Cercarial Dermatitis Caused by Bird Schistosomes Comprises Both Immediate and Late Phase Cutaneous Hypersensitivity Reactions

Avian schistosomes are the primary causative agent of cercarial dermatitis in humans, but despite its worldwide occurrence, little is known of the immune mechanism of this disease. Using a murine model, hosts were exposed to primary (1x) and multiple (4x) infections of Trichobilharzia regenti via the pinna. Penetration of larvae into the skin evoked immediate edema, thickening of the exposure site, and an influx of leukocytes, including neutrophils, macrophages, CD4+ lymphocytes, and mast cells. A large proportion of the latter were in the process of degranulating. After 1x infection, inflammation was accompanied by the release of IL-1beta, IL-6, and IL-12p40. In contrast, in 4x reinfected animals the production of histamine, IL-4, and IL-10 was dramatically elevated within 1 h of infection. Analysis of Ag-stimulated lymphocytes from the skin-draining lymph nodes revealed that cells from 1x infected mice produced a mixed Th1/Th2 cytokine response, including abundant IFN-gamma, whereas cells from 4x reinfected mice were Th2 polarized, dominated by IL-4 and IL-5. Serum Abs confirmed this polarization, with elevated levels of IgG1 and IgE after multiple infections. Infection with radiolabeled cercariae revealed that almost 90% of larvae remained in the skin, and the majority died within 8 days after infection, although parasites were cleared more rapidly in 4x reinfected mice. Our results are the first demonstration that cercarial dermatitis, caused by bird schistosomes, is characterized by an early type I hypersensitivity reaction and a late phase of cutaneous inflammation, both associated with a polarized Th2-type acquired immune response.

IL-4 receptor signaling is required for mannose receptor expression by macrophages recruited to granulomata but not resident cells in mice infected with Schistosoma mansoni

High levels of mannose receptor (MR) expression and pinocytic activity are a hallmark of Th2 cytokine-driven alternative MPhi activation in vitro. We examined expression of MR in situ and its regulation by Th1/Th2 cytokines in IL-4Ralpha -/- and wild-type (WT) mice challenged with Schistosoma mansoni. Parasite eggs induce a vigorous granulomatous response, driven by Th2 cytokines in WT mice, but by Th1 cytokines in IL-4Ralpha -/- mice. MR was expressed by granuloma MPhi in WT mice but not in IL-4Ralpha -/- mice, whose MPhi nevertheless exhibited a mature phenotype and morphology. By contrast expression of MR in resident tissue MPhi and endothelial cells appeared unaffected by Th1/Th2 cytokines. Our results revealed that Th1/Th2 cytokines differentially regulate MR according to cell type and play a critical role in regulating MR expression by MPhi recruited to granulomata. We also present evidence that components of schistosome eggs and a fraction of their secretions are ligands of MR, and suggest that MR activity may be of functional significance in the granulomatous response.

Interleukin-12 p40 secretion by cutaneous CD11c+ and F4/80+ cells is a major feature of the innate immune response in mice that develop Th1-mediated protective immunity to Schistosoma mansoni

Radiation-attenuated (RA) schistosome larvae are potent stimulators of innate immune responses at the skin site of exposure (pinna) that are likely to be important factors in the development of Th1-mediated protective immunity. In addition to causing an influx of neutrophils, macrophages, and dendritic cells (DCs) into the dermis, RA larvae induced a cascade of chemokine and cytokine secretion following in vitro culture of pinna biopsy samples. While macrophage inflammatory protein 1alpha and interleukin-1beta (IL-1beta) were produced transiently within the first few days, the Th1-promoting cytokines IL-12 and IL-18 were secreted at high levels until at least day 14. Assay of C3H/HeJ mice confirmed that IL-12 secretion was not due to lipopolysaccharide contaminants binding Toll-like receptor 4. Significantly, IL-12 p40 secretion was sustained in pinnae from vaccinated mice but not in those from nonprotected infected mice. In contrast, IL-10 was produced from both vaccinated and infected mice. This cytokine regulates IL-12-associated dermal inflammation, since in vaccinated IL-10(-/-) mice, pinna thickness was greatly increased concurrent with elevated levels of IL-12 p40. A significant number of IL-12 p40(+) cells were detected as emigrants from in vitro-cultured pinnae, and most were within a population of rare large granular cells that were Ia(+), consistent with their being antigen-presenting cells. Labeling of IL-12(+) cells for CD11c, CD205, CD8alpha, CD11b, and F4/80 indicated that the majority were myeloid DCs, although a proportion were CD11c(-) F4/80(+), suggesting that macrophages were an additional source of IL-12 in the skin.

Signaling via interleukin-4 receptor alpha chain is required for successful vaccination against schistosomiasis in BALB/c mice

Although protective immunity in C57BL/6 mice induced by a single dose of the radiation-attenuated schistosome vaccine is believed to be mediated by Th1-type immune responses, we here report that in BALB/c mice protection can also depend upon signaling via the interleukin-4 (IL-4) receptor which conventionally governs the development of Th2-type immune responses. We show that in BALB/c mice deficient for the IL-4 receptor alpha chain (IL-4Ralpha(-/-)), which are unresponsive to IL-4 and IL-13, vaccine-induced protection is abrogated compared with that in wild-type (WT) mice. In vaccinated IL-4Ralpha(-/-) mice, IL-12p40 production by cells from the skin exposure site was elevated, although gamma interferon (IFN-gamma) production in draining lymphoid tissues was similar in WT and IL-4Ralpha(-/-) mice. Nevertheless, the effector response in IL-4Ralpha(-/-) mice was Th1 biased with elevated IFN-gamma in the lungs and higher immunoglobulin G2a (IgG2a) and IgG2b titers but negligible quantities of Th2-associated IgG1 and IgE. Interestingly, levels of IL-4 were equivalent in WT and IL-4Ralpha(-/-) mice, indicating that Th2 responses were not dependent upon signaling by IL-4 or IL-13. No differences in the phenotype and composition of the pulmonary effector mechanism that might explain the failure to induce protection in IL-4Ralpha(-/-) mice were detected. However, passive transfer of partial protection to naive IL-4Ralpha(-/-) mice, using serum from vaccinated WT mice, indicates that Th2-associated antibodies such as IgG1 have a role in parasite elimination in BALB/c strain mice and that signaling via IL-4R can be an important factor in the generation of protection.

Characterization, cloning and immunogenicity of antigens released by transforming cercariae of Schistosoma mansoni

A schistosome infection is initiated when the parasite penetrates the skin of a susceptible host. Relatively large quantities of protein are released by transforming cercariae compared to later larval stages. This represents the first parasite material to which the host's immune system is exposed, yet little is known about the proteins which are released during the first few hours post-transformation. We have shown that antiserum raised against such molecules was capable of imparting protection against a schistosome challenge infection upon passive transfer to naïve mice. By screening a cercarial cDNA library with this serum, 38 positive clones were identified. Sequence analysis showed these to represent 8 different molecules which included Schistosoma mansoni 21-7 kDa antigen, calcium-binding-protein and the vaccine candidate glutathione S-transferase (Sm28GST). In addition, 5 clones were isolated, 1 of which had significant homology to many cytochrome C proteins, another with leukocyte elastase inhibitors and 3 which represented novel molecules. Four clones were expressed in a prokaryotic high-level expression vector, sera produced against each purified recombinant protein and used subsequently to probe Western blots and parasite sections. The leukocyte elastase inhibitor homologue and 2 unknowns induced significant proliferation by lymph node cells recovered from mice vaccinated with irradiated cercariae. More strikingly, the 2 novel proteins stimulated very high levels of interferon gamma (IFNgamma) secretion both by lymph node cells and those recovered by broncho-alveolar lavage from the lungs of vaccinated mice. Such results will be discussed in the context of vaccine development.

IL-18 potentiates the adjuvant properties of IL-12 in the induction of a strong Th1 type immune response against a recombinant antigen

Due to the synergistic effects of IL-12 and IL-18, and to their importance in establishing a Th1 type immune response, we investigated the potential of a combined administration of both cytokines as an adjuvant for recombinant antigens. As a model system, we used a schistosome T cell antigen recently identified in our group. By co-adsorption of this antigen on alum in the presence of IL-12 and IL-18, we demonstrate that IL-18 enhances the effects of IL-12 in inducing an antigen-specific Th1 type CD4(+) T cell response as well as high titres of IgG1, IgG2a, and IgG2b antibodies.

Interleukin-12 can directly induce T-helper 1 responses in interferon-gamma (IFN-gamma) receptor-deficient mice, but requires IFN-gamma signalling to downregulate T-helper 2 responses

An in vivo model of pulmonary granuloma formation around embolized schistosome eggs was investigated as an environment in which to analyse a role for interleukin-12 (IL-12) in the differentiation of T-helper 1 (Th1) and Th2 subsets. Specifically, mice deficient for the interferon-gamma receptor (IFN-gammaR-/-) were used to determine the role for IL-12 in the absence of IFN-gamma-mediated signalling. We show that recombinant IL-12 administered to IFN-gammaR-/- mice caused the up-regulation of mRNA for IFN-gamma in lung tissue, and the secretion of abundant IFN-gamma by in vitro-cultured lymph node cells in response to egg antigens. This indicates that IL-12 can act independently of IFN-gamma to induce the development of Th1 cells. Administration of rIL-12 to wild-type mice markedly reduced the secretion of Th2-associated cytokines, IL-4 and IL-5. However, these cytokines were not dramatically reduced in IFN-gammaR-/- mice treated with IL-12. We conclude that inhibition of these cytokines by IL-12 is primarily dependent upon effective IFN-gamma signalling, although abrogation of T-cell derived IL-10 appeared to be dependent upon IL-12. We also show that increases in mRNA for the beta2 subunit of the IL-12 receptor and the p40 subunit of IL-12 after rIL-12 treatment were lower in IFN-gammaR-/- mice, compared to wild-type mice, indicating that their expression was primarily dependent upon IFN-gamma with only a minor role for IL-12.

Isolation of T-cell antigens by using a recombinant protein library and its application to the identification of novel vaccine candidates against schistosomiasis

We present here a novel approach to identify T-cell antigens from any infectious agent by use of a library of purified recombinant proteins. Essential features of this strategy include (i) a highly efficient cDNA cloning system which negatively selects against nonrecombinant transformants by making use of the bacterial EcoK restriction system, (ii) affinity staining of cDNA clones expressing recombinant proteins, and (iii) a procedure of simultaneous purification of recombinant proteins from large numbers of isolated clones (representing the protein library) in a single step from pools consisting of up to 24 individual clones. The feasibility of the screening system was confirmed by constructing a protein library of the human parasite Schistosoma mansoni. The recombinant antigens of this library were used to stimulate CD4(+) T cells derived from the axillary lymph nodes of mice vaccinated with irradiated cercariae. In initial screening experiments, we detected parasite-specific proliferation and gamma interferon (IFN-gamma) secretion in response to several pools of cDNA clones. Further analysis of one particular pool revealed that only one of its constituents stimulated considerable IFN-gamma secretion by CD4(+) T cells and that the expressed antigen is identical to a small fragment of myosin heavy chain.

Formation of multinucleated giant cells in the mouse lung is promoted in the absence of interleukin-12

The formation of multinucleated giant cells (MGCs) in an in vivo model of pulmonary inflammation was investigated to determine whether these cells are the result of a dominant T helper (Th) 1 or Th2 cytokine environment. We report that knockout (KO) mice with a disrupted interleukin (IL)-12 p40 gene exposed to the helminth Schistosoma mansoni had abundant and very large MGCs (> 50 microm) in their lungs concurrent with extensive eosinophilia and a population of large macrophages. Many of the MGCs and macrophages appeared to have phagocytosed eosinophils as part of a clearance process. The KO mice also had a strongly polarized Th2 immune response as judged by elevated levels in the lungs of messenger RNA (mRNA) transcripts for IL-4, IL-5, IL-6, and IL-13, but decreased levels of mRNA for interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). In addition, cells recovered by bronchoalveolar lavage from the airways of these mice secreted a Th2-biased profile of cytokines upon restimulation in vitro with parasite antigen. In contrast, wild-type C57BL/6 or KO mice treated with recombinant IL-12 had a polarized Th1 phenotype with elevated levels of IFN-gamma and TNF-alpha mRNA in the lungs, and an airway cell population that secreted abundant IFN-gamma. Very few MGCs were detected in these mice, and there was an absence of pulmonary eosinophilia. We conclude that the formation of MGCs in our model is promoted in the absence of IL-12 and is linked instead to the abundance of Th2 cytokines, notably IL-4 and IL-13.

The radiation-attenuated schistosome vaccine induces high levels of protective immunity in the absence of B cells

Radiation-attenuated cercariae of Schistosoma mansoni elicit consistently high levels of protective immunity in mice. The cell-mediated pulmonary effector mechanisms have been well characterized but the role of B cells and antibodies remains ill defined. We have compared the immune responses of B-cell-deficient (muMT) mice and their wild-type (WT) counterparts following exposure to the attenuated vaccine. Both groups mounted a T helper type 1 (Th1)-biased response in the skin-draining lymph nodes after vaccination. Interferon-gamma was the dominant cytokine secreted by airway leucocytes after challenge in both muMT and WT mice, but there was a somewhat greater Th2 component in the former animals. The cellular infiltrates observed in the airways, and the pulmonary effector foci, were of similar composition in the two groups although some large foci were present in the muMT mice. There was a marked dichotomy in the protection induced in muMT animals by a single vaccination, with two-thirds showing levels similar to their WT counterparts, demonstrating that cell-mediated mechanisms alone can provide adequate protection. The remaining muMT mice had a mean worm burden identical to that of their challenge controls. A possible explanation is that a proportion of the muMT animals have a genetic defect closely associated with the mu-heavy-chain locus on chromosome 12, which affects their ability to mount a protective cell-mediated response. Three vaccinations enhanced the immunity of WT animals, most likely by augmenting antibody-mediated mechanisms. In contrast, no enhancement was seen in muMT mice, suggesting that the cell-mediated response is not boosted by multiple exposures to attenuated larvae.

Immune responses to the radiation-attenuated schistosome vaccine: what can we learn from knock-out mice?

The goal of an effective schistosomiasis vaccine has proved elusive but the protective immunity induced in mice by radiation-attenuated cercaria larvae provides an appropriate model from which such a vaccine might be developed. Using gene-disrupted mice, we have analysed the process of immune priming by attenuated larvae of Schistosoma mansoni and the nature of the pulmonary effector response directed against a challenge infection. Vaccination stimulates expansion of IFNgamma-producing T-helper cells in the skin-draining lymph nodes. IL-12 is crucial in determining the Thl direction of this initial response but the cells of origin and the parasite components which stimulate its production are unknown. In the effector response, focal aggregates comprising mainly mononuclear cells accumulate around challenge larvae in the lungs, a process orchestrated by IFNgamma. This cytokine up-regulates nitric oxide synthase activity but we were unable to implicate nitric oxide as a cytotoxic agent causing challenge parasite elimination. An alternative action for IFNgamma may be to up-regulate adhesion molecule expression, increasing the cohesiveness of effector foci the better to block parasite migration, but the adhesive interactions so far examined do not appear relevant. In contrast, TNF induction is essential to protection, and we are currently testing the hypothesis that it determines the speed of the effector response following arrival of challenge larvae in the lungs.

Interleukin-12 and the host response to parasitic helminths; the paradoxical effect on protective immunity and immunopathology

In general, helminth infections are associated with the development of dominant Th2-mediated immune responses which may be host protective but can also be the cause of immunopathology. Interleukin 12 (IL-12) is known to be a potent inhibitor of Th2 immune responses and as such it might be expected to have an important modulatory role in helminth-induced immune responses. In this review, we discuss the effect of IL-12 on susceptibility to infection, protective immunity and immunopathology, in the context of exposure to a range of helminths including intestinal nematodes, filariae and schistosomes. It is apparent that the effects of IL-12 are complex and can be beneficial as well as detrimental for the host. The precise role of IL-12 depends upon a number of factors including the type of helminth and the specific tissue involved in the inflammatory response.

In the absence of IL-12, the induction of Th1-mediated protective immunity by the attenuated schistosome vaccine is impaired, revealing an alternative pathway with Th2-type characteristics

Vaccination of mice with irradiated Schistosoma mansoni larvae confers high levels of immunity which is mediated by Th1-type lymphocytes. To investigate a possible role for IL-12 in the induction of protection, we have compared the immune response of IL-12 p40-deficient (KO) mice and their C57BL/6 (WT) counterparts following vaccination. Cultured lymph node cells from KO mice had markedly altered cytokine profiles with significantly decreased production of IFN-gamma increased IL-4. Correspondingly, KO mice had enhanced levels of IgE. After challenge, cells recovered from the lungs of KO mice secreted abundant IL-4 and IL-5 but little IFN-gamma, while flow cytometric and histological analysis of lung cell populations recorded a very high proportion of eosinophils. The levels of protection in KO mice were substantially lower than in their WT counterparts, demonstrating the importance of IL-12 and Th1-mediated immune responses. This conclusion is reinforced by the administration of rIL-12 to KO mice immediately after vaccination which led to increased IFN-gamma and the restoration of protective immunity. Nevertheless, the data also indicated that the limited levels of protection induced in KO mice occur via an IL-12-independent pathway, possibly mediated by Th2 cells.

Vaccination against Schistosomiasis: The case for Lung-stage Antigens

The development of an effective vaccine against human schistosomiasis remains a highly desirable yet elusive goal. In this article, Adrian Mountford and Richard Harrop focus attention on an approach that aims to identify proteins from Schistosoma mansoni that are capable of stimulating protective Th1 cell-mediated immune responses. They propose that the most likely source of such antigens is the lung-stage schistosomulum.

Interleukin-12 and protective immunity to schistosomes

The attenuated vaccine against Schistosoma mansoni induces Th1-mediated protective immunity and we have sought to identify a role for IL-12 in this model. Elevated levels of IL-12 (p40 mRNA) were detected in the lymph nodes (LN) and the lungs of vaccinated mice, whilst treatment of vaccinated mice with anti-IL-12 antibodies decreased the ratio of IFN gamma:IL-4 secreted by in vitro-cultured LN cells. However, there was only marginal abrogation of the level of resistance in these mice. Soluble antigens from the lung-stage of the parasite (SLAP) appeared to be efficient stimulators of IFN gamma and IL-12 secretion. These antigens when used to immunise mice in conjunction with IL-12 as an adjuvant, elicited a polarised Th1 response with abundant IFN gamma secretion but no IL-4. This immunisation regime also induced significant protection against reinfection, whereas inoculation of mice with SLAP alone did not. The induction of a dominant Th1 response using SLAP + IL-12 probably operates via IFN gamma production by natural killer (NK) cells stimulated by IL-12, since in vivo ablation of NK cells using anti-NK1.1 antibody reduced CD4(+)-dependent IFN gamma production from cultured LN cells by over 97%. Nevertheless, in mice with a genetic disruption of the IFN gamma receptor, administration of SLAP + IL-12 induced levels of IFN gamma equal to those in wild-type mice, thus showing that in this model IL-12 can directly prime T cells independent of IFN gamma. Clearly, IL-12 has a critical role in protective immunity to schistosomes and it may aid the development of an effective vaccine against this disease.

Induction of Th1 cell-mediated protective immunity to Schistosoma mansoni by co-administration of larval antigens and IL-12 as an adjuvant

In this study, rIL-12, which is a powerful inducer of Th1 lymphocyte development, was administered to mice as an adjuvant in conjunction with a soluble lung-stage Ag preparation (SLAP) derived from lung-stage larvae of Schistosoma mansoni to potentiate Th1-mediated immune responses and induce resistance to reinfection. Immunization of mice with one or two doses of SLAP + IL-12 elicited a dominant population of Ag-specific Th1 lymphocytes in the draining lymph nodes, as judged by the secretion of abundant IFN-gamma but undetectable levels of IL-4, upon antigenic restimulation in vitro. In contrast, SLAP alone induced a mixed population of Th1 and Th2 cells with secretion of IFN-gamma, IL-4, and IL-10. The development of a biased Th1 cell population in mice immunized with SLAP + IL-12 was reflected in enhanced levels of Ag-specific IgG2a but decreased levels of IgG1 and total IgE serum Abs. Ablation of NK1.1+ cells before the administration of a single dose of SLAP + IL-12 reduced Th cell proliferation and almost completely inhibited secretion of IFN-gamma by in vitro-cultured lymph node cells. This indicates that NK cells stimulated by IL-12 shortly after vaccination are critical to the subsequent development of Ag-specific Th1 cells. Finally, it is demonstrated that the delivery of two doses of SLAP + IL-12 to mice is sufficient to elicit moderate but highly significant levels of protective immunity against challenge infection.

Induction of Th1 cell-mediated protective immunity to Schistosoma mansoni by co-administration of larval antigens and IL-12 as an adjuvant

In this study, rIL-12, which is a powerful inducer of Th1 lymphocyte development, was administered to mice as an adjuvant in conjunction with a soluble lung-stage Ag preparation (SLAP) derived from lung-stage larvae of Schistosoma mansoni to potentiate Th1-mediated immune responses and induce resistance to reinfection. Immunization of mice with one or two doses of SLAP + IL-12 elicited a dominant population of Ag-specific Th1 lymphocytes in the draining lymph nodes, as judged by the secretion of abundant IFN-gamma but undetectable levels of IL-4, upon antigenic restimulation in vitro. In contrast, SLAP alone induced a mixed population of Th1 and Th2 cells with secretion of IFN-gamma, IL-4, and IL-10. The development of a biased Th1 cell population in mice immunized with SLAP + IL-12 was reflected in enhanced levels of Ag-specific IgG2a but decreased levels of IgG1 and total IgE serum Abs. Ablation of NK1.1+ cells before the administration of a single dose of SLAP + IL-12 reduced Th cell proliferation and almost completely inhibited secretion of IFN-gamma by in vitro-cultured lymph node cells. This indicates that NK cells stimulated by IL-12 shortly after vaccination are critical to the subsequent development of Ag-specific Th1 cells. Finally, it is demonstrated that the delivery of two doses of SLAP + IL-12 to mice is sufficient to elicit moderate but highly significant levels of protective immunity against challenge infection.

Antigens derived from lung-stage larvae of Schistosoma mansoni are efficient stimulators of proliferation and gamma interferon secretion by lymphocytes from mice vaccinated with attenuated larvae

Protective immunity in C57BL/6 mice exposed to optimally irradiated larvae of Schistosoma mansoni operates against challenge parasites in the lungs and is dependent upon T-helper 1 (Th1) lymphocytes which secrete abundant gamma interferon (IFN-gamma). As an initial step in the identification of the molecules which mediate this immunity, antigenic materials released by larvae at various times during in vitro culture were compared for the ability to induce proliferation of lymph node cells recovered from mice 4 to 6 days after exposure to attenuated parasites. Cells from mice vaccinated with cercariae proliferated most strongly to larval antigens released soon after transformation. In contrast, cells from mice immunized with lung-stage schistosomula responded poorly to these early secretions but proliferated vigorously to antigens released by older larvae. In further studies on the cytokine profile of the responding lymphocytes, it was observed that the balance between IFN-gamma and interleukin-4 (IL-4) secretion depended on the source of antigen used for restimulation. Thus, material released between days 6 and 8 by in vitro-cultured larvae, and the soluble extracts of whole lung-stage larvae, induced abundant IFN-gamma but little IL-4. This finding implies that an overwhelming proportion of the lymphocytes responsive to lung-stage antigens had the Th1 phenotype. In contrast, antigens from cercariae and skin-stage larvae induced the lowest levels of IFN-gamma but higher levels of IL-4. It appears that a proportion of the cells with specificities for early antigens had the Th2 or Th0 phenotype. Our results emphasize that antigens from lung-stage larvae are an important source of potentially protective molecules.

The profile of IgG1 and IgG2a antibody responses in mice exposed to Schistosoma mansoni

The segregation of IgG2a and IgG1 immunoglobulin isotypes as markers for Th1 and Th2 lymphocytes respectively, was investigated in mice exposed to normal or optimally-irradiated S. mansoni cercariae. Using a panel of ELISAs, soluble antigens from lung-stage schistosomula, adult worms, or eggs, were probed with serum samples collected at biweekly intervals. Infected mice developed increased IgG1 responsiveness to all three antigens, especially between weeks five and seven, whereas IgG2a responses were lower, particularly to egg antigens. This confirms that Th2 responses are dominant after the onset of patency in infected mice. In comparison, vaccinated mice developed lower levels of IgG1, and higher levels of IgG2a to larval and worm antigens. Thus, they had balanced expression of IgG1 and IgG2a, despite having a dominant Th1 lymphocyte population. An elevated IgG1 response to egg antigens in vaccinated mice challenged with normal parasites, occurred two weeks later than in normal mice. Mice exposed to male-only cercariae developed IgG1 and IgG2a antibodies to larval and worm antigens. However, they also had elevated IgG1 to egg antigens from week five, despite a total absence of eggs. Therefore, adult worm antigens may cross react with the egg and stimulate the switch to Th2 dominated responsiveness.

Fractionation of schistosome antigens by high performance electrophoretic chromatography and their screening for the ability to induce Th1 lymphocyte activity

The technique of high performance electrophoretic chromatography (HPEC) has been used to fractionate soluble antigens from adult Schistosoma mansoni worms on the basis of molecular weight (MW), prior to screening for their ability to stimulate T lymphocyte activity. Approximately 250 micrograms of protein were separated by continuous electrophoresis through an SDS polyacrylamide gel into 30-50 aqueous samples of minimal volume (80 microliters). Each consecutive sample contained a limited number of proteins of progressively greater MW, although the resolution of the fractionation was affected by a number of factors including acrylamide concentration, gel length, gel diameter and electrophoretic current. Following the extraction of SDS using Calbiosorb resin, the aqueous fractions were used directly to stimulate cultures of lymphocytes taken from the lymph nodes of infected or vaccinated mice. The most promising fractions were those containing proteins which induced the release of high levels of interferon-gamma relative to the extent of proliferation. This suggests that these proteins are good inducers of Th1 lymphocyte activity.

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.

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.

The generation of interferon-gamma-producing T lymphocytes in skin-draining lymph nodes, and their recruitment to the lungs, is associated with protective immunity to Schistosoma mansoni

We have examined immunological responses in the skin-draining lymph nodes (SLN) and lungs of mice during the 3 weeks after percutaneous exposure to attenuated larvae of Schistosoma mansoni. Cercariae irradiated with 20 krads (V20) were highly protective and sustained an increased number of CD4+ T cells in the SLN. On secondary exposure to schistosome antigen in vitro, these cells were capable of proliferating and secreting high levels of interferon-gamma (IFN-gamma) and interleukin-3 (IL-3). However, in mice exposed to non-protective 80 krad-irradiated (V80) cercariae, secretion of these cytokines occurred early and only transiently. Significantly elevated numbers of CD4+ T lymphocytes were recoverable on Day 21 from the lungs of V20, but not V80 mice. These cells secreted high levels of IFN-gamma and IL-3 in vitro, but not IL-2 and IL-4. Mice immunized intravenously with attenuated lung-stage schistosomula were not protected, despite having an elevated pulmonary lymphocyte population. Moreover these cells failed to secrete IFN-gamma and IL-3. However, significant protection was achieved where exposure of mice to a combination of V80 cercariae and lung-stage schistosomula resulted in the recruitment of IFN-gamma secreting cells to the lungs. We conclude that the success of the irradiated vaccine depends not only on the generation of a population of antigen-specific T-helper cells in the SLN, but also recruitment of these cells to the lungs before challenge.

Patterns of cytokine production and proliferation by T lymphocytes differ in mice vaccinated or infected with Schistosoma mansoni

C57BL/6 mice vaccinated with irradiated cercariae of Schistosoma mansoni are highly resistant to challenge infection. To examine the role of T-helper (Th) activity in these vaccinated (V20) mice, cells from skin- and lung-draining lymph nodes (LN) and the spleen were cultured in vitro with soluble schistosomular antigen. Peak proliferation and release of T-cell growth factor (TCGF) by axillary LN cells on Day 5, and by mediastinal LN cells on Day 18, reflected the kinetics of parasite migration. High levels of interferon-gamma (IFN-gamma) were detected and production was prolonged, particularly in the mediastinal LN. The majority of the above activity was ablated with anti-CD4 antibody. IFN-gamma production by spleen cells increased, whilst proliferation and TCGF release remained low. Although levels of proliferation were similar, more IFN-gamma was released by LN cells from V20 mice than by those from mice infected with normal parasites (NI). This difference in IFN-gamma production was magnified by the greater number of cells in LN of V20 than NI mice. On Day 22 post-exposure, 24-fold more IFN-gamma was produced per pair of axillary LN in the former group. LN cells from V20 mice produced interleukin (IL)-2 and IL-4, whereas those from NI mice released IL-2 but negligible IL-4. Greater quantities of IL-3 were secreted by cells from V20 than from NI mice. These results support the conclusion that IFN-gamma-producing memory Th cells, generated in the LN of V20 mice, play an important role in protective immunity against S. mansoni.