A cyclic AMP inducible gene expressed during the development of infective stages of Trypanosoma cruzi

By using a subtractive hybridization strategy, we have identified a gene (TC26) that is expressed in metacyclic and tissue culture derived trypomastigotes of Trypanosoma cruzi but not log stage epimastigotes and is induced during the differentiation of metacyclic stages in vitro. In contrast, the TC26 transcript is absent from stationary phase epimastigotes of a strain that fails to undergo metacyclogenesis under the same culture conditions. Transcription of TC26 can be induced in epimastigotes by incubation with cyclic AMP and cyclic AMP analogues but it is inhibited by activators of cAMP dependent phosphodiesterases. Cyclic AMP fails to enhance tubulin gene expression in the same parasites. While present in the genome in multiple copies, the TC26 gene is expressed as a single mRNA species of approximately 5 kb. Computer analysis of the sequence of a 650-bp cDNA clone revealed no significant homologies at either the nucleotide or amino acid levels with other known proteins. Possible roles for the TC26 gene product in metacyclogenesis are discussed.

Interleukin 5 is required for the blood and tissue eosinophilia but not granuloma formation induced by infection with Schistosoma mansoni

Eosinophils are thought to play a major role in the immunobiology of schistosomiasis. To investigate the immunologic basis of the eosinophil response and directly assess the function of eosinophils in egg-induced pathology, mice infected with Schistosoma mansoni were injected with a monoclonal antibody produced against interleukin 5 (IL-5), a cytokine previously shown to stimulate eosinophil differentiation in vitro. This treatment suppressed the generation of eosinophil myelocyte precursors in the bone marrow and reduced to background levels the numbers of mature eosinophils in the marrow, in circulation, and within acute schistosome egg granulomas. Nevertheless, granulomas in the anti-IL-5-treated/eosinophil-depleted mice at 8 weeks of infection were only marginally smaller than those in animals injected with control monoclonal antibody, and hepatic fibrosis was comparable in the two groups. Additional parameters such as worm burden, egg output, and serum IgE levels were unaltered by the anti-IL-5 treatment. In contrast, infected animals injected with monoclonal antibody against gamma interferon (IFN-gamma) displayed circulating eosinophil levels that were elevated with respect to control mice, possibly because of an enhanced release of mature eosinophils from the marrow, and developed egg granulomas that were indistinguishable in size and cellular composition from those in control animals. Immunologic assays revealed that lymphocytes from acutely infected mice produce large quantities of IL-5 but minimal IFN-gamma when stimulated with either egg antigen or mitogen. Taken together, these results indicate that neither IL-5 nor eosinophils are essential for egg-induced pathology but suggest that lymphocytes that belong to the IL-5-producing TH2 subset predominate during acute infection and may induce granuloma formation by the production of other cytokines.

Schistosome vaccines: current progress and future prospects

Vaccination against human schistosomes in laboratory hosts is now a reality. A number of different parasite molecules have been shown to confer partial protective immunity against challenge infection with Schistosoma mansoni or Schistosoma japonicum in rodent or primate hosts. These antigens are unusually diverse in their structure and stage specificity. Interestingly, although all of the vaccine molecules characterized are situated in the tegument, their exposure on the parasite surface, in most instances, is transient and/or non-essential. The properties of four of these immunogens, glutathione-S-transferase (P26,28), paramyosin (Sm97), GP38, and GP18 are discussed. Despite the identification and recombinant synthesis of several promising protective antigens, vaccination of humans against schistosomiasis remains in the realm of fantasy. At the technical level, a major problem is the failure of any of the current vaccine immunogens and immunization protocols to induce levels of resistance sufficient for significant reduction of human infection or disease. Once this important hurdle is passed, human immunization trials should be attempted as the potential beneficial impact of a vaccine against schistosomiasis remains enormous.

Induction of protective immunity against Schistosoma mansoni by vaccination with schistosome paramyosin (Sm97), a nonsurface parasite antigen

Paramyosin (Sm97), a 97-kDa myofibrillar protein identified by the unusually monospecific antibody response induced by intradermal vaccination of mice with a complex soluble worm antigen preparation (SWAP) of adult Schistosoma mansoni administered with bacillus Calmette-Guérin (BCG), was purified and tested for its capacity to protect mice against challenge infection. When administered intradermally with BCG at total doses of only 4-40 micrograms per mouse, both the native molecule and a recombinant expression product containing approximately 50% of the whole protein were found to confer significant resistance (26-33%) against challenge infection, while 2 mg of unfractionated SWAP was required to induce similar levels of protection. In addition, paramyosin was shown to stimulate T lymphocytes from vaccinated mice to produce lymphokines [e.g., gamma interferon (IFN-gamma)] that activate macrophages to kill schistosomula. Neither schistosome myosin nor a heterologous paramyosin from a different invertebrate genus were protective, indicating a requirement for specific epitopes in the immunization. That the protection induced by paramyosin involves a T-cell-mediated mechanism was supported by the failure of anti-paramyosin antibodies to passively transfer significant resistance to infection to recipient mice. Lymphocytes from mice vaccinated with paramyosin were found to produce IFN-gamma in response to living schistosomula, suggesting that during challenge infection of vaccinated hosts, paramyosin (a nonsurface antigen) may elicit a protective T-cell response as a consequence of its release from migrating parasite larvae. Paramyosin-depleted SWAP was also found to be protective as well as stimulatory for T lymphocytes from SWAP-vaccinated mice, indicating that other antigens in this preparation may have immunoprophylactic potential. In summary, these results (i) suggest that the induction of T-cell-dependent cell-mediated immunity against soluble nonsurface antigens may be an effective strategy for immunization against multicellular parasites and (ii) in the case of schistosomes, identify paramyosin as a candidate vaccine immunogen in this category.

Evasion of the alternative complement pathway by metacyclic trypomastigotes of Trypanosoma cruzi: dependence on the developmentally regulated synthesis of surface protein and N-linked carbohydrate

Epimastigotes (EPI) of Trypanosoma cruzi are highly sensitive to lysis in fresh normal human serum by the alternative complement pathway (ACP). In contrast, metacyclic trypomastigotes (CMT) derived from EPI in stationary culture fail to activate the ACP and are thus resistant to serum-mediated lysis. To investigate the nature of the parasitic surface molecules which enable infective metacyclic trypomastigotes to evade the ACP, CMT were treated with a variety of different proteolytic and glycosidic enzymes, and their sensitivity to ACP-dependent lysis was tested. Pretreatment with pronase was found to cause a near complete reversal in the resistance of CMT to serum lysis, whereas trypsin or chymotrypsin induced smaller increases in complement sensitivity. Similarly, pretreatment with N-glycanase or neuraminidase also partially abrogated the resistance of CMT to ACP-dependent lysis. The effect of these enzymes on susceptibility to complement-mediated lysis was paralleled in increased C3 and C9 deposition on the organism. In addition, electrophoretic analysis of parasite-bound C3 indicated that the hemolytically inactive fragment, iC3b, was the major form of the molecule on CMT, while the hemolytically active fragment, C3b, predominated on pronase-treated CMT. Furthermore, when C3 was deposited on the parasite surface by means of purified ACP components, 80% of C3b on pronase-pretreated CMT but only 14% of the C3b on CMT bound the amplification protein factor B with high affinity, a prerequisite for efficient ACP activation. When cultured at 37 degrees C after pronase treatment, CMT gradually regained their resistance to ACP-mediated lysis. This process was blocked if puromycin, cycloheximide, or tunicamycin were included in the culture medium. The above findings suggest that evasion of the ACP by CMT is dependent on the developmentally regulated synthesis of protein as well as N-linked carbohydrate chains. A stage-specific 90,000 to 115,000 m.w. glycoprotein doublet present on the surface of CMT was shown to be uniquely sensitive to pronase digestion. Thus, this complex, which is also recognized by a CMT-specific monoclonal antibody, may be the glycoprotein component responsible for control of ACP activation

Evasion of the alternative complement pathway by metacyclic trypomastigotes of Trypanosoma cruzi: dependence on the developmentally regulated synthesis of surface protein and N-linked carbohydrate

Epimastigotes (EPI) of Trypanosoma cruzi are highly sensitive to lysis in fresh normal human serum by the alternative complement pathway (ACP). In contrast, metacyclic trypomastigotes (CMT) derived from EPI in stationary culture fail to activate the ACP and are thus resistant to serum-mediated lysis. To investigate the nature of the parasitic surface molecules which enable infective metacyclic trypomastigotes to evade the ACP, CMT were treated with a variety of different proteolytic and glycosidic enzymes, and their sensitivity to ACP-dependent lysis was tested. Pretreatment with pronase was found to cause a near complete reversal in the resistance of CMT to serum lysis, whereas trypsin or chymotrypsin induced smaller increases in complement sensitivity. Similarly, pretreatment with N-glycanase or neuraminidase also partially abrogated the resistance of CMT to ACP-dependent lysis. The effect of these enzymes on susceptibility to complement-mediated lysis was paralleled in increased C3 and C9 deposition on the organism. In addition, electrophoretic analysis of parasite-bound C3 indicated that the hemolytically inactive fragment, iC3b, was the major form of the molecule on CMT, while the hemolytically active fragment, C3b, predominated on pronase-treated CMT. Furthermore, when C3 was deposited on the parasite surface by means of purified ACP components, 80% of C3b on pronase-pretreated CMT but only 14% of the C3b on CMT bound the amplification protein factor B with high affinity, a prerequisite for efficient ACP activation. When cultured at 37 degrees C after pronase treatment, CMT gradually regained their resistance to ACP-mediated lysis. This process was blocked if puromycin, cycloheximide, or tunicamycin were included in the culture medium. The above findings suggest that evasion of the ACP by CMT is dependent on the developmentally regulated synthesis of protein as well as N-linked carbohydrate chains. A stage-specific 90,000 to 115,000 m.w. glycoprotein doublet present on the surface of CMT was shown to be uniquely sensitive to pronase digestion. Thus, this complex, which is also recognized by a CMT-specific monoclonal antibody, may be the glycoprotein component responsible for control of ACP activation

Induction of protective immunity against Schistosoma mansoni by a nonliving vaccine. IV. Fractionation and antigenic properties of a soluble adult worm immunoprophylactic activity

An aqueous buffer-soluble, nonparticulate fraction of adult Schistosoma mansoni worms (SWAP) was separated by gel filtration on Ultragel AcA-34, and portions of the eluate were tested for their capacity to induce protective immunity against cercarial challenge when administered intradermally to mice in combination with the adjuvant BCG. All of the immunogenic activity was found in a single peak of protein excluded in the void volume of the column. This same fraction was determined by SDS-PAGE and Western immunoblotting to be unique in that it contained a component of Mr (X 10(-3) 97 (97,000) recognized monospecifically by antibodies from mice vaccinated with unseparated SWAP plus BCG. Similarly, the protective fraction was unique in possessing the capacity to elicit 24 hr delayed footpad swelling responses, as well as lymphokine production, in SWAP-BCG-immunized mice. These results suggest that the immunogenic activity of SWAP resides in a restricted population of molecules, and possibly in the 97,000 antigen detected with antibodies from vaccinated animals. Because both the protective capacity of unfractionated SWAP and the serologic reactivity of the 97,000 antigen are sensitive to digestion with protease, it is likely that the immunologic activity of these molecules is dependent on peptide-bonded structural elements.

Induction of protective immunity against Schistosoma mansoni by a nonliving vaccine. IV. Fractionation and antigenic properties of a soluble adult worm immunoprophylactic activity

An aqueous buffer-soluble, nonparticulate fraction of adult Schistosoma mansoni worms (SWAP) was separated by gel filtration on Ultragel AcA-34, and portions of the eluate were tested for their capacity to induce protective immunity against cercarial challenge when administered intradermally to mice in combination with the adjuvant BCG. All of the immunogenic activity was found in a single peak of protein excluded in the void volume of the column. This same fraction was determined by SDS-PAGE and Western immunoblotting to be unique in that it contained a component of Mr (X 10(-3) 97 (97,000) recognized monospecifically by antibodies from mice vaccinated with unseparated SWAP plus BCG. Similarly, the protective fraction was unique in possessing the capacity to elicit 24 hr delayed footpad swelling responses, as well as lymphokine production, in SWAP-BCG-immunized mice. These results suggest that the immunogenic activity of SWAP resides in a restricted population of molecules, and possibly in the 97,000 antigen detected with antibodies from vaccinated animals. Because both the protective capacity of unfractionated SWAP and the serologic reactivity of the 97,000 antigen are sensitive to digestion with protease, it is likely that the immunologic activity of these molecules is dependent on peptide-bonded structural elements.

Molecular mimicry of a carbohydrate epitope on a major surface glycoprotein of Trypanosoma cruzi by using anti-idiotypic antibodies

The use of anti-idiotypic antibodies (Ab2) to induce anti-microbial immunity might be particularly advantageous with respect to responses directed against carbohydrate determinants, because it may not be feasible to reproduce these epitopes by recombinant DNA technology. In the present studies, rabbit Ab2 were produced against a recurrent BALB/c idiotype defined by a monoclonal antibody (WIC 29.26) with specificity for a carbohydrate epitope of a major surface glycoprotein of Trypanosoma cruzi. The Ab2 induced specific antibodies in mice, rabbits, and guinea pigs, and reacted with parasite-induced anti-T. cruzi antibodies from mice and rabbits as well as humans. The behavior of this Ab2 is therefore consistent with that of the antigen itself, and suggests that molecular mimicry of carbohydrate epitopes can be easily achieved.

Identification of cell surface carbohydrate and antigenic changes between noninfective and infective developmental stages of Leishmania major promastigotes

Differentiation of Leishmania major promastigotes from a noninfective to an infective stage has been demonstrated for promastigotes growing within axenic culture and within the sandfly vector. We have been attempting to identify specific biochemical or antigenic changes that are associated with the development of infective-stage promastigotes. In this report we demonstrate that during growth, cultured L. major promastigotes undergo selective changes in surface carbohydrates, determined by their agglutination by plant lectins. Thus, although all promastigotes from logarithmic (log)-phase cultures were agglutinated by the two-D-galactose-binding lectins, peanut agglutinin (PNA) and Ricinus communis, identical concentrations of these lectins failed to agglutinate approximately 50% of L. major promastigotes from the stationary-phase cultures. These changes in lectin-agglutinating properties are consistent with the fact that log-phase promastigotes represent a homogeneous population of noninfective parasites, whereas up to 50% of the stationary-phase organisms appear to be transformed into infective-stage promastigotes, as determined by their ability to survive within normal resident mouse peritoneal macrophages in vitro. The identities of the populations defined by infectivity and PNA agglutination were confirmed by the purification of PNA-unagglutinated promastigotes from stationary-phase cultures, which demonstrated that 100% of these promastigotes were able to establish intracellular infections. Lectin-purified, infective-stage promastigotes from the stationary phase were compared with noninfective promastigotes from the log phase for the purpose of identifying stage-specific antigens. On the basis of Western blot analysis and the immunoprecipitation of surface-labeled organisms, we have identified an antigen of roughly 116,000 Mr that is expressed on the surface of infective but not noninfective promastigotes.

Identification of cell surface carbohydrate and antigenic changes between noninfective and infective developmental stages of Leishmania major promastigotes

Differentiation of Leishmania major promastigotes from a noninfective to an infective stage has been demonstrated for promastigotes growing within axenic culture and within the sandfly vector. We have been attempting to identify specific biochemical or antigenic changes that are associated with the development of infective-stage promastigotes. In this report we demonstrate that during growth, cultured L. major promastigotes undergo selective changes in surface carbohydrates, determined by their agglutination by plant lectins. Thus, although all promastigotes from logarithmic (log)-phase cultures were agglutinated by the two-D-galactose-binding lectins, peanut agglutinin (PNA) and Ricinus communis, identical concentrations of these lectins failed to agglutinate approximately 50% of L. major promastigotes from the stationary-phase cultures. These changes in lectin-agglutinating properties are consistent with the fact that log-phase promastigotes represent a homogeneous population of noninfective parasites, whereas up to 50% of the stationary-phase organisms appear to be transformed into infective-stage promastigotes, as determined by their ability to survive within normal resident mouse peritoneal macrophages in vitro. The identities of the populations defined by infectivity and PNA agglutination were confirmed by the purification of PNA-unagglutinated promastigotes from stationary-phase cultures, which demonstrated that 100% of these promastigotes were able to establish intracellular infections. Lectin-purified, infective-stage promastigotes from the stationary phase were compared with noninfective promastigotes from the log phase for the purpose of identifying stage-specific antigens. On the basis of Western blot analysis and the immunoprecipitation of surface-labeled organisms, we have identified an antigen of roughly 116,000 Mr that is expressed on the surface of infective but not noninfective promastigotes.

Immunopathology of Schistosoma japonicum and S. mansoni infection in B cell depleted mice

To investigate the role of antibody in the pathogenesis of hepatic granulomas around schistosome eggs, mice were depleted of B cells by treatment from birth with anti-IgM serum and were subsequently infected with Schistosoma japonicum or S. mansoni. Anti-IgM treatment did not affect the development or fecundity of the worms or the larvae within the egg shells. Normal circumoval granulomas were present in the livers of B cell depleted mice 7 or 8 weeks after infection clearly indicating that antibody and immune complexes have no necessary role in the formation of granulomas. Hepatic fibrosis was also similar in B cell depleted and untreated mice at these times. Ten weeks after infection the size of S. japonicum egg granulomas in untreated mice had decreased but no change in the size of granulomas had occurred in B cell depleted mice, and hepatic fibrosis was more marked in treated than in untreated mice. Similar changes were noted in S. mansoni infected mice, assayed at 8 and at 12-13.5 weeks after infection. The effects of B cell depletion in the more chronic infections may be related to the absence of antibody but could also be caused by an influence on B cell-dependent suppressor T cells.

gp72, the 72 kilodalton glycoprotein, is the membrane acceptor site for C3 on Trypanosoma cruzi epimastigotes

We examined the interaction of complement component C3 with surface molecules on Trypanosoma cruzi. Five- to six-fold more C3 was bound to epimastigotes (Epi) than to metacyclic trypomastigotes (CMT) of strain M88. Epi and CMT were surface iodinated, then incubated in C8-deficient serum, and detergent lysates were applied to anti-C3 antibody that had been coupled to Sepharose. We found that 9.20-10.24% of applied 125I-Epi protein bound to anti-C3-sepharose, compared to 2.64% binding of 125I-CMT protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that C3 was attached to 125I-Epi protein by a covalent bond. Samples eluted from anti-C3-sepharose with hydroxylamine revealed a single, major, 72 kD band, suggesting that C3b attaches almost exclusively to the 72 kD glycoprotein of Epi by a hydroxylamine-susceptible ester bond. An antiserum was prepared from lysates of serum-treated Epi that had been affinity-purified on anti-C3-sepharose. This antiserum immunoprecipitated a single 72 kD component (gp72) from surface-iodinated Epi, and specifically recognized only gp72 from Epi in immunoblots. In contrast to the results with Epi, gp72 on CMT was not found to be an efficient acceptor molecule for C3 deposition. The results are the first to evaluate the acceptor site for C3 deposition on a parasite, and they show that gp72 on Epi, but not gp72 on CMT, serves as the preferential acceptor for C3 during antibody-independent alternative complement pathway activation.

Evidence against the existence of specific Schistosoma mansoni subpopulations which are resistant to irradiated vaccine-induced immunity

When mice are immunized with irradiated Schistosoma mansoni cercariae a proportion of the subsequent cercarial challenge always escapes killing and matures to egg-laying adults. This report investigates the possibility that incomplete immunity in this system is governed by a genetically-determined insusceptibility of a particular schistosome subpopulation. To do this we tested whether more immunoresistant schistosomes would develop following successive passages of progeny of the resistant worms through immunized mice. Mice were immunized with 500 50 Krad-irradiated cercariae, and challenged with normal cercariae when immunity was at its peak. After five successive passages through snails and immune mice, progeny of those parasites which escaped immune killing were no more refractory to vaccine-induced resistance than the original stock maintained in nonimmune mice. Additionally, the "passaged" isolates did not differ from the original stock in their ability to induce protection following irradiation. Our results indicate that with this model of acquired resistance incomplete immunity is unlikely to be due to a subpopulation of the parasites possessing a genetically-determined insusceptibility to killing.

Cryptic epitope explains the failure of a monoclonal antibody to bind to certain isolates of Trypanosoma cruzi

A mouse monoclonal antibody, WIC 29.26 Ab, has previously been characterized as recognizing a carbohydrate epitope on a 72,000 m.w. glycoprotein (GP72) expressed on the surface of Trypanosoma cruzi epimastigotes and metacyclic trypomastigotes. This molecule has been implicated as a receptor in the control of parasite transformation, and when used as an immunogen in mice, partially protects against T. cruzi infection. In previous experiments in which a radioimmunoassay was used, WIC 29.26 Ab was found to react with approximately 50% of T. cruzi strains and clones derived from a variety of sources. In this study, we attempted to determine whether the WIC 29.26 Ab-nonreactive isolates lack the entire GP72 or merely lack the epitope recognized by this monoclonal antibody. WIC 226.4 Ab, a monoclonal antibody raised against periodate-treated GP72, reacted in an immunofluorescence assay with all strains and clones studied, including those which had not reacted with WIC 29.26 Ab. Likewise, two polyvalent rabbit sera, directed specifically against GP72, bound to all T. cruzi isolates tested. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of detergent lysates of surface-labeled epimastigotes immunoprecipitated with WIC 29.26 Ab showed that the epitope bound by this antibody was present in all but one of the parasites that were surface-nonreactive, as well as in all those that were surface-reactive. WIC 29.26 Ab precipitated a single 72K Mr band from most strains and clones, but in several cases 79K Mr and 66K Mr bands were seen. Isolates from both the surface-reactive and the surface-nonreactive groups showed the latter pattern. These results demonstrate that GP72, or similar electrophoretic variants--and with one exception, the carbohydrate epitope bound by WIC 29.26 Ab--are present in the surface membrane of all strains and clones tested. This observation suggests that in intact epimastigotes of the surface-nonreactive isolates, the epitope is not accessible because of structural changes in the molecule itself or because of differences in the membrane environment of GP72.

Cryptic epitope explains the failure of a monoclonal antibody to bind to certain isolates of Trypanosoma cruzi

A mouse monoclonal antibody, WIC 29.26 Ab, has previously been characterized as recognizing a carbohydrate epitope on a 72,000 m.w. glycoprotein (GP72) expressed on the surface of Trypanosoma cruzi epimastigotes and metacyclic trypomastigotes. This molecule has been implicated as a receptor in the control of parasite transformation, and when used as an immunogen in mice, partially protects against T. cruzi infection. In previous experiments in which a radioimmunoassay was used, WIC 29.26 Ab was found to react with approximately 50% of T. cruzi strains and clones derived from a variety of sources. In this study, we attempted to determine whether the WIC 29.26 Ab-nonreactive isolates lack the entire GP72 or merely lack the epitope recognized by this monoclonal antibody. WIC 226.4 Ab, a monoclonal antibody raised against periodate-treated GP72, reacted in an immunofluorescence assay with all strains and clones studied, including those which had not reacted with WIC 29.26 Ab. Likewise, two polyvalent rabbit sera, directed specifically against GP72, bound to all T. cruzi isolates tested. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of detergent lysates of surface-labeled epimastigotes immunoprecipitated with WIC 29.26 Ab showed that the epitope bound by this antibody was present in all but one of the parasites that were surface-nonreactive, as well as in all those that were surface-reactive. WIC 29.26 Ab precipitated a single 72K Mr band from most strains and clones, but in several cases 79K Mr and 66K Mr bands were seen. Isolates from both the surface-reactive and the surface-nonreactive groups showed the latter pattern. These results demonstrate that GP72, or similar electrophoretic variants--and with one exception, the carbohydrate epitope bound by WIC 29.26 Ab--are present in the surface membrane of all strains and clones tested. This observation suggests that in intact epimastigotes of the surface-nonreactive isolates, the epitope is not accessible because of structural changes in the molecule itself or because of differences in the membrane environment of GP72.

Mechanisms of protective immunity against S. mansoni infection in mice vaccinated with irradiated cercariae. VI. Influence of the major histocompatibility complex

Inbred mouse strains develop different levels of resistance to challenge infection with Schistosoma mansoni in response to vaccination with irradiated cercariae. The role of the major histocompatibility complex (MHC) in determining this genetic polymorphism in acquired resistance was investigated. Previous studies suggested that inbred mice bearing either the b or d MHC haplotypes develop a higher level of vaccine induced resistance than do mice with other MHC haplotypes. An analysis of an F1 cross between an H-2b strain (C57BL/6) and an H-2k strain (C3H/HeJ) indicated that the ability to develop high levels of immunity is inherited in a dominant fashion. In order to confirm that the development of high resistance is an MHC associated trait, B10, C3H, BALB and B6 congenic mice bearing different H-2 haplotypes were compared. On either the B10, B6, or BALB background, substitution of b or d with k or a MHC alleles resulted in a decreased level of vaccine induced immunity. The observed decreases were more pronounced in BALB and B6 than in B10 congenics suggesting an influence of background (non-MHC linked) genes on protective immunity. Similarly, C3H.SW (H-2b) mice developed a significantly higher level of acquired resistance than C3H/HeSn (H-2k) mice. Cross and backcross experiments between H-2b and H-2k B6 congenic mice confirmed the dominant inheritance of high resistance as well as the MHC linkage of the trait. These data indicate that the MHC locus exerts a quantitative influence on vaccine induced resistance in certain inbred mouse strains and provide further support for the concept that the protection elicited by irradiated cercariae is the manifestation of a specific host immune response.

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. IV. Analysis of the role of IgE antibodies and mast cells

Mice resistant to challenge infection with Schistosoma mansoni by vaccination with highly irradiated cercariae were examined for the presence of circulating IgE antibodies and peritoneal mast cells sensitized against schistosome antigens. Significant levels of SWAP- or CAP-specific IgE antibodies could not be detected by solid phase radioimmunoassay in the sera of C57BL/6 mice during the first 6 wk after vaccination. Similarly, heatlabile antibodies capable of passively sensitizing normal mast cells for degranulation in response to SWAP could not be identified in the same sera. In contrast, peritoneal mast cells harvested from C57BL/6 mice 2 wk or later after vaccination gave strong degranulation responses when challenged with SWAP or CAP. Thus, vaccination with irradiated cercariae induces an unusual form of immediate-type hypersensitivity in which mast cells become sensitized in the absence of detectable circulating IgE antibodies. Mice deficient in mast cells (W/Wv mutant strain) were observed to develop the same resistance to challenge infection after vaccination with irradiated cercariae as nondeficient littermates. Similarly, vaccinated SJL/J mice were found to mount an extremely weak IgE response as measured by mast cell degranulation yet displayed the same level of resistance to challenge infection as other inbred mice developing potent mast cell responses. These findings argue that IgE antibodies and mast cells are not essential components in the effector mechanism of irradiated vaccine-induced immunity against schistosome infection.

Macrophages as effector cells of protective immunity in murine schistosomiasis. VI. T cell-dependent, lymphokine-mediated, activation of macrophages in response to Schistosoma mansoni antigens

Macrophages from Schistosoma mansoni-infected mice kill significant numbers of skin stage schistosomula and murine fibrosarcoma cells in vitro. In order to determine whether the macrophage tumoricidal and larvicidal activation observed in mice as a result of S. mansoni infection are mediated through T cell-dependent (lymphokine) or B cell-dependent (antibody or immune complex) mechanisms, the development of macrophage populations with cytotoxic activity against schistosome larvae or tumor cells was monitored in S. mansoni-infected nude or mu-suppressed mice. Whereas peritoneal cells from S. mansoni-infected congenitally athymic mice had no activity in either assay, cells from mu-suppressed S. mansoni-infected mice showed cytotoxic activity equivalent to that of cells from untreated S. mansoni-infected counterparts. Cells from mu-suppressed uninfected mice were not activated. The mu-suppressed animals had no detectable nonspecific IgM or specific antischistosome IgM, IgG, or IgE antibodies and showed a 90% reduction in numbers of splenic IgM+ cells upon fluorescence activated cell sorter analysis. These results indicate that antibody is not required for in vivo activation of macrophages during S. mansoni infection. Further experiments showed that lymphoid cells from S. mansoni infected mice respond in culture with various specific antigens (such as living or dead whole schistosomula or soluble adult worm antigens) by production of factors capable of activating macrophages from uninfected control mice to kill schistosomula or tumor cells in vitro. Macrophage-activating factors were produced by T cell-enriched, but not T cell-depleted or B cell-enriched, populations from spleens of schistosome-infected mice in response to schistosome antigen. Similar lymphokines may be responsible for the macrophage activation observed during chronic murine schistosomiasis. These observations emphasize the potential contribution of T cell-mediated immune mechanisms in resistance to S. mansoni infection.

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. IV. Analysis of the role of IgE antibodies and mast cells

Mice resistant to challenge infection with Schistosoma mansoni by vaccination with highly irradiated cercariae were examined for the presence of circulating IgE antibodies and peritoneal mast cells sensitized against schistosome antigens. Significant levels of SWAP- or CAP-specific IgE antibodies could not be detected by solid phase radioimmunoassay in the sera of C57BL/6 mice during the first 6 wk after vaccination. Similarly, heatlabile antibodies capable of passively sensitizing normal mast cells for degranulation in response to SWAP could not be identified in the same sera. In contrast, peritoneal mast cells harvested from C57BL/6 mice 2 wk or later after vaccination gave strong degranulation responses when challenged with SWAP or CAP. Thus, vaccination with irradiated cercariae induces an unusual form of immediate-type hypersensitivity in which mast cells become sensitized in the absence of detectable circulating IgE antibodies. Mice deficient in mast cells (W/Wv mutant strain) were observed to develop the same resistance to challenge infection after vaccination with irradiated cercariae as nondeficient littermates. Similarly, vaccinated SJL/J mice were found to mount an extremely weak IgE response as measured by mast cell degranulation yet displayed the same level of resistance to challenge infection as other inbred mice developing potent mast cell responses. These findings argue that IgE antibodies and mast cells are not essential components in the effector mechanism of irradiated vaccine-induced immunity against schistosome infection.

Macrophages as effector cells of protective immunity in murine schistosomiasis. VI. T cell-dependent, lymphokine-mediated, activation of macrophages in response to Schistosoma mansoni antigens

Macrophages from Schistosoma mansoni-infected mice kill significant numbers of skin stage schistosomula and murine fibrosarcoma cells in vitro. In order to determine whether the macrophage tumoricidal and larvicidal activation observed in mice as a result of S. mansoni infection are mediated through T cell-dependent (lymphokine) or B cell-dependent (antibody or immune complex) mechanisms, the development of macrophage populations with cytotoxic activity against schistosome larvae or tumor cells was monitored in S. mansoni-infected nude or mu-suppressed mice. Whereas peritoneal cells from S. mansoni-infected congenitally athymic mice had no activity in either assay, cells from mu-suppressed S. mansoni-infected mice showed cytotoxic activity equivalent to that of cells from untreated S. mansoni-infected counterparts. Cells from mu-suppressed uninfected mice were not activated. The mu-suppressed animals had no detectable nonspecific IgM or specific antischistosome IgM, IgG, or IgE antibodies and showed a 90% reduction in numbers of splenic IgM+ cells upon fluorescence activated cell sorter analysis. These results indicate that antibody is not required for in vivo activation of macrophages during S. mansoni infection. Further experiments showed that lymphoid cells from S. mansoni infected mice respond in culture with various specific antigens (such as living or dead whole schistosomula or soluble adult worm antigens) by production of factors capable of activating macrophages from uninfected control mice to kill schistosomula or tumor cells in vitro. Macrophage-activating factors were produced by T cell-enriched, but not T cell-depleted or B cell-enriched, populations from spleens of schistosome-infected mice in response to schistosome antigen. Similar lymphokines may be responsible for the macrophage activation observed during chronic murine schistosomiasis. These observations emphasize the potential contribution of T cell-mediated immune mechanisms in resistance to S. mansoni infection.

Lack of resistance to Schistosoma japonicum in mice immunized with irradiated S. mansoni cercariae

Mice immunized with irradiated Schistosoma mansoni cercariae were resistant to challenge with S. mansoni cercariae (mean resistance 53%) but not to challenge with S. japonicum cercariae (mean resistance -5%). Furthermore, the antibodies induced by vaccination with irradiated S. mansoni cercariae were more reactive with S. mansoni than with S. japonicum schistosomula. These results support the concept that the resistance induced by vaccination with irradiated cercariae is immunologically specific.

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. II. Analysis of immunity in hosts deficient in T lymphocytes, B lymphocytes, or complement

Laboratory mice with genetic or induced immunodeficiencies were vaccinated with irradiated cercariae of Schistosoma mansoni and assayed 4 wk later for their resistance to challenge infection. Athymic nude mice failed to develop immunity to challenge or detectable antibody responses to schistosomula, whereas heterozygote (nu/+) controls and nude mice with thymus grafts displayed highly significant levels of resistance and anti-schistosomulum antibody. Similarly, no resistance or antibody production as observed in vaccinated mice that had been made deficient in B lymphocytes by the injection of anti-mu-chain antisera from birth. In contrast, normal levels of vaccine-induced resistance were observed in mice genetically deficient in the fifth component of complement (C5) and in mice decomplemented before challenge by treatment with cobra venom factor. These results indicate that the resistance to challenge infection induced by irradiated cercariae is both thymus and B lymphocyte dependent and therefore is likely to result from specific immune responses directed against schistosome worms. The data also argue against a role for complement in the effector mechanism of vaccine-induced immunity.

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. II. Analysis of immunity in hosts deficient in T lymphocytes, B lymphocytes, or complement

Laboratory mice with genetic or induced immunodeficiencies were vaccinated with irradiated cercariae of Schistosoma mansoni and assayed 4 wk later for their resistance to challenge infection. Athymic nude mice failed to develop immunity to challenge or detectable antibody responses to schistosomula, whereas heterozygote (nu/+) controls and nude mice with thymus grafts displayed highly significant levels of resistance and anti-schistosomulum antibody. Similarly, no resistance or antibody production as observed in vaccinated mice that had been made deficient in B lymphocytes by the injection of anti-mu-chain antisera from birth. In contrast, normal levels of vaccine-induced resistance were observed in mice genetically deficient in the fifth component of complement (C5) and in mice decomplemented before challenge by treatment with cobra venom factor. These results indicate that the resistance to challenge infection induced by irradiated cercariae is both thymus and B lymphocyte dependent and therefore is likely to result from specific immune responses directed against schistosome worms. The data also argue against a role for complement in the effector mechanism of vaccine-induced immunity.