms. An attempt to specifically suppress the acquisition of resistance against S. mansoni by administering serum from homologously infected, resistant donors before and during the course of a primary infection failed, and partial depletion of complement activity with cobra venom factor that was administered just before challenge also failed to affect resistance. Serum obtained from mice with chronic S. mansoni infections and injected intradermally at the site of subsequent administration of a homologous percutaneous challenge infection failed to markedly inhibit maturation of the challenge in the recipient. Recipients of 3 ml of serum from heavily infected donors were also not significantly more resistant to challenge than untreated controls. However, isolated skin from heavily infected mice allowed fewer cercariae to penetrate and emerge transformed as schistosomula than did isolated skin from uninfected controls.