Macrophages as effector cells of protective immunity in murine schistosomiasis: macrophage activation in mice vaccinated with radiation-attenuated cercariae

Individually or as a Team-The Immunological Milieu in the Lung Caused by Migrating Single-Sex or Mixed-Sex Larvae of Schistosoma mansoni

While the lung is considered an efficient site for stopping the larvae of the acute Schistosoma spp. infection phase from migrating through extensive inflammatory responses in the surrounding tissues, little is known about these processes. To date, the highest resistance to infection has been achieved in experimental studies with radiation-attenuated cercariae immunization, which elicits a strong Th1/Th2 response in the lung and results in up to 80% protection. Based on our own studies demonstrating a systemic, unpolarized Th1/Th2 response resulting from infection with male or female Schistosoma mansoni, we hypothesize that this atypical immune response is already detectable during the pulmonary passage of parasite larvae. Therefore, we examined the immune milieu in the lungs of mice caused by migrating schistosome larvae, either male or female (single-sex groups) or male + female (bisexual control), 4 and 16 days after infection in bronchoalveolar lavage and lung tissue by flow cytometry, qPCR, and multiplex analyzes. Our results show only minor differences in the inflammatory profile between the single-sex groups but significant differences compared with the bisexual control group. Both single-sex infected groups have increased expression of inflammatory markers in lung tissue, higher numbers of cytotoxic T cells (day 4 post-infection) and more T helper cells (day 16 post-infection), compared with the bisexual control group. A single-sex infection, regardless of whether it is an infection with male or female cercariae, causes an immune milieu in the lung that is clearly different from an infection with both sexes. In terms of identifying therapeutic targets to achieve resistance to re-infection, it is of great scientific interest to identify the differences in the inflammatory potential of male or female and male + female parasites.

Schistosomes in the Lung: Immunobiology and Opportunity

Schistosome infection is a major cause of global morbidity, particularly in sub-Saharan Africa. However, there is no effective vaccine for this major neglected tropical disease, and re-infection routinely occurs after chemotherapeutic treatment. Following invasion through the skin, larval schistosomula enter the circulatory system and migrate through the lung before maturing to adulthood in the mesenteric or urogenital vasculature. Eggs released from adult worms can become trapped in various tissues, with resultant inflammatory responses leading to hepato-splenic, intestinal, or urogenital disease – processes that have been extensively studied in recent years. In contrast, although lung pathology can occur in both the acute and chronic phases of schistosomiasis, the mechanisms underlying pulmonary disease are particularly poorly understood. In chronic infection, egg-mediated fibrosis and vascular destruction can lead to the formation of portosystemic shunts through which eggs can embolise to the lungs, where they can trigger granulomatous disease. Acute schistosomiasis, or Katayama syndrome, which is primarily evident in non-endemic individuals, occurs during pulmonary larval migration, maturation, and initial egg-production, often involving fever and a cough with an accompanying immune cell infiltrate into the lung. Importantly, lung migrating larvae are not just a cause of inflammation and pathology but are a key target for future vaccine design. However, vaccine efforts are hindered by a limited understanding of what constitutes a protective immune response to larvae. In this review, we explore the current understanding of pulmonary immune responses and inflammatory pathology in schistosomiasis, highlighting important unanswered questions and areas for future research.

Evaluation of the protective immune response induced in mice by immunization with Schistosoma mansoni schistosomula tegument (Smteg) in association with CpG-ODN

In schistosomiasis, the current control strategy does not prevent reinfection, therefore, vaccine strategies are essential to combat the Schistosoma mansoni. The efficacy vaccine depends on parasite stage and effective adjuvant. We have recently demonstrated that S. mansoni schistosomula tegument (Smteg) is able to activate dendritic cells up regulate CD40 and CD86 molecules and induce a partial protection in mice (43-48%) when formulated with Freund's adjuvant. In this study we evaluated the ability of Smteg + alum or Smteg + alum + CpG-ODN to induce protection in mice. Our results demonstrate that Smteg + alum + CpG-ODN induced a partial reduction in worm burden (43.1%), reduction in the number of eggs eliminated in the feces. The protective response was associated with a predominant Th1 type of immune response, with increased production of specific IgG2c, IFN-γ and TNF-α, B cells proliferation and CD4 cells and macrophages activation.

Characterization and vaccination of two novel Schistosoma japonicum genes screened from a cercaria cDNA library

Two novel genes, SJCWL05 and SJCWL06, were harvested from screening of Schistosoma japonicum (S. japonicum) cercaria cDNA library by using pig sera vaccinated (VPS) with S. japonicum immature egg ws-vaccine (S. japonicum iEw). Prokaryotic recombinant plasmids pGEX-4T-1/SJCWL05 and pGEX-4T-1/SJCWL06 were constructed to analyze their immunogenicity, which was confirmed by SDS-PAGE and Western blotting. Two eukaryotic recombinant plasmids, pcDNA3/SJCWL05 and pcDNA3/SJCWL06, were constructed, and their ability to protect mice against challenge of S. japonicum was evaluated. All mice vaccinated with pcDNA3/SJCWL05 or pcDNA3/SJCWL06 developed ELISA-specific anti-S. japonicum SIEA (S. japonicum soluble immature egg antigens) antibody. Immunoprotection experiments showed that worms and liver eggs reduced 34.64% and 39.14% in the pcDNA3/SJCWL05 group and those reduced 27.17% and 27.95% in the pcDNA3/SJCWL06 group, respectively. The reduction rates of intestine and uterine eggs in female worms of both groups reached 39.45% and 38.5% as well as 30.02% and 28.7%, respectively. Results of our study suggest that novel genes, SJCWL05 and SJCWL06, are potential vaccine candidates against schistosomiasis japonica.

A Schistosoma japonicum chimeric protein with a novel adjuvant induced a polarized Th1 immune response and protection against liver egg burdens

Background

Schitosomiasis japonica is still a significant public health problem in China. A protective vaccine for human or animal use represents an important strategy for long-term control of this disease. Due to the complex life cycle of schistosomes, different vaccine design approaches may be necessary, including polyvalent subunit vaccines. In this study, we constructed four chimeric proteins (designated SjGP-1~4) via fusion of Sj26GST and four individual paramyosin fragments. We tested these four proteins as vaccine candidates, and investigated the effect of deviating immune response on protection roles in mice.

Methods

The immunogencity and protection efficacy of chimeric proteins were evaluated in mice. Next, the chimeric protein SjGP-3 was selected and formulated in various adjuvants, including CFA, ISA 206, IMS 1312 and ISA 70M. The titers of antigen-specific IgG, IgE and IgG subclass were measured. The effect of adjuvant on cytokine production and percentages of CD3⁺CD8^-IFN-γ⁺ cells and CD3⁺CD8^-IL-4⁺ cells were analyzed at different time points. Worm burdens and liver egg counts in different adjuvant groups were counted to evaluate the protection efficacy against cercarial challenge.

Results

Immunization of mice with chimeric proteins provided various levels of protection. Among the four proteins, SjGP-3 induced the highest level of protection, and showed enhanced protective efficacy compared with its individual component Sj26GST. Because of this, SjGP-3 was further formulated in various adjuvants to investigate the effect of adjuvant on immune deviation. The results revealed that SjGP-3 formulated in veterinary adjuvant ISA 70M induced a lasting polarized Th1 immune response, whereas the other adjuvants, including CFA, ISA 206 and IMS 1312, generated a moderate mixed Th1/Th2 response after immunization but all except for IMS 1312 shifted to Th2 response after onset of eggs. More importantly, the SjGP-3/70M formulation induced a significant reduction in liver egg deposition at 47.0–50.3% and the number of liver eggs per female at 34.5–37.2% but less effect on worm burdens at only 17.3–23.1%, whereas no effect of the formulations with other adjuvants on the number of liver eggs per female was observed.

Conclusion

Construction of polyvalent subunit vaccine was capable to enhance immunogenicity and protection efficacy against schistosomiasis. There was correlation of the polarized Th1 response with reduction of liver egg burdens, supporting the immune deviation strategy for schistosomiasis japonica vaccine development.

Immunomodulatory effects of curcumin treatment on murine schistosomiasis mansoni

Curcumin is a polyphenol derived from the dietary spice turmeric. It has been shown to regulate numerous transcription factors, cytokines, adhesion molecules, and enzymes that have been linked to inflammation. In addition to inhibiting the growth of a variety of pathogens, curcumin has been shown to have nematocidal activity. The present study was designed to evaluate the schistosomicidal activity of curcumin in vivo as well as immunomodulation of granulomatous inflammation and liver pathology in acute schistosomiasis mansoni. Mice were infected each with 80 Schistosoma (S.) mansoni cercariae and injected intraperitoneally with curcumin at a total dose of 400mg/kg body weight. Curcumin was effective in reducing worm and tissue-egg burdens, hepatic granuloma volume and liver collagen content by 44.4%, 30.9%, 79%, and 38.6%, respectively. Curcumin treatment restored hepatic enzymes activities to the normal levels and enhanced catalase activity in the liver tissue of infected mice. Moreover, hepato-spleenomegaly and eosinophilia induced by S. mansoni infection were largely improved with curcumin treatment. Infected mice treated with curcumin showed low serum level of both interleukin (IL)-12 and tumor necrosis factor alpha (TNF-alpha), but IL-10 level was not significantly altered. Specific IgG and IgG1 responses against both soluble worm antigen (SWAP) and soluble egg antigen (SEA) were augmented with curcumin treatment, but IgM and IgG2a responses were not significantly changed. In conclusion, curcumin treatment modulates cellular and humoral immune responses of infected mice and lead to a significant reduction of parasite burden and liver pathology in acute murine schistosomiasis mansoni.

Chronic intestinal nematode infection exacerbates experimental Schistosoma mansoni infection

Mixed-parasite infections are common in many parts of the world, but little is known of the effects of concomitant parasite infections on the immune response or on disease progression. We have investigated the in vivo effects of a chronic gastrointestinal nematode infection on the infectivity and development of the immune response against the common trematode helminth Schistosoma mansoni. The data show that mice carrying an established chronic Trichuris muris infection and coinfected with S. mansoni, had significantly higher S. mansoni worm burdens than mice without coinfection. The increase in S. mansoni worm burden was accompanied by a higher egg burden in the liver. Kinetic analysis of S. mansoni establishment indicate reduced trapping of S. mansoni larvae during skin-to-lung migration, with T. muris-induced alterations in lung cytokine expression and inflammatory foci surrounding lung-stage schistosomula, suggesting that the immunomodulatory effects of chronic T. muris infection elicited at the gut mucosal surface extend to other organs and perhaps specifically to other mucosal surfaces. The data show that a preexisting chronic gastrointestinal nematode infection facilitates the survival and migration of S. mansoni schistosomula to the portal system, and as a result, increases the egg burden and associated pathology of S. mansoni infection.

Schistosoma japonicum: localization of calpain in the penetration glands and secretions of cercariae

A monoclonal antibody was generated against the large subunit of Schistosoma japonicum calpain to study the localization and possible function of the molecule in vivo. Mice were immunized with recombinant S. japonicum calpain and polyclonal antisera and a monoclonal antibody specific to schistosome calpain was obtained. In immunohistochemistry, a monoclonal antibody against S. japonicum calpain, KG-2E11, bound weakly to calpain expressed at the surface of adult worm tegument, however, it bound strongly to the cercarial secretions ("footprints") of S. japonicum, emitted from the penetration glands. The present study indicates that calpain is multifunctional as it is expressed at various locations in different developmental stages. Calpain-based vaccines could thus possibly induce protective immunity against cercariae and the following early developing stages.

Immunisation with Salmonella typhimurium-delivered glyceraldehyde-3-phosphate dehydrogenase protects mice against challenge infection with Echinococcus multilocularis eggs

Recombinant glyceraldehyde-3-phosphate dehydrogenase of the cestode parasite Echinococcus multilocularis was expressed in Escherichia coli and in Salmonella typhimurium. The potential of different forms of the recombinant antigen to protect BALB/c mice against oral challenge infections with E. multilocularis eggs was evaluated. Oral or intraperitoneal immunisation with live attenuated S. typhimurium as a carrier for recombinant glyceraldehyde-3-phosphate dehydrogenase of the E. multilocularis resulted in significant protection, reducing the number of developing metacestodes up to 79.8%. The sera of protected animals did not contain detectable amounts of antibody against glyceraldehyde-3-phosphate dehydrogenase of E. multilocularis. By contrast, although anti-glyceraldehyde-3-phosphate dehydrogenase of E. multilocularis antibodies were detectable in the sera, immunisation with E. coli-expressed recombinant glutathione-S-transferase-fusion protein or with glyceraldehyde-3-phosphate dehydrogenase of E. multilocularis fused to a 6HIS-tag failed to protect the animals against oral challenge infections. These data emphasise that antigen delivery systems play a critical role in vaccination and the induction of protective immunity against helminth parasites.

Vaccination with calpain induces a Th1-biased protective immune response against Schistosoma japonicum

A large subunit of calpain, a calcium-activated neutral proteinase, from Schistosoma japonicum was cloned and expressed in Escherichia coli. When BALB/c mice were immunized with purified recombinant calpain (r-calpain) emulsified in complete Freund's adjuvant, a significant reduction in the number of recovered worms and also in egg production per female worm was observed (P<0.01). Spleen cells of the immunized mice showed enhanced production of gamma interferon (IFN-gamma) by activated CD4(+) T cells. Considering our observation of elevated expression of inducible nitric oxide synthase mRNA in immunized mice, r-calpain-induced IFN-gamma seemed to upregulate the production of nitric oxide by macrophages and subsequently mediated the killing of schistosomulae in the lung. On the other hand, spleen cells of immunized mice showed only faint interleukin-4 production in response to r-calpain in vitro, suggesting that immunization with r-calpain alters the Th1-Th2 balance in murine hosts even during a Th2-promoting S. japonicum infection. Furthermore, histopathological study of the livers of immunized mice showed that granulomas formed around eggs were diminished in both size and number. Egg production by female worms was clearly decreased in immunized mice, suggesting that r-calpain also has antifecundity effects. Taken together, these results point to S. japonicum calpain as a potential vaccine candidate for both worm killing and disease prevention, possibly through the induction of a strong Th1-dominant environment in immunized mice.

Optimal Vaccination Against Schistosoma mansoni Requires the Induction of Both B Cell- and IFN-γ-Dependent Effector Mechanisms

Mice immunized with radiation-attenuated cercariae of Schistosoma mansoni display resistance to challenge infection, which increases with multiple boosting. Protection in animals receiving a single vaccination is thought to involve a primarily cell-mediated, IFN-γ-dependent mechanism, while humoral immunity has been shown to contribute to challenge rejection in multiply (three times) immunized mice. To better understand the respective contribution of the B lymphocyte- and IFN-γ-dependent effector arms in host resistance, we compared vaccine-induced immunity in B cell-deficient (μMT) and IFN-γ knockout (GKO) animals. Unexpectedly, after a single vaccination, B cell knockout (KO) mice displayed reduced protection against challenge infection, although they developed a normal IFN-γ-dominated cytokine response. This defect in resistance was equivalent to that displayed by GKO animals. Moreover, whereas two additional vaccinations significantly increased the level of immunity in wild-type mice, the protection in B cell KO animals remained unchanged. In contrast, multiple vaccination resulted in increased but, nevertheless, defective resistance in GKO mice. Since FcR γ KO mice, which lack functional FcγRI, FcγRIII, and FcεRI, show no defects in vaccine-induced resistance after immunization either one or three times, the B cell-dependent mechanism of protection involved does not appear to require FcR signaling. Together, these findings indicate that effective vaccination against schistosomes depends on the simultaneous induction of both humoral and cell-mediated immunity, a conclusion that may explain the limited success of most subunit vaccine protocols designed to preferentially induce either B cell- or IFN-γ-dependent protective mechanisms.

Electron and light microscopy of peritoneal cellular immune responses in mice vaccinated and challenged with third-stage infective hookworm (Ancylostoma caninum) larvae

The role of peritoneal macrophages in a murine model of immunity to living hookworm third-stage larvae (L3) was investigated. Mice immunized orally with 500 L3 once every 2 weeks for three times were challenged intraperitoneally with 2000 L3 1 week after the final immunization. The challenged larvae were collected from the peritoneal cavity at intervals between 2 and 72 h and then examined by inverted light microscopy, scanning electron microscopy and transmission electron microscopy. Peritoneal cellular responses in non-immunized mice served as negative controls. The numbers of peritoneal macrophages in immunized mice were 6-7-fold higher than in non-immunized mice. In the peritoneal cavity of immunized mice, host macrophages adhered to the challenged L3 within 2 h and created a cocoon-like encasing which surrounded the parasite. Extensive damage to the L3 was observed which included swelling, collapse and deformation of the larval cuticle. Lysis and vacuolization of the parasite's internal structures were also observed. In contrast, no significant cellular adherence and damage were observed in L3 recovered from non-immunized mice. L3-specific antibody levels were also elevated in the peritoneum of immunized mice relative to non-immunized controls. These studies implicate macrophages as important effector cells in hookworm larval vaccine immunity.

The debate over the effector function of eosinophils in helminth infection: new evidence from studies on the regulation of vaccine immunity by IL-12

The production of Th1-type cytokines is associated with strong cell-mediated immunity while Th2-type cytokines are typically involved in the generation of humoral immune responses. In mice vaccinated a single time (1X) with attenuated cercariae of Schistosoma mansoni, the immunity induced is highly dependent on CD4+ T cells and IFN-gamma. In contrast, mice vaccinated multiple times (3X) have decreased IFN-gamma expression, develop a more dominant Th2-type cytokine response as well as protective antibodies which can passively transfer immunity to naive recipients. Previously, we demonstrated the ability of IL-12, a potent IFN-gamma-inducing cytokine to enhance (1X) schistosome cell-mediated saline-treated mice demonstrated a 70 immunity when administered during the period of immunization. More recently, we asked what effects IL-12 would have on the development humoral-based immunity. While multiply-immunized/ saline-treated mice demonstrated a 70-80% reduction in parasite burden, 3X/IL-12-vaccinated animals displayed an even more striking > 90% reduction in challenge infection, with many mice in the later group demonstrating complete protection. Analysis of pulmonary cytokine mRNA responses demonstrated that control challenged mice elicited a dominant Th2-type response, 3X/saline-vaccinated produced a mixed Th1/Th2-type cytokine response, while 3X/IL-12-immunized animals displayed a dominant Th1-type response. The IL-12-treated group also showed a marked reduction in total serum IgE and tissue eosinophilia while SWAP-specific IgG2a and IgG2b Abs were elevated. Interestingly, animals vaccinated with IL-12 also showed a highly significant increase in total Ig titers specific for IrV, a known protective antigen. More importantly, 3X/IL-12 serum transferred significantly less protection. Nevertheless, animals vaccinated in the presence of IL-12 also develop macrophages with enhanced nitric oxide dependent killing activity against the parasites. Together, these observation suggest that IL-12, initially described as an adjuvant for cell-mediated immunity, may also be used as an adjuvant for promoting both humoral and cell-mediated protective responses.

Role of nitric oxide in parasitic infections

Nitric oxide is produced by a number of different cell types in response to cytokine stimulation and thus has been found to play a role in immunologically mediated protection against a growing list of protozoan and helminth parasites in vitro and in animal models. The biochemical basis of its effects on the parasite targets appears to involve primarily inactivation of enzymes crucial to energy metabolism and growth, although it has other biologic activities as well. NO is produced not only by macrophages and macrophage-like cells commonly associated with the effector arm of cell-mediated immune reactivity but also by cells commonly considered to lie outside the immunologic network, such as hepatocytes and endothelial cells, which are intimately involved in the life cycle of a number of parasites. NO production is stimulated by gamma interferon in combination with tumor necrosis factor alpha or other secondary activation signals and is regulated by a number of cytokines (especially interleukin-4, interleukin-10, and transforming growth factor beta) and other mediators, as well as through its own inherent inhibitory activity. The potential for design of prevention and/or intervention approaches against parasitic infection (e.g., vaccination or combination chemo- and immunotherapy strategies) on the basis of induction of cell-mediated immunity and NO production appears to be great, but the possible pathogenic consequences of overproduction of NO must be taken into account. Moreover, more research on the role and regulation of NO in human parasitic infection is needed before its possible clinical relevance can be determined.

Immunity after treatment of human schistosomiasis: association between cellular responses and resistance to reinfection

Previous studies have demonstrated the development of an age-dependent resistance to reinfection after chemotherapeutic cure of the helminthic parasite Schistosoma mansoni. Here we report on a longitudinal investigation of cell-mediated responses in infected individuals before and after treatment which was designed to outline those parameters important in mediating a protective response. A well-defined study group of 89 individuals with an age range of 9 to 35 years was selected from an area of high S. mansoni transmission in the Machakos district of Kenya. Peripheral blood mononuclear cell proliferation and cytokine production (interleukin-2 [IL-2], gamma interferon IL-5, IL-4, and tumor necrosis factor) in response to different crude life cycle-stage antigens of S. mansoni were assessed longitudinally in vitro before, 3 months after, and 1 year after treatment. Detailed statistical analyses of the results from this study have indicated a clear negative association between the proliferative responses to adult- and schistosomulum-stage antigens and subsequent reinfection intensity in older individuals (14 to 35 years) which was not present in the younger individuals (9 to 13 years). This association was significant even after the effects of age, sex, and exposure had been accounted for in multiple regression analyses. Cytokines were detected predominantly in response to adult worm and egg antigen extracts. An inverse association between the two cytokines gamma interferon and IL-5 was detected in response to all antigens at the three time points investigated, indicating cross-regulation in the production of these two mediators. Differences in antigen-specific cytokine levels between the two age groups were detected, with significantly higher IL-5 levels detected in the older (more resistant) age group. An inverse correlation between this cytokine and reinfection was detected but could not be dissociated from the effects of age and exposure in multiple regression analysis.

Experimental models of immunization against schistosomes: lessons for vaccine development

Schistosomiasis is a debilitating, and sometimes deadly, parasitic infection that afflicts hundreds of millions of people living in developing countries. One of the best hopes for control of this disease is vaccine development. Studies on experimental models of attenuated vaccines have proven that high levels of protective immunity can be achieved. In these systems, resistance has been shown to be directed against the migrating larval stages of the parasite and to have both cellular and humoral components. Several candidate vaccine immunogens have been identified on the basis of antibody reactivity. However, the level of protection induced by immunization with nonliving vaccines has at yet not approached the level observed with attenuated infection. Current challenges to vaccine development include identification of protective T cell immunogens, determination of ways to strengthen the immunogenicity of isolated parasite antigens, and development of methodologies to selectively stimulate protective, as opposed to ineffective or even detrimental, immune responses.

Larvicidal properties of macrophages induced by cloned murine schistosomal egg antigen-specific CD4 positive T-helper lymphocytes

The role of T-helper (TH) lymphocytes in activating peritoneal macrophages (PM) to kill larvae of the helminth Schistosoma mansoni (schistosomula) was investigated with the use of egg antigen-specific CD4 positive TH clones of both the TH1 and TH2 types. Results showed that stimulated TH1 clones, in exceedingly small numbers, or supernatants thereof, conferred on PM the ability to kill schistosomula. The molecule responsible for PM activation was found to be interferon-gamma (IFN-gamma). IFN-gamma-induced PM larvicidal activity was dependent on live cells, energy, as well as protein synthesis, and appeared to be mediated by toxic nitrogen metabolites. In contrast, egg antigen-specific TH2 clones, or their supernants, failed to induce PM larval killing, as they did not secrete IFN-gamma, or any equivalent macrophage activating factor. We postulate a mechanism by which egg antigen-specific TH1 clones may be capable of playing a critical role in the resistance to schistosomal reinfection through IFN-gamma-mediated activation of macrophage helminthotoxicity.

Activated macrophages in highly irradiated cercariae-induced immunity to Schistosoma japonicum in rats

The results of studies on the schistosomulicidal activity of activated peritoneal and alveolar macrophages (pM phi and aM phi) from rats immunized with highly irradiated (50 krad.) Schistosoma japonicum cercariae are reported. The authors have examined the activation of these macrophages in terms of spreading, adhesion and ingestion of sheep erythrocytes and pinocytosis of horse-radish peroxidase. Using three criteria, peritoneal macrophages and alveolar macrophages from immunized rats and from rats intraperitoneally injected with BCG were significantly more active than those from normal rats or rats stimulated with 10% proteose-peptone or 1% sodium thioglycolate. A significantly higher percentage of adhesion and ingestion was obtained with the sheep erythrocytes that were co-opsonized by heat-inactivated rat anti-sheep erythrocyte serum and fresh normal rat serum. Schistosomulicidal effects were observed with macrophages from irradiated cercariae-immunized rats in two activation systems: in vitro activation in the presence of macrophage-activating factor (MAF), and in vivo activation by the intraperitoneal challenge with sonicated cercarial antigens.

Schistosoma mansoni larvicidal activity of murine bronchoalveolar lavage cells

We have investigated the ability of cells obtained from both normal and immune mice by bronchoalveolar lavage (BACs) to kill Schistosoma mansoni larvae in vitro. In cultures with mechanically derived schistosomules, high levels of larvicidal activity were displayed by BACs from both normal and irradiated cercaria-immunized C57BL/6 mice. Based on effector-to-target-cell ratios, BAC-mediated killing was two- to threefold more efficient than killing mediated by macrophage-rich cell populations obtained from the peritoneal cavity. BACs from normal A/J mice were essentially as larvicidal as normal C57BL/6 cells. However, BACs from a strain of mouse (P/J) with a known macrophage defect possessed negligible larvicidal activity. Macrophages made up 85 to 95% of BACs from all three strains tested. In contrast to cells of the IC-21 macrophage cell line, B6 BACs did not show enhanced killing activity when preincubated with lymphokine-containing supernatants. Lung schistosomules harvested 10 days after cercarial penetration were refractory to BAC-mediated killing.

Lung-phase immunity to Schistosoma mansoni: definition of alveolar macrophage phenotypes after vaccination and challenge of mice

Phenotypic changes in murine alveolar macrophages have been described in response to vaccination with irradiated cercariae and to a subsequent challenge with normal parasites. Flow cytometric analysis was used to quantify the proportions of cells strongly positive for a number of macrophage surface markers, detected by a panel of monoclonal primary antibodies and fluorescent secondary antibodies. The proportion of Ia+ macrophages sampled by bronchoalveolar lavage increased 5-fold over days 14 to 28 post-vaccination. This upregulation of Ia was accompanied by a sharp decrease in F4/80 expression between days 14 and 21. The low percentage of F4/80+ cells persisted for several weeks after vaccination, and no further change was stimulated by challenge parasites. These altered characteristics are consistent with the 'activation phenotype' induced by other infectious agents. After challenge of immune mice, further changes in macrophage phenotype were slight compared to the responses elicited by vaccination, or to those induced in the challenge control group; Ia expression increased to about three times normal levels. The phenotypic changes correspond both in magnitude and timing with the pattern of alveolar macrophage activation determined in a previous study. The limited changes in phenotype of alveolar macrophages from immunized mice after challenge could indicate that these cells become refractory to reactivation. Overall, the altered macrophage phenotype after vaccination and challenge provides circumstantial evidence for the action of cytokines, particularly interferon-gamma, in lung-phase immunity to schistosomes.

Tumour necrosis factor (TNF) as a mediator of macrophage helminthotoxic activity

Lymphokine-activated macrophages are cytotoxic for larvae of the helminth parasite Schistosoma mansoni. That soluble secreted factors may mediate this cytotoxicity was suggested by the observation that culture supernatant fluids from stimulated macrophages also exhibited larvacidal activity. These fluids contain the monokine tumour necrosis factor (TNF). Several observations indicated that TNF is directly toxic to schistosome larvae. Cytotoxic sera taken from BCG- or S. mansoni-immunized mice after endotoxin challenge killed schistosomula in vitro, and upon gel filtration the larvacidal factor(s) in the sera co-eluted with the tumoricidal activity defined as TNF. Recombinant-derived TNF exhibited direct toxicity to schistosomula at high concentrations, or at lower concentrations in the presence of IFN gamma. The larvacidal activity of macrophage supernatant fluids was abrogated by addition of either anti-TNF antisera or Zn+2, which has been shown to inhibit TNF-induced damage of tumour cells. Anti-TNF and Zn+2 likewise suppressed schistosomulum killing by lymphokine-activated peritoneal macrophages or the IC-21 macrophage line, indicating that TNF also plays a role in the effector mechanism of larval killing by whole cells.

Cytotoxic effects in vitro of human monocytes and macrophages on schistosomula of Schistosoma mansoni

Human peripheral blood monocytes from normal donors were isolated by differential centrifugation and cultured in vitro in hydrophobic Teflon-coated tissue culture bags. Cells were harvested between 0 and 10 days and tested for their ability to kill schistosomula of Schistosoma mansoni in an in-vitro cytotoxicity assay. Freshly isolated, unstimulated monocytes demonstrated minimal cytotoxic capability. However, this was increased if the cells were pretreated with human recombinant gamma interferon (IFN-gamma), or with specific anti-S. mansoni antiserum. As the monocytes matured in vitro there were marked increases in the levels of antibody-independent killing of schistosomula. Monocytes grown in vitro with IFN-gamma (10(4) u/ml) took 2-3 days to develop almost maximal cytotoxicity (mean 94% kill of schistosomula). In contrast, unstimulated monocytes (no IFN-gamma) took between 5 and 7 days to achieve comparable cytotoxicity (mean 99% kill). Killing of the schistosomula was dependent upon a high effector to target ratio, and was a relatively slow phenomenon in vitro, parasite attrition occurring between 17 and 36 h. Supernatants from cytotoxic macrophages were ineffective in mediating cytotoxicity of the parasite.

Immunity to Schistosoma mansoni in guinea-pigs vaccinated with radiation-attenuated cercariae. T-cell activation of macrophages for larval killing

This study addresses macrophage activation in guinea-pigs vaccinated with radiation-attenuated cercariae of Schistosoma mansoni. Peritoneal exudate macrophages elicited in vaccinated animals by mineral oil injection were activated to kill larval schistosomes in vitro. Killing efficiency is dependent upon the cell: target ratio employed and is enhanced by, but is not strictly dependent on, the presence of specific antibodies. Macrophages co-cultured with parasites release superoxide radicals and hydrogen peroxide, but the use of inhibitors has shown that neither of these reactive oxygen intermediates are the causal agents of cellular cytotoxicity in this system. Oil-elicited macrophages from naive guinea-pigs do not show comparable activation; they can, however, be activated in vitro by incubation with culture supernatant fluids from schistosome antigen-stimulated spleen, or lymph node cells harvested from vaccinated guinea-pigs. Naive macrophages activated in this way kill schistosomula in vitro and release the activation markers IL-1 and superoxide anion. The macrophage-activating factor (MAF) present in spleen cell culture supernatant fluids has a MW of 35,000-55,000, but does not have the chemical characteristics of gamma-interferon. In this study MAF is shown to be released by a population of lymph node cells that does not adhere to nylon-wool columns, that responds well in proliferation assays to schistosome antigens and to the T-cell mitogen concanavalin A, but does not respond to the B-cell mitogen lipopolysaccharide. These cells have been identified as small lymphocytes.

Studies on immunity to Schistosoma mansoni in vivo: whole-body irradiation has no effect on vaccine-induced resistance in mice

Actively immunized mice, whole-body irradiated with 650 or 525 rad., manifested comparable levels of resistance to Schistosoma mansoni compared with unirradiated, immunized mice in spite of a marked reduction in circulating leucocytes (greater than 90%) and platelets (greater than 85%), and despite an abrogation of delayed-type hypersensitivity (DTH) (Type IV) response to schistosomular antigens (as determined by footpad swelling, 24 h after injection of antigen). However, limited histopathological comparison of lung sections from irradiated and unirradiated mice 7 days post-challenge showed that cellular reactions ('foci') around parasites were essentially similar in size and cellular composition except that in irradiated mice, eosinophils were poorly represented both in the foci and in lung tissue in general. Neither presumed immune complex-mediated (Type III, Arthus reaction) hypersensitivity (as determined by footpad swelling, 5 h after injection of antigen) nor serum anti-schistosomulum extract antibody levels (as determined by ELISA) were affected. In addition, the pattern of 125I-labelled schistosomular surface antigens immunoprecipitated with serum from irradiated and unirradiated mice was essentially similar. These results are consistent with antibody playing an important role in vaccine-induced immunity in mice but suggest that radiosensitive T cell function and radiosensitive cells, such as platelets and polymorphonuclear cells, including eosinophils, may not be essential.

Immunity after treatment of human schistosomiasis mansoni quantitative and qualitative antibody responses to tegumental membrane antigens prepared from adult worms

Quantitative antibody responses of individual Kenyan children to a tegument membrane preparation from adult schistosomes have been studied by enzyme-linked immunosorbent assay. Qualitative differences between patients were examined by electrophoretic fractionation of the membrane preparation followed by Western blotting analysis. All individuals had antibodies to the preparation, the level increasing twofold shortly after chemotherapy and declining to pre-treatment levels by 6 months. Susceptible children had significantly higher levels of antibody than resistant individuals at 12 and 18 months after chemotherapy. Antibody levels were positively associated with patient age (particularly over the range 8-12 years at the first bleed after chemotherapy) and the logarithm of pre-treatment egg excretion. The strongest association was observed between initial antibody level and subsequent levels. A total of 47 distinct antigens was detected in the membrane preparation. The major antigens were detected equally strongly by sera from both susceptible and resistant groups of children. At the outset the resistant group responded more strongly to 35%, and more weakly to 15%, of the antigens than the susceptible group. At the end of the study the figures were reversed, being 21% and 38% respectively, probably reflecting the reflecting the reinfection of the susceptible group. 3 antigens of molecular mass 100, 50 and 27 kDa were exceptions to the trend, being detected more strongly by the resistant than the susceptible group at one or more later times. It was concluded that the differences in total antibody level to the tegument membrane preparation were insufficient to account for the resistant or susceptible status of the children.

Macrophage activation as an immune correlate to protective immunity against schistosomiasis in mice immunized with an irradiated, cryopreserved live vaccine

Immune responses against Schistosoma mansoni were evaluated in C57BL/6 mice injected with one of two populations of irradiated schistosomules, the larval preparations differing only in the degree of freezing-induced damage sustained upon cryopreservation. Mice injected with larvae which successfully withstood cryopreservation showed a significant reduction in worm burden following cercarial challenge. No protection was achieved in mice which received larvae damaged by a suboptimal thawing rate. Parallel comparison of several humoral and cellular responses in mice which received either inoculum revealed that induction of activated macrophages and production of macrophage-activating lymphokine activity were the strongest correlates to development of protective immunity. Protected mice also showed marginal 30-min skin test reactivity and weak but transient 24-h delayed-type hypersensitivity to a soluble adult worm preparation. In contrast, indistinguishable levels of circulating antibodies to soluble and tegumental antigens developed in the two immunization groups, and antigen-stimulated lymphocyte blastogenic responses were strong and essentially equivalent in magnitude. These studies strongly suggested that in this new model for investigating anti-schistosome effector mechanisms, responses contributing to the development of activated macrophages may be essential for induction of protective immunity.

Stimulation of macrophage tumoricidal activity by the growth and differentiation factor CSF-1

The effect of the macrophage growth and differentiation factor CSF-1 on the tumoricidal capacity of murine peritoneal exudate macrophages was investigated. Pretreatment of peptone-elicited macrophages 1 day with 300-1200 U/ml CSF-1 induced moderate killing and greatly stimulated lymphokine (LK)-induced killing of [3H]thymidine-labeled TU5 sarcoma cells to levels above that seen with fresh macrophages. Further addition of CSF-1 at Day 1 at the time of the tumor lysis assay promoted moderate increases in spontaneous and LK-induced activity. CSF-1 did not stimulate freshly harvested exudate macrophages to lyse TU5 targets in the presence or absence of lymphokine (LK) activators. Lipopolysaccharide (LPS) at 0.1-1000 ng/ml did not stimulate cytotoxicity, and the low endotoxin content and the use of polymyxin B and C3H/HeJ mice excluded a role for LPS in these experiments. Incubation of the macrophages with IFN and the myeloid growth factors IL-3 and GM-CSF did not stimulate tumoricidal activity. CSF-1 has been proposed as a therapeutic agent to restore myeloid cell numbers in induced (cancer chemotherapy, bone marrow transplantation, etc.) and natural aplastic anemias. These studies show that CSF-1 also may be useful in combination with LK activators to promote resistance to cancer in mature mononuclear cells. CSF-1 may have similar effects in LK-activated macrophages to enhance resistance to infectious diseases.

Immunity to schistosomiasis mansoni in guinea-pigs vaccinated with radiation-attenuated cercariae: I. Humoral responses against skin-stage schistosomula

The anti-schistosomular humoral responses of guinea-pigs vaccinated with radiation-attenuated cercariae of Schistosoma mansoni have been investigated in vitro. The sera of vaccinated animals contain schistosomulicidal complement-fixing antibodies which peak in titre at week 5 after vaccination and predominantly consist of IgG2 and IgM antibodies. The ability of the serum to arm macrophages from normal animals to bind to schistosomula, also peaks in titre at week 5 and is associated with IgG2 antibodies. Basophils from normal animals can be sensitized in vitro by vaccine serum to degranulate in the presence of schistosomular antigens. This anaphylactic antibody activity is associated with IgG1 but not IgE antibodies, and peaks in titre at week 10. Three antigens (14 kD, 20 kD and 43 kD) are specifically and transiently detected by vaccine serum on Western blots of schistosomular proteins; these antigens are first discernible at week 4, but were virtually undetectable at week 12.

Post lung-stage schistosomula of Schistosoma mansoni exhibit transient susceptibility to macrophage-mediated cytotoxicity in vitro that may relate to late phase killing in vivo

Studies of protective immunity against Schistosoma mansoni in immunized mice suggest that a proportion of challenge parasites may be eliminated after they have passed through the lungs of the host several days after infection; however, no potential immune effector mechanism of resistance against this stage of the parasite has yet been identified, since schistosomes have been shown to rapidly become resistant to antibody-dependent killing mechanisms. In this study, different development stages of S. mansoni were examined for their susceptibility to in vitro cytotoxicity by lymphokine-activated macrophages. As previously shown, newly transformed larvae were readily killed by lymphokine-treated peritoneal macrophages or the macrophage cell line IC-21 (80% mortality over 48 h in vitro), whereas 7 and 10 day old lung-stage parasites had become refractory to macrophage effects. However, after 2 to 2 1/2 weeks of development in vivo, juvenile parasites recovered from the liver were again susceptible to activated macrophage-mediated cytotoxicity (25-65% mortality). Ultrastructural studies of 2 1/2 week old parasites co-cultured with activated IC-21 cells revealed that damage was largely restricted to the areas beneath the parasite surface and gut syncitia; surface membrane disruption was not evident. This late stage of susceptibility was transient and by 4 to 6 weeks liver-stage worms had again become refractory to macrophage killing. The interaction of post lung-stage parasites with activated macrophages was antibody independent. Furthermore, schistosomes isolated from the portal circulation 2 1/2 weeks after infection showed no evidence of surface-bound immunoglobulin in a quantitative immunofluorescence assay, nor did antisera from chronically infected mice (CIS) or mice vaccinated with irradiated cercariae (VS) react with the surface of these parasites in vitro, making the possibility of direct antibody-dependent killing mechanisms unlikely. However, both CIS and VS did recognize excretory/secretory proteins synthesized by 2 1/2 week old liver-stage schistosomes, including a major antigen of approximate Mr (X 10(-3] 220 (220K). It is therefore possible that such antigens might participate in protective immunity, for example via immune complex formation or activation of sensitized T cells. These observations support the role of macrophages as immune effector cells in mice immunized against Schistosoma mansoni, and provide the first physiologically relevant mechanism whereby the immune system might recognize and kill post-lung stage schistosomes.

Cutaneous sensitivity induced by immunization with irradiated Schistosoma mansoni cercariae. II. Autoimmunoregulation of cell-mediated cutaneous sensitivity and its reversal

C57BL/6 mice sensitized by abdominal, dermal exposure to irradiated (50 kR) Schistosoma mansoni cercariae develop partial protection against subsequent exposure with unattenuated cercariae and express cell-mediated cutaneous sensitivity upon challenge with irradiated cercariae. Autoimmunoregulation occurs as a part of this sensitization, and can be demonstrated by augmentation of cutaneous sensitivity upon use of appropriate regimens of cyclophosphamide. Mice exposed to irradiated cercariae by either intraperitoneal or ear pinna routes developed a transient hyporesponsiveness to cercarial challenge. This unresponsiveness was also reversed by pretreatment with cyclophosphamide. Timed removal of the site of effective sensitization (abdominal skin) 7 days after exposure consistently led to reduced cutaneous responsiveness. This artificially induced hyporesponsiveness was reversed by either cyclophosphamide treatment or systemic administration of anti-I-Jb, but not anti-I-Jk sera. The data indicate the involvement of cyclophosphamide-sensitive, I-J-bearing T-suppressor cells or factors in the autoimmunoregulation that controls this cutaneous sensitivity. Parallel challenge infection studies in immunized mice treated with cyclophosphamide demonstrated that the resultant augmentation of cutaneous sensitivity did not lead to concomitantly elevated levels of resistance. Furthermore, successful adoptive cell transfer of cutaneous responsiveness also did not ensure protection against cercarial challenge. These observations indicate that dermal cell-mediated anti-cercarial responsiveness is not a sufficient mechanism to explain resistance in mice immunized with irradiated cercariae.

Cutaneous sensitivity induced by immunization with irradiated Schistosoma mansoni cercariae. I. Induction, elicitation, and adoptive transfer analysis of cell-mediated cutaneous sensitivity

Exposure of C57BL/6 mice to highly irradiated (50 kR) cercariae of Schistosoma mansoni leads to the development of partial resistance against subsequent challenge with unattenuated cercariae. We have analyzed the cellular immune responses that occur during the afferent and efferent phases of this protective sensitization. Mice were immunized by exposure to irradiated S. mansoni cercariae. After challenge with irradiated cercariae, delayed-type (18-72 hr) cutaneous sensitivity reaction sites were rich in mononuclear cells and eosinophils. This reactivity was established by 4 days after sensitization, reached its maximum between 7 and 14 days after sensitization, and was maintained for over 20 weeks. These challenge reactions could be abrogated by treatment with either 200 mg/kg cyclophosphamide or 5 mg of hydrocortisone. Syngeneic adoptive transfer of cutaneous sensitivity was accomplished with lymphoid cells from the draining lymph nodes or spleens of mice sensitized 7-14 days previously. Negative selection studies of nylon-wool non-adherent cells from sensitized donors demonstrated that the cells responsible for transferring this eosinophil-rich, delayed-type cutaneous sensitivity to S. mansoni irradiated cercariae were Thy-1+, Lyt1+, Lyt2-, surface Ig- lymphocytes.

The role of pulmonary cellular reactions in the resistance of vaccinated mice to Schistosoma mansoni

A histopathological and ultrastructural study was made of schistosomula and associated inflammatory reactions in the lungs of normal mice, and mice previously vaccinated with irradiated cercariae. In normal mice at day 7 post-infection all schistosomula were located in blood vessels. From day 11 onwards an increasing proportion of schistosomula were intra-alveolar (80% from day 20). No cellular reactions were evident around intravascular parasites in normal mice but at later sampling times large compact foci were associated with alveolar parasites. Initial reactions, probably in response to non-specific tissue damage, were approximately 50% polymorphonuclear, and 50% mononuclear. Mononuclear cells predominated at later times. In spite of inflammation, no damage to the schistosomula was observed. There was no evidence for re-entry of schistosomula into blood vessels, and it was assumed entry into alveoli occurred accidentally as parasites attempted to traverse pulmonary blood vessels. The pattern of localization of schistosomula in vaccinated mice was similar to that in normal mice, the proportion in alveoli increasing with time (64% from day 20). The most significant difference was that intravascular schistosomula attracted foci of host leucocytes which were always 85% or more mononuclear, containing both lymphocytes and macrophages. The infiltrating cells enlarged the intersititium, separating the vascular endothelium from the alveolar epithelium. Fibrous protein was also deposited in the interstitial region. In some instances the complete blood-air barrier was destroyed by the infiltrates. Unusual paracrystalline inclusions were observed in alveolar macrophages and giant cells. The differences in cellular responses in vaccinated and normal mice suggest that challenge schistosomula stimulated an anamnestic immune response. The resulting inflammation, by impeding movement through the vasculature, terminated migration in the lungs, and accounted for the observed resistance to reinfection. The reactions in vaccinated mice have many of the features of a delayed hypersensitivity response implying that lung phase resistance in vaccinated mice may be T-cell rather than antibody-mediated.

Schistosoma mansoni: characterization of two protective monoclonal antibodies

Two monoclonal antibodies against the surface of S. mansoni schistosomula were found to confer significant passive protection to mice (M7B3A, range 28-70%; M22H12C, range 14-58%). No additive effect was observed when both were transferred together. Neither McAb bound to the cercarial surface but both bound to the surface of in vitro derived schistosomula and schistosomula recovered from mouse skin up to 3 days after infection. The McAbs were species specific, but not S. mansoni strain specific. M22H12C immunoprecipitated an 125I-labelled surface antigen of relative molecular weight (mol. wt) 32 000. In Western blotting of an NP40 schistosomular extract, M7B3A recognized an antigen smear of 13 000-18 000 with a dominant band at 16 000. This 16 000 antigen was recognized by serum from demonstrably immune mice and rats vaccinated with highly irradiated carcariae but not by sera from mice with chronic single sex or bisexual infections.

Patients at risk for AIDS-related opportunistic infections. Clinical manifestations and impaired gamma interferon production

We studied 81 men (79 homosexuals and 2 drug abusers) with persistent lymphadenopathy to determine whether those at risk for AIDS-related opportunistic infections could be identified prospectively. (Sixty-nine of 76 [91 per cent] had antibodies to human T-cell lymphotropic virus Type III [HTLV-III], and 76 of 79 [96 per cent] had abnormal T4/T8 cell ratios.) During the follow-up period (mean +/- S.E.M., 12.9 +/- 0.5 months; range, 8 to 19), infections developed in none of 38 patients with lymphadenopathy alone and in only 1 of 15 (7 per cent) with antecedent herpes zoster infection; however, 13 of 28 (46 per cent) with lymphadenopathy accompanied by constitutional symptoms or oral candidiasis or both had opportunistic infections within the follow-up period. Among the results of various T-cell assays, only antigen-stimulated lymphocyte proliferation and gamma interferon generation, which were absent or barely measurable in those in whom AIDS ultimately developed, were of prognostic value. T cells from 15 patients, 11 of whom had constitutional symptoms or thrush, failed to generate antigen-induced gamma interferon; infections developed in 10 of these 15 (67 per cent) within a mean of 8.2 months. These results suggest that patients with AIDS-related complex who are at risk for opportunistic infections within a year can be identified by correlating clinical manifestations with antigen-stimulated T-cell responses--in particular, with the production of gamma interferon.

Production of and in vitro response to interleukin 2 in the acquired immunodeficiency syndrome

To test the hypothesis that deficient interleukin 2 (IL-2) secretion may underlie the impaired capacity of T cells from patients with Acquired Immunodeficiency Syndrome (AIDS) and the AIDS-related complex (ARC) to generate the macrophage-activating lymphokine, gamma interferon (IFN-gamma), we used five specific microbial antigens to examine IL-2 production. Mononuclear cells from only one of 32 (3%) AIDS patients secreted normal levels of IL-2, and 21 (66%) failed to produce any detectable IL-2. For 36 ARC patients, IL-2 generation was normal in nine (25%) and absent in 11 (31%). Given these results, recombinant (r) IL-2 was tested for its capacity to stimulate or enhance IFN-gamma production. rIL-2 (10 U/ml) alone stimulated cells from controls, ARC, and AIDS patients to secrete 93 +/- 25, 99 +/- 33, and 7 +/- 3 U/ml of IFN-gamma, respectively. rIL 2 (10 U/ml) plus antigen induced no change in mean IFN-gamma levels for controls, a 4.4-fold increase for 17 AIDS patients (16 +/- 16 vs. 71 +/- 21 U/ml), and a 7.2-fold increase (18 +/- 5 vs. 130 +/- 27 U/ml) for 19 ARC patients with abnormal IFN-gamma generation to antigen alone. Individual responses indicated that six of the 17 (35%) AIDS patients with opportunistic infections and 12 of the 19 (63%) with ARC were apparent responders to 10-100 U/ml of rIL-2. These results (a) document profound impairment in antigen-induced IL-2 secretion by AIDS and ARC T cells, (b) indicate that, in vitro, mononuclear cells from certain patients can respond to rIL-2 with enhanced IFN-gamma production, and thus (c) suggest that in selected patients rIL-2 might have a potentially beneficial therapeutic (AIDS) or prophylactic (ARC) effect against opportunistic infections.

Schistosoma mansoni: challenge attrition during the lung phase of migration in vaccinated and serum-protected rats

Serum harvested from Sprague-Dawley rats twice vaccinated with gamma-irradiated cercariae of Schistosoma mansoni is able to protect naive recipients against a challenge infection, but the challenge parasites are susceptible to immune elimination over a very short period of time. Thus, vaccinated rat serum protects recipients against a percutaneous cercarial challenge when transferred on Day +5 but not Day 0 and protects recipients against a tail vein challenge with 5-day-old lung worms when transferred on Days 0 or +1, but not Days +4 or +5. Rats challenged with lung worms via the tail vein and given serum on Day +3 exhibit approximately half the protection expressed by counterparts that received serum on Day 0. However, vaccinated rat serum does not protect naive recipients against a lung worm challenge introduced directly into the liver. These data indicate that immune elimination of challenge parasites in the vaccinated rat model is site-dependent rather than stage-dependent, and most probably occurs during the lung phase of parasite migration.

Vaccination against Schistosoma mansoni with purified surface antigens

Two surface antigens were isolated from young or adult schistosomes by affinity chromatography with monoclonal antibodies. Vaccination with an antigen having a molecular weight of 155,000 gave partial protection against challenge in some batches of mice and in a group of cynomolgus monkeys. Vaccination with an antigen having a molecular weight of 53,000 gave similar levels of protection in mice. The results demonstrate that protection can be obtained with single antigens, but the precise requirements for reproducible vaccination are as yet unknown.

Macrophages as effector cells in immunity to malaria

Experiments with malaria in mice suggest that protective immunity depends not only on antibody but also on activation of macrophages. Activated macrophages may cause intra-erythrocytic death of parasites by releasing reactive oxygen intermediates and/or tumour necrosis factor. Macrophage activation for both types of product correlates well with the timing of recovery in a range of different malaria infections and in mice protected by vaccination.