An IL-12-based vaccination method for preventing fibrosis induced by schistosome infection

IL-10 and the dangers of immune polarization: excessive type 1 and type 2 cytokine responses induce distinct forms of lethal immunopathology in murine schistosomiasis

To dissect the controversial roles of type 1 and type 2 cytokines to the pathogenesis of schistosomiasis, we generated IL-10/IL-4- and IL-10/IL-12-deficient mice that develop highly polarized type 1 and type 2 cytokine responses, respectively. Interestingly, the Th1-polarized IL-10/IL-4-deficient mice rapidly lost weight at the onset of egg-laying and displayed 100% mortality by wk 9 postinfection. This acute mortality was linked to overexpression of the proinflammatory mediators IFN-gamma, TNF-alpha, and inducible NO and the formation of nonfibrotic granulomas. Elevated serum aspartate transaminase levels confirmed that mortality was in part attributable to acute hepatotoxicity. In contrast, the Th2-polarized IL-10/IL-12-deficient mice developed a progressive wasting disease that correlated with increased hepatic fibrosis, formation of large eosinophil-rich granulomas, a 10-fold increase in IL-4 and IL-13, and significant mortality during the chronic stages of infection. Surprisingly, IL-10-deficient mice displayed pathological features that were characteristic of both extremes, while wild-type mice developed relatively successful long term chronic infections. These data demonstrate that IL-10 significantly suppresses type 1 and type 2 cytokine development in IL-4- and IL-12-deficient mice, respectively, thereby impeding the development of severe egg-induced pathology in the single cytokine-deficient animals. Together, these findings reveal the central regulatory role of IL-10 in the pathogenesis of schistosomiasis and illustrate that excessive type 1 and type 2 cytokine responses trigger distinct, but equally detrimental, forms of pathology following infection.

The potential for vaccine development against chlamydial infection and disease

Chlamydia trachomatis and Chlamydia pneumoniae appear to share a common immunobiology with about 80% of their protein coding genes being orthologs. Progress in DNA vaccine development for C. trachomatis suggests that such a subunit approach may prove useful for C. pneumoniae. The recent finding that it is possible to select for chlamydiae with targeted mutations in key metabolic genes together with the new knowledge of the chlamydia genome also suggests that it may be possible to develop live attenuated strains of chlamydiae for use as vaccine.

Repeated exposure induces periportal fibrosis in Schistosoma mansoni-infected baboons: role of TGF-beta and IL-4

Recently, we observed that repeated Schistosoma mansoni infection and treatment boost Th2-associated cytokines and TGF-beta production in baboons. Other studies have shown that some chronically infected baboons develop hepatic fibrosis. Because TGF-beta, IL-2, and IL-4 have been shown to participate in development of fibrosis in murine schistosomiasis, the present study examined whether repeated exposure stimulates hepatic fibrosis in olive baboons. To test this hypothesis, animals were exposed to similar numbers of S. mansoni cercariae given once or repeatedly. After 19 wk of infection, animals were cured with praziquantel and reinfected once or multiple times. Hepatic granulomatous inflammation and fibrosis were assessed from serial liver biopsies taken at weeks 6, 9, and 16 after reinfection and egg Ag (schistosome egg Ag)-specific cytokine production by PBMC were measured simultaneously. Periportal fibroblast infiltration and extracellular matrix deposition (fibrosis), angiogenesis, and biliary duct hyperplasia developed in some animals. The presence and amount of fibrosis directly correlated with the frequency of exposure. Fibrosis was not associated with adult worm or tissue egg burden. The amount of fibrosis correlated with increased schistosome egg Ag-driven TGF-beta at 6, 9, and 16 wk postinfection (rs = 0.9, 0.8, and 0.54, respectively, all p < 0.01) and IL-4 production (p = 0.02) at 16 wk postinfection and not IFN-gamma, IL-2, IL-5, or IL-10. These data suggest that repeated exposure is a risk factor for periportal fibrosis by a mechanism that primes lymphocytes to produce increased levels of profibrotic molecules that include TGF-beta and IL-4.

Single cell analysis reveals that IL-4 receptor/Stat6 signaling is not required for the in vivo or in vitro development of CD4+ lymphocytes with a Th2 cytokine profile

The concept that IL-4 is the primary signal for Th2 lymphocyte differentiation has recently been put in doubt by studies in which the production of Th2-associated cytokines was detected in mice deficient in IL-4 synthesis or IL-4R triggering. In this study, we formally demonstrate by single cell analysis that CD4+ lymphocytes with a classical Th2 phenotype (IL-4+, IL-5+, IFN-gamma-, IL-2-) develop in significant numbers in helminth-infected mice deficient in either IL-4R alpha-chain or Stat6. While an expanded population of Th1 (IL-4-, IL-5-, IFN-gamma+, IL-2+) lymphocytes was observed in the same animals, surprisingly, cells with a mixed Th0 cytokine pattern were rare. The cytokine production phenotypes of the Th1 and Th2 subpopulations generated in infected Stat6-deficient mice were unaffected by in vitro neutralization of endogenous IL-4 or IFN-gamma. Nevertheless, while addition of exogenous rIL-12 resulted in transitory IFN-gamma production by Th2 lymphocytes from both wild-type and Stat6-deficient mice, IL-4 synthesis was preserved in the former, but temporarily ablated in the latter cells. Importantly, IL-4+ IFN-gamma- and IL-4- IFN-gamma+ populations similar to those arising in helminth-infected Stat6-deficient mice could also be generated in vitro by repetitive polyclonal stimulation of CD4+CD62Lhigh lymphocytes from uninfected mice of the same strain. Together, the results of these single cell analysis experiments demonstrate that IL-4R/Stat6 signaling, while influencing the final frequency of Th2 lymphocytes, is not essential for Th2 cell development, and suggest that this pathway has a previously unrecognized function in stabilizing Th2 populations once they have emerged.

Th1/Th2 balance in infection

Cytokines produced by T helper (Th) cells are of critical importance for the outcome of many infectious diseases. Producing the "right" set of cytokines in response to an infectious agent can be a matter of life or death. The Th1/Th2 dichotomy, although an oversimplification has proven useful in the analysis of immune responses to infections. In some infectious diseases, most notably leishmaniasis or infections with gastrointestinal helminths, one Th subset is indispensable for clearing the infection, whereas the opposite Th subset is detrimental. More frequently, both Th1 and Th2 responses are required at different time points to effectively eradicate an infectious agent. The granuloma responses to either Mycobacterium tuberculosis or Schistosoma mansoni provide illustrative examples and are discussed in this review. There is accumulating evidence for frequent coexpression of Th1 and Th2 cytokines during the in vivo immune response to infections. The mechanisms by which infectious agents modulate Th1/Th2 phenotype development are summarized here. Finally, we review here the current evidence for cytokine imbalances induced by infections as pathogenic or protective factors in autoimmunity and allergy.

Development of vaccines against human parasitic diseases: tools, current status and perspectives

Vaccines against malaria, leishmaniasis and schistosomiasis are in the most advanced stages of development of all vaccines for human parasitic diseases. Despite the remarkable progress made in identifying and producing protective antigens, at present there are no generally accepted vaccines against parasitic diseases. Vaccines for malaria and leishmaniasis have been taken to clinical trials while vaccines for schistosomiasis are in Phase I/II trials. This review will focus on the most promising antigenic preparations, emphasising the tools, present status and perspectives for development of vaccines against malaria, leishmaniasis and schistosomiasis.

IFN-gamma is necessary but not sufficient for anti-CD40 antibody-mediated inhibition of the Th2 response to Schistosoma mansoni eggs

The injection of Schistosoma mansoni eggs into the footpads of mice results in a localized Th2 cytokine response and tissue eosinophilia. We examined whether treatment with CD40-activating Abs would block the development of Th2 cytokine responses and eosinophilic tissue pathology in this model. Seven days after C57BL/6 mice were injected with eggs and the FGK45 anti-CD40 Ab, Ag-specific synthesis of IL-4, IL-5, and IL-13 in lymph node culture was reduced (>10-fold) relative to control mice treated with eggs and rat IgG. In contrast, IFN-gamma and IL-12 were increased in both culture supernatants and in the serum. Similar changes in lymph node cytokine mRNA were observed in vivo, and tissue eosinophilia was reduced nearly 20-fold. Th2 cytokine responses in anti-CD40-treated IFN-gamma-/- and IL-12 p40-/- C57BL/6 mice were unaffected, although anti-CD40 induced high levels of systemic and local IFN-gamma production in both wild-type and IL-12 p40-/- mice. We conclude that CD40-activating treatments strongly reverse the immune phenotype generated in response to a classic, Th2-biasing stimulus and stimulate IFN-gamma through a novel IL-12-independent pathway. This model for Th1-deviating immune therapy may have relevance to the treatment of Th2-dependent diseases in general.

CpG oligonucleotides can prophylactically immunize against Th2-mediated schistosome egg-induced pathology by an IL-12-independent mechanism

Using a Schistosoma mansoni egg-induced granuloma model, we examined the ability of CpG oligodeoxynucleotides (ODN) to suppress Th2-type cytokine expression and to prophylactically immunize against Th2-dependent pulmonary pathology. The mechanism was examined by studying Th2 response regulation in cytokine-deficient mice. Surprisingly, our findings revealed several functions of CpG DNA that were completely IL-12 independent. Most striking was the marked suppression in Th2 cytokine expression and granulomatous inflammation observed in egg/CpG-sensitized IL-12-deficient mice. Immune deviation was not dependent on NK or B cells. However, a role for IL-10, B7.1, and CD40 expression in Th2 response inhibition was suggested. Indeed, CpG ODN up-regulated all three elements in both wild-type and IL-12-deficient mice. The role of IL-10 was demonstrated in mice exhibiting combined deficiencies in IL-12 and IL-10. Here, a marked increase in egg-specific IL-4/IL-5-producing cells confirmed a role for both cytokines in Th2 response inhibition. Nevertheless, the frequency of Th2-producing cells was again reduced by CpG ODN. However, in marked contrast to IL-12-deficient animals, a significant increase in IFN-gamma-producing cells likely explains the reduced Th2 response in IL-10/IL-12-deficient mice. Thus, a novel IL-12-independent type 1-inducing pathway was revealed in the combined absence of IL-12 and IL-10. Together, these data demonstrate 1) that the Th1-promoting activity of CpG DNA is controlled by IL-12 and IL-10, and 2) that Th2 response inhibition by CpG ODN involves IL-12-independent changes in IL-10 and costimulatory molecule expression. These findings illustrate the utility of CpG DNA as adjuvants for vaccines designed to prevent Th2-dependent immunopathology.

Schistosomal egg antigen-responsive CD8 T-cell population in Schistosoma mansoni-infected BALB/c mice

We demonstrated here that schistosomal egg antigen (SEA) is able to stimulate an antigen-specific, cytotoxic CD8+ T-cell response in mice. Indeed, a single i.p. immunization with SEA resulted in the in vivo induction of significant cytotoxic T lymphocyte (CTL) activity in the spleen within 20 days. Effector cells were classic class I major histocompatibility complex (MHC)-restricted CD8+ lymphocytes producing interferon-gamma (IFN-gamma) and interleukin-2 (IL-2), suggesting a type 1 response to SEA. We therefore investigated the relevance of these observations in the context of the Schistosoma mansoni parasite infection. CTL activity against SEA-pulsed target cells was evidenced throughout the infection after in vitro stimulation of recovered splenic cells with SEA demonstrating that SEA-specific CD8+ T cells with cytotoxic potentialities are present during infection. This activity was strongly increased after immunization of mice with SEA like the production of IFN-gamma in the sera. A marked reduction in the number of granulomas and of fibrosis with the presence of cells producing IFN-gamma in the liver was also observed leading to the survival of SEA-immunized mice.

Coadministration of interleukin 12 expression vector with antigen 2 cDNA enhances induction of protective immunity against Coccidioides immitis

Interleukin 12 (IL-12) plays an important role in the induction of protective immunity against cancer and infectious diseases. In this study we asked whether IL-12 cDNA could increase the protective capacity of the antigen 2 (Ag2) gene vaccine in experimental coccidioidomycosis. Coimmunization of BALB/c mice with a single-chain IL-12 cDNA (p40-L-p35) and Ag2 cDNA, both subcloned into the pVR1012 plasmid, significantly enhanced protection against systemic challenge with 2,500 arthroconidia, as evidenced by a greater-than-1.3-log-unit reduction in the fungal load in the lungs and spleens compared to mice receiving the pVR1012 vector alone, Ag2 cDNA alone, or IL-12 cDNA alone. The enhanced protection was associated with increased gamma interferon secretion; production of immunoglobulin G2a (IgG2a), IgG2b, and IgG3 antibodies to Coccidioides immitis antigen; and the influx of CD4(+) and CD8(+) T cells in lungs and spleens. When challenged by the pulmonary route, mice covaccinated with Ag2 cDNA and IL-12 cDNA were not protected at the lung level but did show a significant reduction in the fungal load in their livers and spleens compared to mice vaccinated with Ag2 cDNA or IL-12 cDNA alone. These results suggest that IL-12 acts as a therapeutic adjuvant to enhance Ag2 cDNA-induced protective immunity against experimental coccidioidomycosis through the induction of Th1-associated immune responses.

The search for a vaccine against schistosomiasis--a difficult path but an achievable goal

The search for an effective vaccine against schistosomiasis, a parasitic disease currently affecting over 200 million people, remains a desirable but as yet challenging and elusive goal. Progress in the area has been relatively slow but research demonstrating the ability of humans to acquire natural immunity to schistosome infection, together with the successful use in animals of attenuated vaccines, supplemented with encouraging results obtained with defined antigens, suggests that development of a vaccine is achievable. Noteworthy also are recent immune correlate findings which shed light on the complex, putatively protective immune responses in humans, which have improved the prospects of success. With the first human clinical trial having been completed with a schistosome vaccine candidate, this review examines current progress aimed at achieving the objective of a safe and effective vaccine for widespread use against schistosomiasis. The review emphasises work undertaken in the author's laboratory and those of his chief collaborators in the search for a vaccine against schistosomiasis japonica, a disease of major public health significance in The People's Republic of China and The Philippines. Schistosomiasis vaccines should not be considered as the panacea for schistosomiasis control as, when available, it is generally envisaged that they would be used as one component of an integrated strategy complementing currently available and effective tools such as chemotherapy, improvements to sanitation, piped water supply, effective sewage draining and health education.

Vaccination against helminth parasites--the ultimate challenge for vaccinologists?

Helminths are multicellular pathogens which infect vast numbers of human and animal hosts, causing widespread chronic disease and morbidity. Vaccination against these parasites requires more than identification of effective target antigens, because without understanding the immunology of the host-parasite relationship, ineffective immune mechanisms may be invoked, and there is a danger of amplifying immunopathogenic responses. The fundamental features of the immune response to helminths are therefore summarised in the context of vaccines to helminth parasites. The contention between type-1 and type-2 responses is a central issue in helminth infections, which bias the immune system strongly to the type-2 pathway. Evidence from both human and experimental animal infections indicates that both lineages contribute to immunity in differing circumstances, and that a balanced response leads to the most favourable outcome. A diversity of immune mechanisms can be brought to bear on various helminth species, ranging from antibody-independent macrophages, antibody-dependent granulocyte killing, and nonlymphoid actions, particularly in the gut. This diversity is highlighted by analysis of rodent infections, particularly in comparisons of cytokine-depleted and gene-targeted animals. This knowledge of protective mechanisms needs to be combined with a careful choice of parasite antigens for vaccines. Many existing candidates have been selected with host antibodies, rather than T-cell responses, and include a preponderance of highly conserved proteins with similarities to mammalian or invertebrate antigens. Advantage has yet to be taken of parasite genome projects, or of directed searches for novel, parasite-specific antigens and targets expressed only by infective stages and not mature forms which may generate immunopathology. With advances under way in parasite genomics and new vaccine delivery systems offering more rapid assessment and development, there are now excellent opportunities for new antihelminth vaccines.

An IL-13 inhibitor blocks the development of hepatic fibrosis during a T-helper type 2-dominated inflammatory response

In schistosomiasis, chronic parasite egg-induced granuloma formation can lead to tissue destruction and fibrosis, which causes much of the morbidity and mortality associated with this disease. Here we show the importance of IL-13 in the pathogenesis of schistosomiasis, and demonstrate, perhaps for the first time, the therapeutic efficacy of an IL-13 inhibitor, sIL-13Ralpha2-Fc, in the control of hepatic fibrosis. T-helper type 2 (Th2) cytokines dominate the immune response in mice infected with Schistosoma mansoni, yet the specific contributions of IL-13 and IL-4 to the development of fibrosis were not previously investigated. Our studies demonstrate that both cytokines play redundant roles in granuloma formation, which explains the ability of IL-4-deficient mice to form granulomas around eggs. More importantly, however, these studies demonstrate that IL-13 is the dominant Th2-type cytokine regulating fibrosis. IL-13 stimulated collagen production in fibroblasts, and procollagen I and procollagen III mRNA expression was decreased in sIL-13Ralpha2-Fc-treated mice. Moreover, the reduction in fibrosis observed in IL-4-deficient mice was much less pronounced than that in sIL-13Ralpha2-Fc-treated animals. Fibrosis is a major pathological manifestation of a number of allergic, autoimmune, and infectious diseases. Thus, our findings provide evidence that IL-13 inhibitors may be of general therapeutic benefit in preventing damaging tissue fibrosis resulting from Th2-dominated inflammatory responses.

Increased levels of alternatively spliced interleukin 4 (IL-4delta2) transcripts in peripheral blood mononuclear cells from patients with systemic sclerosis

Recent in vitro studies have shown that interleukin 4 (IL-4) induces and gamma interferon (IFN-gamma) inhibits collagen production. To define the TH1(IFN-gamma) and TH2(IL-4) cytokine profiles in systemic sclerosis (Sscl), a disease characterized by widespread fibrosis, we investigated IL-4 and IFN-gamma transcripts in peripheral blood mononuclear cells and plasma protein levels in 13 patients with Sscl. Two previously identified IL-4 transcripts, a full-length transcript and an alternatively spliced (truncated) transcript (designated IL-4delta2), were identified in patients and normal controls. Significantly increased levels of total IL-4 transcripts (full-length plus IL-4delta2 transcripts) were found in patients with Sscl in comparison to those found in healthy controls (P = 0.003), and this increase was primarily due to an increase in the level of the alternatively spliced IL-4delta2 form. The IL-4delta2/full-length-IL-4 transcript ratio was significantly increased in Sscl patients (P < 0.0001, versus healthy controls). Sequencing analysis revealed that the frequency of IL-4 clones carrying the IL-4delta2 transcript was also substantially increased in patients with Sscl. Plasma IL-4 protein levels were increased in Sscl patients compared to those in healthy controls (P = 0.001) and correlated with total IL-4 transcript levels. The up-regulation of the fibrogenic IL-4 (a TH2 cytokine) in Sscl suggests a pathogenic role for IL-4 in this disease.

Interleukin-12 as an adjuvant for cancer immunotherapy

Interleukin-12 (IL-12) is a cytokine whose main effect is to drive Th-cell differentiation throughout a T helper type 1 cell type of response, thus inducing interferon gamma (IFNgamma) and favoring a switch from Ig to IgG2a. These properties make IL-12 a candidate adjuvant for vaccination against cancer and infection disease. Enthusiasm was generated in many animal studies where IL-12 was given either systemically or locally. The experience of some toxicity in humans has hampered its further development into clinical applications, which, however, are still possible if restricted to local administration. Gene transfer seems to be the preferred approach to obtain this local release of cytokine. Here we review the applications of IL-12 as adjuvant.

Severe hepatic fibrosis in Schistosoma mansoni infection is controlled by a major locus that is closely linked to the interferon-gamma receptor gene

Lethal disease due to hepatic periportal fibrosis occurs in 2%-10% of subjects infected by Schistosoma mansoni in endemic regions such as Sudan. It is unknown why few infected individuals present with severe disease, and inherited factors may play a role in fibrosis development. Schistosoma mansoni infection levels have been shown to be controlled by a locus that maps to chromosome 5q31-q33. To investigate the genetic control of severe hepatic fibrosis (assessed by ultrasound examination) causing portal hypertension, a segregation analysis was performed in 65 Sudanese pedigrees from the same village. Results provide evidence for a codominant major gene, with.16 as the estimated allele A frequency predisposing to advanced periportal fibrosis. For AA males, AA females, and Aa males a 50% penetrance is reached after, respectively, 9, 14, and 19 years of residency in the area, whereas for other subjects the penetrance remains <.02 after 20 years of exposure. Linkage analysis performed in four candidate regions shows that this major locus maps to chromosome 6q22-q23 and that it is closely linked (multipoint LOD score 3.12) to the IFN-gammaR1 gene encoding the receptor of the strongly antifibrogenic cytokine interferon-gamma. These results show that infection levels and advanced hepatic fibrosis in human schistosomiasis are controlled by distinct loci; they suggest that polymorphisms within the IFN-gammaR1 gene could determine severe hepatic disease due to S. mansoni infection and that the IFN-gammaR1 gene is a strong candidate for the control of abnormal fibrosis observed in other diseases.

Polarization of the immune response to the single immunodominant epitope of p38, a major Schistosoma mansoni egg antigen, generates Th1- or Th2-type cytokines and granulomas

In schistosomiasis mansoni, helminth eggs secrete soluble egg antigens (SEA) that induce T-cell-mediated granulomatous tissue responses. The cloned 38-kDa peptide (p38) of SEA was shown to induce and elicit Th1-type responsiveness in H-2(k) mice. Subsequently, the immunodominant T-cell epitope (P4) of p38 was shown to elicit pulmonary granuloma formation and Th1-type cytokine production in sensitized or infected mice. Here, we report that the immune response to p38 or P4 can be polarized to a Th1 or Th2 profile when the peptides are presented intraperitoneally in soluble recombinant interleukin-12 (IL-12) or alum adjuvant, respectively. The Th1 or Th2 profile was verified by cytokine secretion, enzyme-linked spot assay, and antibody isotype characterization. Importantly, the polarized immune response generated two types of pulmonary granulomas around injected P4-coated beads. The type 1 granulomas were smaller and contained mononuclear cells and occasional thin strands of deposited collagen. In contrast, the type 2 lesions were larger and contained mononuclear cells, large numbers of eosinophils, and several thick bands of deposited collagen. By reverse transcription-PCR cytokine, message in the type 1 granuloma-bearing lungs was found for gamma interferon, tumor necrosis factor alpha, and inducible nitric oxide synthase but not for IL-4 or IL-5. Conversely, lungs with type 2 granulomas had message only for IL-4 and IL-5. These results show that in the proper cytokine environment, the response to a strong Th1 inducer peptide can be deviated to a Th2 profile.

Intradermal Delivery of IL-12 Naked DNA Induces Systemic NK Cell Activation and Th1 Response In Vivo That Is Independent of Endogenous IL-12 Production

In this study four murine IL-12 naked DNA expression plasmids (pIL-12), containing both the p35 and p40 subunits, were shown to induce systemic biological effects in vivo after intradermal injection. Three of the four IL-12 expression vectors augmented NK activity and induced expression of the IFN-γ and IFN-γ-inducible Mig genes. Both IL-12 p70 heterodimer and IFN-γ proteins were documented in the serum within 24 h after intradermal injection of the pIL-12o− plasmid, which also induced the highest level of NK activity in the spleen and liver among the IL-12 constructs. Interestingly, both p40 mRNA expression at the injection site and serum protein levels followed a biphasic pattern of expression, with peaks on days 1 and 5. Subsequent studies revealed that the ability of intradermally injected pIL-12o− to augment NK lytic activity was prevented by administration of a neutralizing anti-IL-12 mAb. Finally, injection of the pIL-12o− into BALB/c IL-12 p40−/− mice also resulted in a biphasic pattern of IL-12 p70 appearance in the serum, and induced IFN-γ protein and activated NK lytic activity in liver and spleen. These results demonstrate that injection of delivered naked DNA encoding the IL-12 gene mediates the biphasic systemic production of IL-12-inducible genes and augments the cytotoxic function of NK cells in lymphoid and parenchymal organs as a direct result of transgene expression. The results also suggest that these naked DNA plasmids may be useful adjuvants for vaccines against infectious and neoplastic diseases.

Dose-dependent effects of IL-12 treatment to immune response induced after immunization with a recombinant respiratory syncytial virus (RSV) fusion protein fragment

The amino acid (aa) sequence 190-289 of the RSV fusion (F) glycoprotein expressed in insect cells (bF(190-289)) has been shown to partially protect BALB/c mice and to prime for a Th2 cell response. We evaluated the effects of IL-12 treatment during antigen priming of bF(190-289) on immune response and protective efficacy. Low doses of IL-12 (10 ng) reduced IL-4 and IL-5 secretion (but did not affect IL-10 production) and decreased inflammatory signs whereas high doses of IL-12 had no effects. In addition, IL-12 treatment did not improve resistance to RSV replication. These results suggest that IL-12 treatment attenuates Th2 response and Th2 associated pulmonary inflammatory response in a dose-dependent manner, without improving protective efficacy.

Intranasal Administration of a Schistosoma mansoni Glutathione S-Transferase-Cholera Toxoid Conjugate Vaccine Evokes Antiparasitic and Antipathological Immunity in Mice

Mucosal administration of Ags linked to cholera toxin B subunit (CTB) can induce both strong mucosal secretory IgA immune responses and peripheral T cell hyporeactivity. In this study, intranasal (i.n.) administration of CTB-conjugated Schistosoma mansoni 28-kDa GST (CTB-Sm28GST) was found to protect infected animals from schistosomiasis, especially from immunopathological complications associated with chronic inflammation. Worm burden and liver egg counts were reduced in infected animals treated with the CTB-Sm28GST conjugate as compared with mice infected only, or with mice treated with a control (CTB-OVA) conjugate. However, a more striking and consistent effect was that granuloma formations in liver and lungs of mice treated with CTB-Sm28GST were markedly suppressed. Such treatment was associated with reduced systemic delayed-type hypersensitivity and lymphocyte proliferative responses to Sm28GST. Production of IFN-γ, IL-3, and IL-5 by liver cells was also markedly reduced after i.n. treatment of CTB-Sm28GST, whereas IL-4 production was not impaired. Intranasal treatment of infected mice with CTB-Sm28GST increased IgG1-, IgG2a-, IgA-, and IgE-Ab-forming cell responses in liver in comparison with treatment with CTB-OVA, or free Sm28GST. Most importantly, mucosal treatment with CTB-Sm28GST significantly reduced animal mortality when administered to chronically infected mice. Our results suggest that it may be possible to design a therapeutic vaccine against schistosomiasis that both limits infection and suppresses parasite-induced pathology.

Studies with Double Cytokine-Deficient Mice Reveal That Highly Polarized Th1- and Th2-Type Cytokine and Antibody Responses Contribute Equally to Vaccine-Induced Immunity to Schistosoma mansoni

A fundamental obstacle to vaccine development in schistosomiasis mansoni is a lack of understanding of what type of an immune response should be invoked. We have addressed this central issue by using the radiation-attenuated cercariae vaccine in mice genetically engineered to exhibit highly polarized type 1 (IL-10/IL-4-deficient) or type 2 (IL-10/IL-12-deficient) cytokine and Ab phenotypes. Our data show that while significant differences in immunity exist after a single vaccination with irradiated cercariae in double cytokine-deficient vs wild-type mice, these differences disappear after two vaccinations. The most important finding of these studies, however, was revealed in vaccinated IL-10-deficient mice. These mice developed a mixed and elevated type 1- and type 2-associated immune response and developed anti-schistosome immunity at levels equal to or better than those in wild-type mice. This immunity in IL-10-deficient mice correlated with higher parasite-specific Ab titers, greater proliferative capacity of lymphocytes, increased frequency of IFN-γ- and IL-4-secreting cells, elevated perivascular/peribronchial inflammatory responses in the lung, and greater in vitro schistosomulacidal capacity of parasite Ag-elicited cells. These results suggest that optimal vaccine-induced immunity against schistosomes is linked not to the development of a highly polarized response, but, rather, to the induction of both type 1- and type 2-associated immune responses.

Liver fibrogenesis and the role of hepatic stellate cells: new insights and prospects for therapy

Hepatic fibrosis is a wound-healing response to chronic liver injury, which if persistent leads to cirrhosis and liver failure. Exciting progress has been made in understanding the mechanisms of hepatic fibrosis. Major advances include: (i) characterization of the components of extracellular matrix (ECM) in normal and fibrotic liver; (ii) identification of hepatic stellate cells as the primary source of ECM in liver fibrosis; (iii) elucidation of key cytokines, their cellular sources, modes of regulation, and signalling pathways involved in liver fibrogenesis; (iv) characterization of key matrix proteases and their inhibitors; (v) identification of apoptotic mediators in stellate cells and exploration of their roles during the resolution of liver injury. These advances have helped delineate a more comprehensive picture of liver fibrosis in which the central event is the activation of stellate cells, a transformation from quiescent vitamin A-rich cells to proliferative, fibrogenic and contractile myofibroblasts. The progress in understanding fibrogenic mechanisms brings the development of effective therapies closer to reality. In the future, targeting of stellate cells and fibrogenic mediators will be a mainstay of antifibrotic therapy. Points of therapeutic intervention may include: (i) removing the injurious stimuli; (ii) suppressing hepatic inflammation; (iii) down-regulating stellate cell activation; and (iv) promoting matrix degradation. The future prospects for effective antifibrotic treatment are more promising than ever for the millions of patients with chronic liver disease worldwide.

Schistosome-Infected IL-4 Receptor Knockout (KO) Mice, in Contrast to IL-4 KO Mice, Fail to Develop Granulomatous Pathology While Maintaining the Same Lymphokine Expression Profile

Th2 lymphocytes have been postulated to play a major role in the immunopathology induced by Schistosoma mansoni infection. Nevertheless, infected IL-4 knockout (KO) and wild-type (wt) mice develop egg granulomas comparable in size. To further investigate the function of the Th2 response in egg pathology we studied IL-4Rα-deficient mice, which are nonresponsive to both IL-4 and IL-13. In striking contrast to IL-4 KO animals, infected IL-4Rα KO mice developed only minimal hepatic granulomas and fibrosis despite the presence of CD3+ T cells in the residual egg lesions. Moreover, liver lymphokine mRNA levels in these animals and IL-4 KO mice were equivalent. In addition, infected IL-4Rα-deficient, IL-4-deficient, and wt animals developed similar egg Ag-specific IgG Ab titers, arguing that CD4-dependent Th activity is intact in KO mice. As expected, IFN-γ secretion was strongly up-regulated in mesenteric lymph node cultures from both groups of deficient animals, a change reflected in increased serum IgG2a and IgG2b Ab levels. Surprisingly, Th2 cytokine production in infected IL-4Rα KO mice was not abolished but was only reduced and resembled that previously documented in IL-4 KO animals. This residual Th2 response is likely to explain the ability of IL-4 KO mice to generate egg granulomas, which cannot be formed in IL-4Rα-deficient animals because of their lack of responsiveness to the same cytokine ligands. Taken together, these findings argue that tissue pathology in schistosomiasis requires, in addition to egg-specific CD4+ lymphocytes, a previously unrecognized IL-4Rα+ non-T cell effector population.

A fatty acid binding protein from Fasciola hepatica induced protection in C57/BL mice from challenge infection with Schistosoma bovis

Three strains of mice (NMRI, C57/BL, BALB/c) were each immunized with a 12 kDa purified, native Fasciola hepatica fatty acid binding protein (Fh12) and challenged percutaneously with Schistosoma bovis cercariae. C57/BL mice immunized with Fh12 had significant reductions in S. bovis worm burden recoveries (96 and 87% reductions over controls in two separate experiments). When using NMRI or BALB/c mice, Fh12 alone or in Freund's adjuvant failed to induce significant protection against S. bovis. In C57/BL mice vaccinated against Fh 12, antibodies to the IgG2a isotype, but not to the IgG1 isotype, increased by 2 weeks after the second immunization and remained high through 8 weeks of S. bovis infection. Antibodies to S. bovis increased after 4 weeks of infection. Regarding cytokine production by spleen mononuclear cells, C57/BL mice vaccinated with Fh12 in adjuvant, and having the highest protective response against challenge infection with S. bovis, had an increase of IFN-gamma production with Concanavalin A but no increase of IL-4 in similarly stimulated cells. These results suggest that the protection obtained in this group of mice is mediated by a Th1 immune response.

Long Term Prevention of Allergic Lung Inflammation in a Mouse Model of Asthma by CpG Oligodeoxynucleotides

Asthma is an inflammatory disease of the airways that is induced by Th2 cytokines and inhibited by Th1 cytokines. Despite a steady increase in the incidence, morbidity, and mortality from asthma, no current treatment can reduce or prevent asthma for a prolonged period. We examined the ability of unmethylated CpG oligodeoxynucleotides (ODN), which are potent inducers of Th1 cytokines, to prevent the inflammatory and physiological manifestations of asthma in mice sensitized to ragweed allergen. Administration of CpG ODN 48 h before allergen challenge increased the ratio of IFN-γ to IL-4 secreting cells, diminished allergen-induced eosinophil recruitment, and decreased the number of ragweed allergen-specific IgE-producing cells. These effects of CpG ODN were sustained for at least 6 wk after its administration. Furthermore, there was a vigorous Th1 memory response to the recall Ag, inhibition of peribronchial and perivascular lung inflammation, and inhibition of bronchial hyperresponsiveness 6 wk after administration of CpG ODN. Administration of CpG ODN in IFN-γ −/− mice failed to inhibit eosinophil recruitment, indicating a critical role of IFN-γ in mediating these effects. This is the first report of a treatment that inhibits allergic lung inflammation in presensitized animals for a prolonged period and thus has relevance to the development of an effective long term treatment for asthma.

Induction of resistance against Schistosoma mansoni infection by passive transfer of an IgG2a monoclonal antibody

Monoclonal antibodies can confer resistance to schistosome infections. This has led to identification of several protective antigens. An IgG2a monoclonal antibody designated BRL4 mAb identified a 74-kDa antigen in antigenic extract of Schistosoma mansoni adult worms. The target antigen was localized in gut and tegument. In 3 passive transfer experiments, the BRL4 mAb conferred 51.6, 41.9 and 53.8% protection levels into female Swiss mice. Histopathological examination revealed a marked decrease in number, size, collagen and reticular fibers of the liver granulomas. Further experiments using purified 74-kDa-target antigen as a candidate vaccine will be performed.

Interleukin-12 as an adjuvant for an antischistosome vaccine consisting of adult worm antigens: protection of rats from cercarial challenge

Our group previously demonstrated that a detergent extract (fraction S3) prepared from immature (4-week) Schistosoma mansoni parasites can induce partial, serum-transferable immunity to challenge infection in rats when administered as an alum precipitate. In the present study, we examined whether S3 prepared from adult (7-week) worms could similarly induce protection and whether immunity could be positively influenced by treatment with interleukin-12 (IL-12). IL-12 coadministered to Fischer rats and C57BL/6 mice at the time of S3 vaccination altered the prechallenge kinetics of S3-specific antibody titers in both species, ultimately leading to a stable enhancement of titers (relative to those in animals vaccinated without IL-12) in mice but not rats. Immunoblot analysis of prechallenge immune sera demonstrated that IL-12 treatment was associated with changes in the S3 antigen recognition profile in each species. Isotyping of specific antibodies in S3- plus IL-12-vaccinated mice prior to challenge infection revealed a moderate elevation in immunoglobulin G1 (IgG1) responses, strongly enhanced IgG2a and IgG2b responses, as well as diminished total serum IgE responses compared to those in mice given S3 only. In vaccinated rats, IL-12 profoundly suppressed specific IgG1 and enhanced IgG2b responses but did not affect IgG2a responses. S3- plus IL-12-vaccinated rats also produced less total IgE upon challenge infection. Enumeration of worm burdens revealed that vaccination with S3 plus IL-12 conferred 50% protection from cercarial challenge to rats, whereas rats given S3 only were not protected; mice were not protected by S3 vaccination regardless of IL-12 coadministration. The protection observed in S3- plus IL-12-vaccinated rats could not be transferred with serum, suggesting participation of an activated cellular component in the expression of immunity.

Interleukin-12 is capable of generating an antigen-specific Th1-type response in the presence of an ongoing infection-driven Th2-type response

Previously we demonstrated that recombinant murine interleukin-12 (rmIL-12) administration can promote a primary Th1 response while suppressing the Th2 response in mice primed with 2,4, 6-trinitrophenyl-keyhole limpet hemocyanin (TNP-KLH). The present studies examined the capacity of rmIL-12 to drive a Th1 response to TNP-KLH in the presence of an ongoing Th2-mediated disease. To establish a distinct Th2 response, we used a murine model of leishmaniasis. Susceptible BALB/c mice produce a strong Th2 response when infected with Leishmania major and develop progressive visceral disease. On day 26 postinfection, when leishmaniasis was well established, groups of mice were immunized with TNP-KLH in the presence or absence of exogenous rmIL-12. Even in the presence of overt infection, TNP-KLH-plus-rmIL-12-immunized mice were still capable of generating KLH-specific gamma interferon (IFN-gamma) as well as corresponding TNP-specific immunoglobulin G2a (IgG2a) titers. In addition, the KLH-specific IL-4 was suppressed in infected mice immunized with rmIL-12. However, parasite-specific IL-4 and IgG1 production with a lack of parasite-specific IFN-gamma secretion were maintained in all infected groups of mice including those immunized with rmIL-12. These data show that despite the ongoing infection-driven Th2 response, rmIL-12 was capable of generating an antigen-specific Th1 response to an independent immunogen. Moreover, rmIL-12 administered with TNP-KLH late in infection did not alter the parasite-specific cytokine or antibody responses.

The p47(phox-/-) mouse model of chronic granulomatous disease has normal granuloma formation and cytokine responses to Mycobacterium avium and Schistosoma mansoni eggs

Chronic granulomatous disease (CGD) is a genetic disorder of NADPH oxidase in which phagocytes are defective in generating reactive oxidants. CGD patients suffer from recurrent infections and exuberant and persistent tissue granuloma formation. We hypothesized that abnormal granulomata in CGD may result from aberrant T-cell-mediated cytokine responses. To assess Th-1-type cytokine responses and granulomata, we challenged p47(phox-/-) and wild-type mice with avirulent (SmD) or virulent (SmT) variants of Mycobacterium avium 2-151. To assess Th-2-type cytokine responses and granulomata, we used Schistosoma mansoni eggs (SME). Mononuclear cells were harvested, and cytokine responses were determined by enzyme-linked immunosorbent assay or reverse transcriptase PCR. Following SmD or SmT challenge, splenocytes from p47(phox-/-) and wild-type mice generated similar polar Th-1 responses (increased levels of gamma interferon and basal levels of interleukin 4 [IL-4] and IL-5). By 8 weeks after SmT challenge, exuberant splenic granulomata developed in p47(phox-/-) and wild-type mice. After SME challenge, thoracic lymph node mononuclear cells from p47(phox-/-) and wild-type mice generated similar mixed Th-1 and Th-2 cytokine responses to SME antigen and concanavalin A. Peak lung granuloma sizes and rates of regression were similar in p47(phox-/-) and wild-type mice. These results suggest that exuberant granulomatous inflammation in CGD is probably not the result of skewing of T-cell responses toward the Th-1 or Th-2 pole. Appropriate regression of established tissue granulomata in p47(phox-/-) mice challenged with SME suggests that abnormal granuloma formation in CGD is stimulus dependent and is not an invariant feature of the disease.

HLA-DR-DQ alleles and HLA-DP alleles are independently associated with susceptibility to different stages of post-schistosomal hepatic fibrosis in the Chinese population

Abstract: Evaluation of human leukocyte antigen (HLA) class I and class II genes was performed on patients from China with Schistosomiasis japonica. Patients were categorized as grade 0 (n=44), grade I (n=81), grade II (n=99), or grade III (n=6) based on increasing severity of hepatic fibrosis due to repeated Schistosoma japonicum infections. These results show that the HLA-DRB1*1101-DQA1*0501-DQB1*0301 (Pc<0.02) and HLA-DRB1*1501-DRB5*0101 (Pc<0.02) haplotypes are associated with protection and susceptibility to grade I fibrosis, respectively, and that the HLA-DPA1*0103 -DPB1*0201 haplotype (Pc<0.02) is associated with protection from both grade II and III severe fibrosis. There was no association between HLA-B DNA haplotypes and the disease. These findings indicate that the HLA-class II molecules play a role in preventing or promoting fibrotic liver change after deposition with Schistosome eggs. Moreover, a tendency was observed within the HLA class II genes for the HLA-DR-DQ alleles to be associated with protection against early changes in liver fibrosis, whereas HLA-DP alleles were associated with protection from the late phase of fibrosis or severe hepatosplenic schistosomiasis.

Evolution of the type-1 (Th1)-type-2 (Th2) cytokine paradigm

During the past 12 years, since the discovery of murine Th1 and Th2 clones, increasing numbers of cells that make type-1 and type-2 cytokines have been recognized, and a growing number of these cytokines have been described. Emphasis has shifted from the CD4+ T cell, as the source of Th1-Th2 cytokines, to the functional effect of the type-1 and type-2 cytokines, independent of their cell of origin. Appreciation of the complex interactions of CMI and humoral immune responses continues to evolve. If this new paradigm provides insight into infectious disease pathogenesis and prevention, then it should allow development of new vaccines and vaccine adjuvants against these diseases.

Enhanced Th1 and dampened Th2 responses synergize to inhibit acute granulomatous and fibrotic responses in murine schistosomiasis mansoni

In murine schistosomiasis mansoni, CD4(+) Th1 and Th2 cells participate in the ovum-induced granulomatous inflammation. Previous studies showed that the interleukin-12 (IL-12)-induced Th1 response strongly suppressed the Th2-cell-mediated pulmonary granuloma development in naive or primed mice. However, liver granulomas were only moderately suppressed in egg-vaccinated, recombinant IL-12 (rIL-12)-treated infected mice. The present study shows that repeated rIL-12 injections given during early granuloma development at 5 to 7 weeks after infection prolonged the Th1 phase and resulted in gamma interferon-mediated suppression of liver granulomas. The timing is crucial: if given at 6 to 8 weeks, during the Th2-dominated phase of florid granuloma growth, the treatment is ineffective. Daily injections of rIL-12 given between 5 and 7.5 weeks during the period of granuloma growth achieved a somewhat-stronger diminution in granuloma growth with less deposition of collagen but caused 60% mortality and liver pathology. In contrast, combined treatment with rIL-12 and anti-IL-4-anti-IL-10 monoclonal antibody (MAb) injections given during the Th2 phase strongly inhibited liver granuloma growth without mortality. The diminished inflammatory response was accompanied by less deposition of collagen in the liver. Moreover, neutralization of endogenous IL-12 by anti-IL-12 MAbs effectively decreased the early Th1 phase (between 5 and 6 weeks after infection) but not the developing Th2 phase (5 to 7 weeks) of granuloma development. These studies indicate that the granulomatous response in infected mice can be manipulated by utilizing the Th1-Th2-subset antagonism with potential salutary results in the amelioration of fibrous pathology.

Role of cytokines in the formation and downregulation of hepatic circumoval granulomas and hepatic fibrosis in Schistosoma mansoni-infected mice

Schistosoma mansoni infections are associated with a strong Th2 cytokine response. Treatment of mice with IL-12 or anti-IL-2 or anti-IL-4 before i.v. injection of eggs increased IFN-gamma production and downregulated Th2 responses and pulmonary granuloma size. Conversely, anti-IFN-gamma antibody treatment increased Th2 responses and granuloma size. Similar manipulation produced less dramatic results in infected mice. However, sensitization of mice with eggs + IL-12 before infection augmented the Th1 response and decreased Th2 cytokines, granuloma size and fibrosis. Antisera to IFN-gamma, TNF-alpha or IL-12 during IL-12-egg immunization partly restored granuloma size and fibrosis following infection. Variations in the size of granulomas in acute (8 week) infections may be influenced primarily by the number and state of activation of T cells. In chronic (12-16 week) infections immunologic downmodulation proceeded normally in mice without functional CD8+ cells and in IFN-gamma KO mice but not in B cell KO (microMT) mice or in mice deficient in FcR expression in spite of the fact that these mice downregulated their T cell and cytokine responses. It is evident that the participation of cytokines in granuloma formation and regulation is complicated and that the mechanisms controlling both these phenomena are likely to involve both T cells and antibody/FcR interactions.

The initiation and function of Th2 responses during infection with Schistosoma mansoni

Through experiments in which pro-inflammatory mediators have been neutralized in schistosomeinfected WT and IL-4 -/- mice we have been investigating the nature of the immune response that is required to allow survival during the period of acute disease that accompanies the onset of egg production by the parasitic worms. The developing picture is that of an early pro-inflammatory type-1 like response (characterized by the production of IFN-gamma and TNF-alpha and NO) which in the short term is able to control the deleterious effects on the liver associated with the arrival of the eggs, followed rapidly by a potent egg-induced Th2 response which simultaneously subsumes the role of protecting the liver and downregulates the production of the inflammatory mediators, thereby averting the serious consequence associated with the continued high level production of NO. Current research is directed towards: 1) understanding how pro-inflammatory mediators are protective during schistosomiasis, and 2) elucidating the underlying mechanisms through which the Th response is biased in a Th2 direction following exposure to schistosome eggs.

IL-10 Gene Knockout Mice Show Enhanced Th1-Like Protective Immunity and Absent Granuloma Formation Following Chlamydia trachomatis Lung Infection

We previously reported that higher IL-10 production is correlated with lower IFN-γ production, weaker delayed hypersensitivity (DTH), and slower organism clearance following chlamydial infection in mice. To assess more directly the role of IL-10, we examined protective immunity and pathological reaction in C57BL/6 IL-10 gene knockout (KO) and wild-type mice. The results showed that in the absence of endogenous IL-10, mice had significantly accelerated chlamydial clearance and developed significantly stronger DTH responses, which could be inhibited by local delivery of rIL-10. Consistent with the enhancement of DTH responses, IL-10 KO mice showed stronger and more persistent CD4 T cell-dependent IFN-γ production and significant elevation of IL-12 and TNF-α production. Additionally, wild-type, but not IL-10 KO, mice showed granuloma formation that was correlated with higher levels of Th2 cytokine (IL-5) production at the later stages of infection. Moreover, chlamydial infection, unlike parasitic protozoan infection, did not induce significant acute toxicity in IL-10 KO mice, which may be due to the low (undetectable) levels of systemic release of proinflammatory cytokines. These results suggest that IL-10 inhibits the priming and expansion of Th1-like T cell responses and that IL-10 plays a role in the fibrotic reaction seen with chlamydial infection.

IL-13 Is a Key Regulatory Cytokine for Th2 Cell-Mediated Pulmonary Granuloma Formation and IgE Responses Induced by Schistosoma mansoni Eggs

Schistosoma mansoni egg-induced pulmonary granuloma formation is a cell-mediated inflammatory response associated with dominant Th2-type cytokine expression, tissue eosinophilia, and high levels of serum IgE. In the present study, we show that in vivo blockade of the Th2 cytokine IL-13, using soluble IL-13R α2-Fc fusion protein, significantly reduced the size of pulmonary granulomas in unsensitized as well as egg-sensitized mice. Blocking IL-13 also significantly reduced total serum IgE levels. Interestingly, however, IL-13 blockade did not affect the evolving egg-induced Th2-type cytokine response. IL-4, IL-5, as well as IL-13 responses were indistinguishable in control-Fc- and soluble IL-13R α2-Fc fusion protein-treated animals. The smaller granulomas were also phenotypically like the control Fc-treated mice, displaying a similar eosinophil content. Additional studies in IL-4-deficient mice demonstrated that IL-13 was produced, but at much lower levels than in wild-type mice, while IL-4 expression was completely independent of IL-13. Moreover, while granuloma formation was partially reduced in IL-4-deficient mice, blocking IL-13 in these animals almost completely abrogated granuloma development and the pulmonary eosinophilia, while it simultaneously increased IFN-γ production. Together, these data demonstrate that IL-13 serves as an important mediator of Th2-mediated inflammation and plays a role in eliciting IgE responses triggered by schistosome eggs.

Induction of a protective immunity against Schistosoma mansoni with ovalbumin-coupled Sm37-5 coadsorbed with granulocyte-macrophage colony stimulating factor (GM-CSF) or IL-12 on alum

A previous study has shown that Sm37-5 is a major B cell epitope of Sm37-GAPDH. This epitope is highly antigenic in human infections and IgG antibody reactivity toward this determinant is associated with adolescent resistance to reinfection. This led us to test a synthetic peptide corresponding to Sm37-5, coupled to ovalbumin, as an anti-schistosome vaccine. Although mice injected with Sm37-5-OVA in Freund's adjuvant showed significant protection, immunization in aluminium hydroxide failed to induce protection. The adjuvant effect of cytokines (GM-CSF or IL-12) associated with the antigen on alum was investigated. With each of these two cytokines, significant reductions in the worm burden were obtained (32-38% with GM-CSF and 27% with IL-12, respectively). In addition, a reduction of the egg number trapped in the liver of immunized mice was also observed. Thus, protections were obtained with formulations that could potentially be used in humans.

Use of Intranasal IL-12 to Target Predominantly Th1 Responses to Nasal and Th2 Responses to Oral Vaccines Given with Cholera Toxin

We have investigated the effects of IL-12 and cholera toxin (CT) on the immune response to tetanus toxoid (TT) given by intranasal or oral routes. CT inhibited IL-12-induced IFN-γ secretion both in vivo and in vitro. Intranasal administration of IL-12 to mice nasally immunized with the combined vaccine of TT and CT resulted in increased TT-specific IgG2a and IgG3 Abs, while IgG1 and IgE Ab responses were markedly reduced. This shift of the CT-induced immune response toward Th1 type was associated with TT-specific CD4+ T cells secreting IFN-γ and reduced levels of Th2-type cytokines (i.e., IL-4, IL-5, IL-6, and IL-10). In contrast, intranasal IL-12 enhanced the CT-induced serum IgG1 and IgE Ab responses in mice given the combined vaccine orally. IFN-γ secretion by TT-specific CD4+ T cells was also enhanced; however, Th2-type cytokine responses were predominant. Mucosal secretory IgA responses to oral or nasal vaccines were not affected by intranasal IL-12. Thus, intranasal IL-12 delivery influences Th cell subset development in mucosal inductive sites that are dependent on the route of vaccine delivery.

Vaccines against human parasitic diseases: an overview

There are no vaccines currently available to control the major human parasitic diseases, although there is evidence of acquired immunity and resistance to reinfection in most of the parasitic infections. The present manuscript concentrates on the vaccines for parasitic diseases that are in the most advanced stages of development: malaria, leishmaniasis and schistosomiasis. Vaccines for malaria and leishmaniasis have been taken to clinical trials while vaccines for schistosomiasis are being considered for Phase I (assessment of safety and immune responsiveness in volunteers). We have attempted to give a factual account of the present status of knowledge of vaccines against human parasitic diseases, emphasizing both the successes and setbacks. We do not intend to cover the enormous literature in the field but have concentrated on the most promising antigenic preparations. Finally, some new approaches for the development of vaccines are discussed including nucleic acid vaccines and the use of cytokines as adjuvants.

Evaluation of IL-12 in Immunotherapy and Vaccine Design in Experimental Mycobacterium avium Infections

IL-12 is a pivotal cytokine in the induction of IFN-γ-mediated protective immune responses. We tested the effects of rIL-12 administration to Mycobacterium avium-infected mice and found a limited ability to induce protection against the infection; this ability varied according to the mycobacterial strain studied. IL-12 accelerated the expression and production of IFN-γ in both immunocompetent and immunodeficient SCID or CD4-depleted mice. Evidence of NK cell activation was found as well as an enhancement of the ability to adoptively transfer resistance with T cell-enriched spleen cell populations and an increase in inflammatory cell recruitment in the liver. The protective ability of IL-12 was dependent upon the endogenous production of IFN-γ as evaluated by the use of specific neutralizing Abs or IFN-γ gene-disrupted mice. IL-12 potentiated the protective immunity conferred by a subunit vaccine containing M. avium culture filtrate proteins and dimethyl dioctadecyl ammonium chloride as an adjuvant. Thus, we show limited immunotherapeutic benefits from IL-12 administration in M. avium infections and promising results in its use as a coadjuvant in vaccine design.

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.

IFN-γ, IL-12, and TNF-α Are Required to Maintain Reduced Liver Pathology in Mice Vaccinated with Schistosoma mansoni Eggs and IL-12

The development of hepatic fibrosis and portal hypertension is the principal cause of morbidity and mortality in schistosomiasis mansoni. Nevertheless, relatively little is known about the mechanisms that lead to excessive collagen deposition during infection with Schistosoma mansoni. In the murine model, infection leads to significant egg-induced granuloma formation, tissue eosinophilia, and hepatic fibrosis. The pathology has been linked to dominant type 2 cytokine expression, and our recent studies showed that sensitizing animals to egg Ags in combination with IL-12, before infection, led to a highly significant reduction in egg-induced immunopathology. In this study, we demonstrate that in contrast with egg/IL-12-sensitized animals that showed marked decreases in pathology, mice similarly sensitized but depleted of IFN-γ, IL-12, or TNF-α at the time of egg laying developed granulomas that were similar to the non-IL-12-treated control group. Although all three anti-cytokine-treated groups exhibited a dominant type 1 response in lymph node cells restimulated ex vivo, the expression of type 2 cytokine mRNA was markedly restored at the site of granuloma formation, which suggests that all three cytokines are required to maintain the suppressed type 2 pattern. Moreover, egg/IL-12-sensitized mice depleted of IFN-γ or IL-12 displayed a partial reduction in IFN-γ production, suggesting that multiple type 1 cytokines were required to maintain polarized type 1 responses to chronic type 2-inducing stimuli. Together, these data reveal key roles for IFN-γ, IL-12, and TNF-α in the protective effects mediated by this IL-12-based vaccine to prevent pathology.