Induction of protective immunity against Schistosoma mansoni by a nonliving vaccine. III. Correlation of resistance with induction of activated larvacidal macrophages

Mice protected against Schistosoma mansoni infection by intradermal (i.d.) immunization with nonliving larval or adult worm antigens plus bacterial adjuvant developed 24-hr skin test responsiveness to schistosome antigens with the histologic features of delayed hypersensitivity. Intraperitoneal antigen injection elicited a mononuclear cell-enriched exudative population containing macrophages activated for direct cytotoxicity against schistosomula and tumor cell targets. This was likely to be due to in vivo exposure to macrophage-activating lymphokines, since these cells were unresponsive to further lymphokine stimulation in vitro and splenocytes from immunized mice reacted to specific in vitro antigen challenge by production of lymphokines capable of conferring larvacidal activity upon control macrophages. In contrast, mice treated with schistosome antigens by i.v. injection, which were not protected against challenge infection, failed to develop delayed hypersensitivity or activated macrophages in response to specific antigen challenge in vivo, and the titers of macrophage-activating lymphokine produced by in vitro antigen-stimulated splenocytes from these mice were threefold to fourfold lower than those produced by cells from animals immunized by the i.d. route. Thus, sensitization for cell-mediated immune responses including lymphokine production and macrophage activation correlated with induction of resistance to S. mansoni in this model of vaccination.     

Defective vaccine-induced resistance to Schistosoma mansoni in P strain mice. III. Specificity of the associated defect in cell-mediated immunity

In contrast to many other strains, inbred P strain mice fail to develop significant levels of resistance to challenge Schistosoma mansoni infection as a result of prior vaccination with radiation-attenuated cercariae. In this study, the relationship between defects in resistance and development of cell-mediated immune reactivity was examined. Although splenocytes from immunized P mice demonstrated deficiencies in production of macrophage-activating lymphokine(s) in response to either antigenic or mitogenic stimulation, other aspects of T lymphocyte responsiveness including blastogenesis, production of interleukin 2, interleukin 3 and macrophage chemotactic factor, as well as helper cell function for secondary plaque-forming cell response to a T-dependent antigen and allospecific cytolytic T cell reactivity, appeared to be comparable with those of C57BL/6 mice, a strain that is protected by vaccination against S. mansoni. FACS comparison revealed no significant deficits in percentages of Thy-1+, Lyt-1+, or L3T4+ splenocytes in vaccinated P mice. The P-associated defect in production of macrophage-activating factor appeared to be at the level of the T cell rather than the antigen-presenting cell, because macrophages from P mice could reconstitute the lymphokine-producing capacity of T-enriched splenocytes from immunized, resistant (C57BL/6 X P) F1 or B10.P mice, whereas the converse was not true. These results indicate that vaccinated P mice have a selective defect in T cell function for production of macrophage-activating lymphokine, which is manifested as a failure to produce activated larvicidal macrophages at the site of specific antigen challenge in vivo and may be associated with the failure of this strain to become resistant to S. mansoni.     

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.     

Induction of protective immunity against Schistosoma mansoni by a nonliving vaccine is dependent on the method of antigen presentation

A preparation of nonliving parasite antigens containing both soluble and particulate components of frozen-and-thawed invasive larvae was used to immunize C57BL/6J mice against challenge Schistosoma mansoni infection. The method of antigen presentation was observed to be critical to the ability of this preparation to induce protective immunity, because intradermal administration in conjunction with a bacterial adjuvant (BCG) resulted in strong protection against challenge parasites (51% reduction in worm burden in six experiments), whereas i.v. injection of the same antigenic preparation was completely ineffective. Induction of resistance was accompanied by specific immune responsiveness toward schistosome antigens. Protection correlated more closely with sensitization for specific delayed hypersensitivity than with elicitation of circulating antibodies to larval surface antigens or immediate hypersensitivity in these models. These results suggest that it will be possible to design a defined vaccine against S. mansoni infection, but that identification of the route of antigen presentation that most effectively elicits relevant immune effector mechanisms will be crucial to the success of any vaccination protocol involving nonliving antigens.     

Induction of protective immunity against Schistosoma mansoni by a non living vaccine. I. Partial characterization of antigens recognized by antibodies from mice immunized with soluble schistosome extracts

A single intradermal injection of frozen and thawed schistosomula in conjunction with the bacterial adjuvant Mycobacterium bovis strain Bacille Calmette Guerin, Phipps substrain (BCG) induced significant levels of resistance to challenge Schistosoma mansoni infection in C57BL/6 mice. Immunization with the aqueous fraction remaining after 100,000 X G centrifugation of the larval lysate was also protective under these conditions, suggesting that some immunogenic determinants may not be membrane associated. Frozen-thawed cercariae and soluble components of adult worms also protected against challenge infection in these experiments. These observations indicate that soluble immunogens are present in both early and late developmental stages of the parasite, and therefore may be good candidate antigens for an immunochemically defined vaccine against schistosomiasis. Induction of humoral reactivity against soluble or membrane antigens was examined in mice protected against cercarial challenge by prior exposure to frozen-thawed larvae, soluble larval, or soluble adult antigens plus BCG. Animals that were immunized with frozen-thawed larvae produced low but significant levels of antibodies against larval surface antigens when examined by indirect immunofluorescence or by immunoprecipitation of surface-labeled schistosomula. Mice immunized with soluble antigens, however, showed negligible antibody reactivity against surface membrane antigens. Because mice immunized with soluble antigens were resistant to challenge infection, these results strongly suggest that anti-surface membrane reactivity is not required in the mechanism of protective immunity in this model. Sera from mice immunized with either total freeze-thaw larval lysate or soluble schistosome extracts all showed strong reactivity against soluble antigens, as detected by ELISA. Western blot analysis showed these antisera to react with a restricted number of high m.w. antigens that were present both in schistosomula and in adult worms. These antigens are therefore likely to play a major role in the development of resistance in this model as immunogens and/or as targets of protective immune response.     

Defective vaccine-induced immunity to Schistosoma mansoni in P strain mice. I. Analysis of antibody responses

Inbred P4 strain mice have previously been shown to be uniquely defective in their resistance to challenge infection induced by irradiated cercariae of Schistosoma mansoni. To assess whether the low levels of resistance developed by vaccinated P mice could be due to a defective antibody response, we compared the anti-schistosomulum antibody responses in vaccinated P animals with those occurring in vaccinated C57BL/6J (B6) mice, a strain that consistently develops high levels of resistance to challenge infection. Our results indicate that vaccinated P mice develop levels of total anti-schistosomulum antibodies that are significantly lower than those occurring in B6 mice for at least 15 wk after immunization, with the exception of the fifth week, at which time the responses are indistinguishable. Further analysis revealed that the defect in P strain antibody response occurs specifically in the IgM isotype and that specific IgM levels in P mice are less than one-half the levels in B6 mice at every time point examined. In contrast, no differences in total IgM immunoglobulins were evident when sera from normal (nonvaccinated) P and B6 mice were compared. P mouse anti-schistosomulum IgG antibody responses reached the same levels as those observed in B6 mice by 5 wk after vaccination. However, a much faster decay in IgG antibody levels occurred after this time point in P animals. No differences were observed when the levels of anti-schistosomulum antibodies occurring in each of the major IgG isotypes (IgG1, IgG2a, IgG2b, IgG3) were compared in sera from P and B6 mice vaccinated 4 wk previously. Similarly, vaccinated P and B6 mice were found to mount indistinguishable IgG anamnestic responses after challenge infection. Finally, no differences between vaccinated P and B6 mice were observed when immediate (30 min) skin test and mast cell degranulation responses to a soluble schistosome antigenic preparation were compared. The above findings suggest that P strain mice have a specific defect in their ability to mount IgM antibody responses after immunization with irradiated cercariae. The possible contribution of this defect in IgM response to the decreased resistance of vaccinated P mice to challenge infection is discussed.     

Influence of interleukin-2 and interferon-gamma in murine schistosomiasis

Schistosoma mansoni-infected mice were administered at the time of parasite residency in the lung with recombinant murine interleukin (IL)-2 or interferon-gamma (IFN-gamma), to evaluate the impact of cytokines in host responses to primary schistosomiasis. S. mansoni lung-stage schistosomula did not affect plasma lipids levels in BALB/c, while elicited significant (p<0.05) increase in free fatty acids (FA) and decrease in cholesterol plasma levels in C57BL/6 and CD1 mice, and stimulated expression of mRNA for Th2 cytokines in BALB/c and Th1 cytokines in C57BL/6 and CD1 mice. Production of specific antibodies was negligible in the 3 strains. Interleukin-2 treatment elicited significant (p<0.001) decrease in triglycerides (TG) in CD1, and decrease in TG and cholesterol plasma levels and down-regulation of TNF-alpha mRNA expression in C57BL/6 mice. Induction of type 2 cytokines and/or IFN-gamma mRNA expression did not lead to increase in percentage of specific antibody responders in any mouse strain. Exogenous IL-2-related reduction in cholesterol plasma levels and TNF-alpha mRNA expression in C57BL/6 mice was associated with significant (p<0.05) decrease in adult worm recovery and egg count. Treatment with IFN-gamma elicited significant (p<0.05) free FA plasma levels increase in BALB/c and C57BL/6 and decrease in CD1 mice. Expression of type 2 cytokines mRNA was stimulated in BALB/c and CD1 mice, yet was not accompanied with increase in humoral responses. Exogenous IFN-gamma-related reduction in free FA plasma levels and IFN-gamma mRNA response, and up-regulation of TNF-alpha mRNA expression in CD1 mice were associated with significant increase in adult worm burden and egg load. The data were discussed in an attempt to define host factors predictive of resistance to schistosome infection.     

Induction of protective immunity against Schistosoma mansoni by a nonliving vaccine. II. Response of mouse strains with selective immune defects

The efficacy of a new vaccination procedure against Schistosoma mansoni, involving intradermal injection of nonliving antigen combined with the bacterial adjuvant Mycobacterium bovis strain bacillus Calmette Guérin, was tested in several strains of mice. Development of protection against subsequent infection was compared with in vivo skin test reactivity and in vitro humoral reactivity to soluble and surface-associated schistosome antigens. Significant levels of resistance and immune response were displayed by many inbred mouse strains, including C57BL/6J, C3H/HeN, and CBA/J, as well as outbred Swiss-Webster mice. However, no definite correlation was observed between the level of any particular immune response and the level of resistance to challenge S. mansoni infection. Development of protective immunity was also examined in mice with various immune defects, to determine whether these responses are relevant to resistance in this model. Animals with defective specific immediate hypersensitivity response due to deficiencies in IgE (SJL/J) or mast cell (W/Wv) production displayed strong resistance as a result of immunization. Likewise, mice bearing the lpsd (C3H/HeJ) or xid (CBA/N) mutations, affecting cellular or humoral response to certain thymus-independent antigens, developed significant levels of resistance after immunization. A/J mice, with defects in cellular recognition of bacterial endotoxin as well as deficiencies in natural killer cell activity and complement function, also showed significant protective immunity. Thus, these reactivities do not appear to be essential to the resistance against S. mansoni induced by the nonliving vaccine. Two nonresponder strains were identified, P and BALB/c. P mice were defective in specific delayed hypersensitivity response as well as resistance to infection. However, BALB/c mice showed no obvious immune deficiencies at the time of challenge. These results agreed with previous findings in mice immunized by exposure to radiation-attenuated cercariae with one exception; BALB/c mice were protected by vaccination with irradiated cercariae but not by the nonliving vaccine. Thus, further examination of immune response in mice identified in this study as high and low responder strains should allow characterization of critical immune resistance mechanisms induced by the nonliving vaccine, as well as immune mechanisms operating in common between these two models of resistance to S. mansoni.     

Comparison of the protective resistance induced by 60Co-irradiated cercariae and schistosomula of the WFFS and NMRI strains of Schistosoma mansoni

Mice, CBA/HT6T6 and C57BL/10, were vaccinated with 1 X 350 or 1 X 500 Schistosoma mansoni cercariae or schistosomula attenuated with 20 or 56 krad 60Co irradiation and challenged with 200 cercariae. Protective resistance against homologous strain challenge was compared using the Winches Farm Field Station (WFFS) and Naval Medical Research Institute (NMRI) strains of S. mansoni. Maximal resistance to challenge was obtained in both strains of mice with cercariae or schistosomula of either WFFS or NMRI strain attenuated with 20 krad. Protection using organisms attenuated with 56 krad was significantly lower. Since previous studies with the two parasite strains have shown that the biological effects of irradiation are similar, the difference in the immunogenicity of the 56 krad-irradiated NMRI strain in this study from earlier studies must be due either to different local conditions for irradiation or to adaptation of the NMRI strain to a new laboratory environment. This finding may have important implications for vaccination studies and investigations of the mechanisms of immunity where radiation-attenuated parasites are used.     

Schistosoma mansoni polypeptides immunogenic in mice vaccinated with radiation-attenuated cercariae

We compared the humoral immune response of mice protected against Schistosoma mansoni by vaccination with radiation-attenuated cercariae to that of patently infected mice, and we identified antigens that elicit a greater, or unique, immune response in the vaccinated mice. These comparisons were based upon radioimmunoprecipitations and immunodepletion of [35S]methionine-labeled schistosomular and adult worm polypeptides, followed by one- and two-dimensional polyacrylamide gel analyses. The humoral responses of patently infected mice and of mice vaccinated once were remarkably similar and were directed against schistosome glycoproteins ranging in molecular size from greater than 300 to less than 10 kDa. Exposing mice to a second vaccination resulted in a marked change in the immune response, to one predominantly directed toward high molecular size glycoproteins. Sequential immunodepletion techniques identified five schistosomular and seven adult worm antigens that showed a greater or unique immunogenicity in vaccinated mice as compared with patently infected mice. These adult worm antigens were purified by preparative sequential immunoaffinity chromatography and used to prepare a polyclonal antiserum, anti-irradiated vaccine. This antiserum bound to the surface of live newly transformed and lung-stage schistosomula, as assessed by immunofluorescence assays, and was reactive with a number of 125I-labeled schistosomular surface polypeptides, including a doublet of 150 kDa that was also recognized by sera of vaccinated mice but not by sera of patently infected mice.     

Lung-phase immunity to Schistosoma mansoni. Flow cytometric analysis of macrophage activation states in vaccinated mice

A delayed-type hypersensitivity response has been postulated as the effector mechanism of lung-phase immunity to Schistosoma mansoni. We have sought evidence for this response by examining the state of alveolar macrophage activation in C57BL/6 mice vaccinated with radiation-attenuated cercariae, and challenged with normal parasites. As an index of activation, the capacity of macrophages to produce an oxidative burst upon stimulation with PMA, was measured at the single cell level by a flow cytometric method. Fourteen to 28 days after vaccination with 20-kr parasites, highly activated macrophages were recovered from the airways by bronchoalveolar lavage. Their probable role in resistance is to recruit T lymphocytes and macrophages to "arm" the lungs against subsequent challenge. The level of macrophage activation had declined to near background by the time challenge parasites arrived, although pulmonary leucocyte numbers remained elevated. Activated alveolar macrophages were not detected after vaccination with 80-kr parasites, which fail to reach the lungs or induce resistance. Challenge parasites, arriving in the lungs of 20-kr vaccinated mice, stimulated a rapid increase in the activation state of recruited macrophages, coincident with their retention in the pulmonary vasculature. These events occurred later in challenge control mice, with peak activation at day 21, when migration of parasites to the liver is complete. Mice vaccinated with 80-kr parasites lacked the accelerated response to challenge, behaving like the control group. The absence of activated peritoneal macrophages suggests a response restricted to organs such as the lungs, through which both vaccinating and challenge parasites migrate. We suggest that the role of activated alveolar macrophages in lung-phase immunity is to initiate and maintain the focal inflammatory responses which block onward migration of parasites and lead to their demise.     

Modulation of granulomatous hypersensitivity against Schistosoma mansoni eggs in mice vaccinated with culture-derived macrophages loaded with PIII

Granuloma modulation induced by antigen is an attractive model for vaccination studies of experimental schistosomiasis to test the effect of anti-pathology vaccine. We describe here an immunization procedure with culture derived macrophages-pulsed PIII, a known anionic antigen purified from S. mansoni adult worm, involved in the inhibition of granulomatous response to eggs. For our studies, peritoneal or spleen macrophages cultured over 15 days were loaded with PIII. Both macrophage sub-populations were capable to efficiently take up and subsequently present PIII to lymphocytes as evidenced by immunofluorescence assay. The vaccination of mice with intravenous injection of PIII-loaded macrophages potently induced antigen-specific immune response to S. mansoni antigens as determined by cell proliferation assay. This immunization procedure of mice caused significant decrease in hepatic granuloma formation and in vitro granuloma reaction to S. mansoni antigens coupled to polyacrylamide beads (PB-SEA, PB-SWAP or PB-PIII). Assessment of in vitro granuloma supernatant of spleen cells from PIII-loaded macrophages vaccinated mice revealed significant amounts of Th1-cytokines IFN-gamma and IL-2 compared to control cells. Collectively, our results indicate that culture derived-macrophages provided a valuable research tool to investigate aspects of immune response that promote modulation of granulomatous hypersensitivity to S. mansoni eggs in mice.     

A Schistosoma mansoni 62-kDa band is identified as an irradiated vaccine T-cell antigen and characterized as calreticulin

The Schistosoma mansoni soluble adult worm antigen (SAWA) bands of 62/60 kDa were found to contain immunodominant T-cell immunogen(s) in irradiated cercariae-immunized Swiss and C57BL/6 mice. In the present study, spleen T cells of BALB/c mice immunized twice with ultraviolet light-irradiated cercariae proliferated and produced interleukin 4 in response to the 62/60-kDa SAWA bands in T-cell western assays. To characterize the 62/60-kDa bands, an adult S. mansoni worm cDNA expression library constructed in lambdagt11 was immunoscreened with serum of mice immunized with the 62/60-kDa antigens, and the immunoreactive cDNA inserts were sequenced. Purified 62- and 60-kDa proteins were used for amino acid microsequencing and for immunization studies in Swiss, C57BL/6, and BALB/c mice and rabbits. Taken together, the data indicated that the 60-kDa molecules are poorly immunogenic in mice and rabbits, whereas the 62-kDa species identified as S. mansoni calreticulin, is a good T- and B-cell antigen and represents a potential vaccine candidate.     

T cell-derived cytokines associated with pulmonary immune mechanisms in mice vaccinated with irradiated cercariae of Schistosoma mansoni.

In C57Bl/6 strain mice vaccinated with attenuated cercariae of Schistosoma mansoni, the major site of immune elimination of normal challenge parasites is the lungs. The immune effector mechanism involves formation of focal inflammatory responses; the abundance of CD4+ T cells and the activation of alveolar macrophages suggests a role for inflammatory cytokines. We report the profile of cytokines produced by cultures of leukocytes recovered by bronchoalveolar lavage (BAL) from the lungs of vaccinated and challenged mice. From 14 days after vaccination, BAL cultures contained infiltrating lymphocytes that produced abundant quantities of IFN-gamma and IL-3 on stimulation with larval Ag. Production declined from day 21 although the infiltrate of lymphocytes persisted. Challenge of vaccinated mice resulted in a second influx of IFN-gamma and IL-3-producing cells, earlier than after vaccination or in the appropriate controls. Ablation studies revealed that CD4+ T cells were essential for the production of IFN-gamma. The timing of cytokine production after vaccination, and challenge was coincident with the phases of macrophage activation previously reported. At no time could lymphocytes in BAL cultures be stimulated to proliferate with either larval Ag or mitogen, in contrast to splenocytes from the same mice. Furthermore, T cell growth factor activity was not detected in BAL cultures stimulated with Ag. We suggest that the lymphocytes recruited to the lungs are memory/effector cells. When Ag released from challenge schistosomula is presented to these cells, they respond by secreting cytokines that mediate the formation of cellular aggregates around the parasites, blocking their onward migration.     

In vivo T cell depletion regulates resistance and morbidity in murine schistosomiasis

These studies assessed the roles of subpopulations of T lymphocytes in inducing and modulating resistance to schistosomiasis and thereby influencing subsequent morbidity. C57BL/6 mice were depleted in vivo of Lyt-1+, Lyt-2+, and L3T4+ cells by the daily administration of monoclonal antibodies. The development of protective immunity, induced by exposure to irradiated Schistosoma mansoni cercariae as expressed in depleted animals, was compared to that demonstrated in undepleted, normal, and congenitally athymic C57BL/6 mice. The development of morbidity was determined by spleen weight, portal pressure and reticuloendothelial system activity. The results indicated that depletion of specific subpopulations of T lymphocytes minimally affected the primary development of parasites; however, depletion strongly influenced the development of resistance to the parasite and subsequent morbidity due to infection. Depletion of T lymphocytes by anti-Lyt-1+ or anti-L3T4+ antibody decreased the development of resistance, antibody and delayed-type hypersensitivity directed against schistosome antigens. Morbidity due to disease was increased. Depletion of Lyt-2+ cells produced opposite changes with augmented resistance and reduced morbidity. Congenitally athymic mice developed minimal resistance and morbidity. Moreover, resistance was inversely related to the morbidity shown by a given animal. These studies indicate that the development of protective immunity to S. mansoni cercariae is regulated by discrete subpopulations of T lymphocytes. The feasibility of decreasing morbidity by increasing specific immunologically mediated resistance is suggested.     

Vaccination against schistosomiasis in mice with killed schistosomula without adjuvant

Attempts to develop a killed vaccine against schistosomiasis have generally resulted in failure. There are two recent reports, but unfortunately, harsh adjuvants were used in conjunction with the antigenic materials. In our laboratory, a killed vaccine was developed by freezing (-196 degrees C) and thawing the schistosomula of S. mansoni. The use of such a preparation without adjuvant was effective in vaccinating mice. A worm reduction of 36.4-41.1% was achieved by one vaccinating injection, a 60.2% worm reduction by 3 injections, and a 63.7-66.0% reduction by 5 injections. The sequence of the development and the expression of the immune reactions were similar to those previously found in hosts immunized with highly X-irradiated schistosome organisms. Delayed hypersensitivity was demonstrated in histological sections of the skin in the challenged mice after one vaccination, showing that an adjuvant was not necessary to initiate the induction of cellular immunity.     

Variations in the response of five strains of mice to Leishmania mexicana.

Five strains of mice were studied in their ability to support Leishmania mexicana infection. Four strains, AKR, C57BL/6, DBA/2 and NMRI, were relatively resistant to cutaneous leishmaniasis. These strains developed delayed type hypersensitivity responses to leishmanial antigens and produced agglutinating antibodies. On the other hand Balb/c mice, highly susceptible to infection, failed to develop delayed type hypersensitivity responses and showed an impaired production of antibodies. Hybrids produced by mating C57BL/6 males and Balb/c females were no more susceptible than C57BL/6 mice, suggesting that resistance is inherited as a dominant character.     

Decreased binding of cytotoxic antibody by developing Schistosoma mansoni. Evidence for a surface change independent of host antigen adsorption and membrane turnover.

Schistosoma mansoni schistosomula maintained in chemically defined culture media became increasingly resistant to the cytotoxic effects of infected guinea pig serum. Two- and 6-day-old schistosomula recovered from mice showed no uptake of IgG antibody from infected guinea pig serum, as revealed by the indirect fluorescent antibody test. Results from this test remained negative when the schistosomula were tested at 0 C, after exposure to drugs which inhibit synthetic and secretory processes, or after being killed by heat or formalin. In contrast, new schistosomula collected within 3 hr after skin penetration bound IgG from infection serum under all test conditions, and showed increased susceptibility to cytotoxicity after exposure to various drugs. It thus appears that soon after skin penetration schistosomula undergo surface changes which prevent binding of antibody from infection serum. These changes can apparently take place in the absence of host antigens, and once they have occurred, do not depend on worm physiological processes for their function.     

Peptides and multiple antigen peptides from Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase: preparation, immunogenicity and immunoprotective capacity in C57BL/6 mice.

Four monoepitopic MAPs (MAP A, B, C and E) and one bis-diepitopic MAP B-E derived fromthe primary sequence of Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase, previously tested in BALB/c mice, were examined for their immunogenicity and protective capacity in C57BL/6 mice. Despite multimerization into MAPs, MAP Aand MAP C were poorly immunogenic. In contrast toBALB/c mice, MAP E was non-immunogenic in C57BL/6 mice. Peptide B in the form of MAP B orbis-diepitopic MAPB-E elicited immune responses in C57BL/6 mice that were associated with a significant decrease in worm burden. The MAPs were prepared by the stepwise solid-phase peptide synthesis using Boc/Bzl chemistry, successfully purified on the RP-HPLC column and characterized by RP-HPLC, HPCE and MALDI-TOF MS techniques. A general strategy for MAPs purification is discussed here and the purification of MAP Band MAP E is documented in detail.