Failure of P strain mice to respond to vaccination against schistosomiasis correlates with impaired production of IL-12 and up-regulation of Th2 cytokines that inhibit macrophage activation

In contrast to most inbred strains, P mice fail to develop significant resistance to Schistosoma mansoni infection as a result of vaccination with either radiation-attenuated cercariae or schistosome antigens plus Bacillus Calmette Guérin, and this failure correlates with defects in macrophage larvicidal activity. Supernatant fluids from antigen-treated in vitro cultures of splenocytes from vaccinated P mice demonstrate less macrophage stimulatory activity than do supernatants from cells of vaccine-responsive strains such as C57BL/6. This is not due either to diminished production of the macrophage-activating cytokine IFN-gamma by P mice, or to a lesser responsiveness of macrophages from P mice to activation by IFN-gamma. Rather, P splenocytes produce two-to threefold higher amounts of IL-4 and IL-10, cytokines which down-regulate the cytotoxic potential of IFN-gamma-treated macrophages. Thus, the macrophage-activating potential of cytokine preparations from vaccinated P mice can be completely recovered by in vitro treatment with antibodies to IL-4 or IL-10. Moreover, lower levels of IL-12, a cytokine involved in promoting development of Th1 responses, are produced by splenocytes from P mice as compared to C57BL/6 counterparts. These studies indicate that a genetic predisposition toward an impaired production of IL-12 and an increased production of down-regulatory Th2 cytokines correlate with low response to vaccination against S. mansoni.

IL-10 regulates liver pathology in acute murine Schistosomiasis mansoni but is not required for immune down-modulation of chronic disease

We have used IL-10 gene knockout mice (IL-10T) to examine the role of endogenous IL-10 in the down-modulation of hepatic granuloma formation and lymphocyte responses that occurs in chronic infection with the helminth parasite Schistosoma mansoni. Although IL-10-deficient animals showed 20 to 30% mortality between 8 and 14 wk postinfection, they displayed no alterations in their susceptibility to infection and produced similar numbers of eggs as their wild-type littermates. The IL-10T mice displayed a significant increase in hepatic granuloma size at the acute stage of infection, which was associated with increased IFN-gamma, IL-2, IL-1beta, and TNF-alpha mRNA expression in liver and elevated Th1-type cytokine production by lymphoid cells. Despite developing an enhanced Th1-type cytokine response, the IL-10T mice showed no consistent decrease in their Th2-type cytokine profile. Surprisingly, although granulomatous inflammation was enhanced at the acute stage of infection, the livers of IL-10T mice displayed no significant increase in fibrosis and underwent normal immune down-modulation at the chronic stage of infection. Moreover, the down-modulated state could be induced in IL-10T mice by sensitizing the animals to schistosome eggs before infection, further demonstrating that the major down-regulatory mechanism is not dependent upon IL-10. We conclude that while IL-10 plays an important role in controlling acute granulomatous inflammation, it plays no essential role in the process of immune down-modulation in chronic schistosome infection.

CD4+ T cell-mediated granulomatous pathology in schistosomiasis is downregulated by a B cell-dependent mechanism requiring Fc receptor signaling

The effector functions of CD4+ T lymphocytes are generally thought to be controlled by distinct populations of regulatory T cells and their soluble products. The role of B cells in the regulation of CD4-dependent host responses is less well understood. Hepatic egg granuloma formation and fibrosis in murine schistosomiasis are dependent on CD4+ lymphocytes, and previous studies have implicated CD8+ T cells or cross-regulatory cytokines produced by T helper (Th) lymphocytes as controlling elements of this pathologic process. In this report, we demonstrate that B cell-deficient (muMT) mice exposed to Schistosoma mansoni develop augmented tissue pathology and, more importantly, fail to undergo the spontaneous downmodulation in disease normally observed during late stages of infection. Unexpectedly, B cell deficiency did not significantly alter T cell proliferative response or cause a shift in the Th1/Th2 balance. Since schistosome-infected Fc receptor-deficient (FcR gamma chain knockout) mice display the same exacerbated egg pathology as that observed in infected muMT mice, the B cell- dependent regulatory mechanism revealed by these experiments appears to require receptor-mediated cell triggering. Together, the data demonstrate that humoral immune response/FcR interactions can play a major role in negatively controlling inflammatory disease induced by CD4+ T cells.

Analysis of granuloma formation in double cytokine-deficient mice reveals a central role for IL-10 in polarizing both T helper cell 1- and T helper cell 2-type cytokine responses in vivo

In response to i.v.-injected eggs of Schistosoma mansoni, normal mice develop a dominant type 2 response, whereas IL-10-deficient animals generate a mixed type 1/type 2 cytokine profile and show reduced pulmonary granuloma formation. IL-4-deficient mice, while displaying diminished type 2 responses and granulomatous inflammation, also do not fully default to a type 1 cytokine profile. Strikingly, mice doubly deficient in IL-4 and IL-10 are completely defective in pulmonary granuloma formation and develop a highly polarized type 1 cytokine pattern. In analogous fashion, mice deficient in both IL-12 and IL-10 generate highly exacerbated type 2 cytokine responses, whereas in wild-type animals, IL-12 depletion minimally effects egg-induced cytokine production. Together, these results argue first that IL-10 is an important endogenous down-regulator of type 2 as well as type 1 cytokine synthesis, and second, that its induction is critical for type 2 response polarization in vivo.

Analysis of granuloma formation in double cytokine-deficient mice reveals a central role for IL-10 in polarizing both T helper cell 1- and T helper cell 2-type cytokine responses in vivo

In response to i.v.-injected eggs of Schistosoma mansoni, normal mice develop a dominant type 2 response, whereas IL-10-deficient animals generate a mixed type 1/type 2 cytokine profile and show reduced pulmonary granuloma formation. IL-4-deficient mice, while displaying diminished type 2 responses and granulomatous inflammation, also do not fully default to a type 1 cytokine profile. Strikingly, mice doubly deficient in IL-4 and IL-10 are completely defective in pulmonary granuloma formation and develop a highly polarized type 1 cytokine pattern. In analogous fashion, mice deficient in both IL-12 and IL-10 generate highly exacerbated type 2 cytokine responses, whereas in wild-type animals, IL-12 depletion minimally effects egg-induced cytokine production. Together, these results argue first that IL-10 is an important endogenous down-regulator of type 2 as well as type 1 cytokine synthesis, and second, that its induction is critical for type 2 response polarization in vivo.

Fc epsilonRI-deficient mice infected with Schistosoma mansoni mount normal Th2-type responses while displaying enhanced liver pathology

The IgE/Fc epsilonRI interaction is postulated to play an important role in resistance to helminths both at the level of anti-parasitic effector cell function and in the initiation of Th2 responses through IL-4 produced by Fc epsilonRI+ non-B, non-T (NBNT) cells. To formally evaluate the role of IgE/Fc epsilonRI signaling in the host response to helminths we studied Schistosoma mansoni infection in Fc epsilonRI knockout (KO) mice. Infected wild-type (wt) and KO animals showed comparable adult worm and tissue egg burdens, arguing against a role for Fc epsilonRI interactions in host resistance. Significantly, NBNT cells from infected KO, in contrast to wt animals, did not secrete IL-4 when stimulated with anti-IgE Ab or soluble parasite Ag. Nevertheless, serum IgE levels and Th2 cytokine production profiles were comparable in both strains of mice, demonstrating that the Ag-dependent stimulation of IL-4 secretion by NBNT cells is not essential for helminth-induced Th2 differentiation. However, when stimulated with low Ag doses, splenocytes from infected Fc epsilonRI-deficient mice produced less IL-4 in vitro than similar cultures from infected wt animals, an effect attributable to their defective NBNT cell function. Moreover, infected KO mice showed enhanced egg granuloma formation and hepatic fibrosis, revealing that the IgE/Fc epsilonRI interaction, while not essential for Th2 response development or resistance to primary infection, plays a significant role in down-regulating host pathology.

Fc epsilonRI-deficient mice infected with Schistosoma mansoni mount normal Th2-type responses while displaying enhanced liver pathology

The IgE/Fc epsilonRI interaction is postulated to play an important role in resistance to helminths both at the level of anti-parasitic effector cell function and in the initiation of Th2 responses through IL-4 produced by Fc epsilonRI+ non-B, non-T (NBNT) cells. To formally evaluate the role of IgE/Fc epsilonRI signaling in the host response to helminths we studied Schistosoma mansoni infection in Fc epsilonRI knockout (KO) mice. Infected wild-type (wt) and KO animals showed comparable adult worm and tissue egg burdens, arguing against a role for Fc epsilonRI interactions in host resistance. Significantly, NBNT cells from infected KO, in contrast to wt animals, did not secrete IL-4 when stimulated with anti-IgE Ab or soluble parasite Ag. Nevertheless, serum IgE levels and Th2 cytokine production profiles were comparable in both strains of mice, demonstrating that the Ag-dependent stimulation of IL-4 secretion by NBNT cells is not essential for helminth-induced Th2 differentiation. However, when stimulated with low Ag doses, splenocytes from infected Fc epsilonRI-deficient mice produced less IL-4 in vitro than similar cultures from infected wt animals, an effect attributable to their defective NBNT cell function. Moreover, infected KO mice showed enhanced egg granuloma formation and hepatic fibrosis, revealing that the IgE/Fc epsilonRI interaction, while not essential for Th2 response development or resistance to primary infection, plays a significant role in down-regulating host pathology.

Impaired host defense, hematopoiesis, granulomatous inflammation and type 1-type 2 cytokine balance in mice lacking CC chemokine receptor 1

CC chemokine receptor 1 (CCR1) is expressed in neutrophils, monocytes, lymphocytes, and eosinophils, and binds the leukocyte chemoattractant and hematopoiesis regulator macrophage inflammatory protein (MIP)-1alpha, as well as several related CC chemokines. Four other CCR subtypes are known; their leukocyte and chemokine specificities overlap with, but are not identical to, CCR1, suggesting that CCR1 has both redundant and specific biologic roles. To test this, we have developed CCR1-deficient mice (-/-) by targeted gene disruption. Although the distribution of mature leukocytes was normal, steady state and induced trafficking and proliferation of myeloid progenitor cells were disordered in -/- mice. Moreover, mature neutrophils from -/- mice failed to chemotax in vitro and failed to mobilize into peripheral blood in vivo in response to MIP-1alpha. Consistent with this, -/- mice had accelerated mortality when challenged with Aspergillus fumigatus, a fungus controlled principally by neutrophils. To test the role of CCR1 in granuloma formation, we injected Schistosoma mansoni eggs intravenously, and observed a 40% reduction in the size of lung granulomas in -/- mice compared to +/+ littermates. This was associated with increased interferon-gamma and decreased interleukin-4 production in -/- versus +/+ lung lymph node cells stimulated with egg-specific antigen, suggesting that CCR1 influences the inflammatory response not only through direct effects on leukocyte chemotaxis, but also through effects on the type 1-type 2 cytokine balance. Thus CCR1 has nonredundant functions in hematopoiesis, host defense, and inflammation.

Schistosoma mansoni: unisexual infections sensitized mice for granuloma formation around intravenously injected eggs

Mice carrying unisexual infection with male or female Schistosoma mansoni for 9 weeks developed accelerated and augmented reactions to S. mansoni eggs injected intravenously. The size of circumoval granulomas observed in the lungs of unisexually infected mice did not differ significantly from the reactions seen in bisexually infected mice. Tissue eosinophilia in the granulomas was also augmented similarly over that in naive mice by unisexual or bisexual infection. The cross-reactivity between worm and egg antigens is relevant to the development of acute toxemic schistosomiasis mansoni and, perhaps, to the consideration of antigens to be used for vaccination against S. mansoni infection.

IL-12 enhances vaccine-induced immunity to schistosomes by augmenting both humoral and cell-mediated immune responses against the parasite

The production of Th1-type cytokines is associated with strong cell-mediated immunity, while Th2-type cytokines typically dominate humoral immune responses. In mice vaccinated a single time with attenuated cercariae of Schistosoma mansoni, the protection induced is associated with Th1 cytokine-dependent, cell-mediated immunity. In contrast, mice vaccinated multiple times display a more Th2-type dominant cytokine response and develop Ab-dependent resistance. We have previously shown that IL-12 enhances cell-mediated immunity in singly vaccinated mice. In the present study, we asked what effects administering IL-12 as an adjuvant would have on the development of a protective humoral response in multiply immunized animals. We found that multiply immunized/IL-12-treated mice displayed a marked increase in resistance to challenge infection, with some animals demonstrating complete protection. The IL-12-vaccinated mice developed strongly polarized Th1 responses but, importantly, also showed significant increases in parasite-specific Ab and, in particular, IgG2a, IgG2b, and IgG1 isotypes. Passive transfer demonstrated an enhanced ability of serum from these animals to protect naive recipients. In addition, animals vaccinated in the presence of IL-12 also developed macrophages with increased nitric oxide-dependent killing activity against the parasites. Together, these data demonstrate that IL-12, initially described as an adjuvant for cell-mediated immunity, may be used to simultaneously to promote both humoral and cell-mediated protective responses against infection.

In the absence of endogenous IFN-gamma, mice develop unimpaired IL-12 responses to Toxoplasma gondii while failing to control acute infection

The relationship between IFN-gamma and IL-12 in generating innate immune responses and resistance to acute Toxoplasma gondii infection was assessed in T. gondii-exposed IFN-gamma knockout (gko) mice. Gko mice, in contrast to wild-type (wt) animals, rapidly succumbed to infection with either the avirulent ME49 strain or, surprisingly, an attenuated temperature-sensitive mutant strain, ts4. Microscopic examination of peritoneal exudates from infected gko mice demonstrated that mortality is associated with unchecked tachyzoite replication. Nevertheless, both wt and gko animals developed a peritoneal inflammatory response that in gko animals was greater due to a 5- to 10-fold increase in the number of granulocytes recruited to the site of infection. In addition, IL-12 production in gko mice was both unimpaired and functional since a significant, albeit lower than wt, IL-12-dependent NK cell response developed in these animals. Regardless, no evidence for an IFN-gamma-independent protective function for IL-12 or NK cells was apparent since in vivo treatment of gko mice with an IL-12-neutralizing mAb ablated the NK cell response, but did not decrease survival. Together, these data identify distinct functions for IL-12 and IFN-gamma in host resistance to T. gondii: IL-12 precedes and initiates synthesis of IFN-gamma, while the latter lymphokine directly controls parasite growth and diminishes the contribution of IL-4- and IL-5-producing T cell subsets.

In the absence of endogenous IFN-gamma, mice develop unimpaired IL-12 responses to Toxoplasma gondii while failing to control acute infection

The relationship between IFN-gamma and IL-12 in generating innate immune responses and resistance to acute Toxoplasma gondii infection was assessed in T. gondii-exposed IFN-gamma knockout (gko) mice. Gko mice, in contrast to wild-type (wt) animals, rapidly succumbed to infection with either the avirulent ME49 strain or, surprisingly, an attenuated temperature-sensitive mutant strain, ts4. Microscopic examination of peritoneal exudates from infected gko mice demonstrated that mortality is associated with unchecked tachyzoite replication. Nevertheless, both wt and gko animals developed a peritoneal inflammatory response that in gko animals was greater due to a 5- to 10-fold increase in the number of granulocytes recruited to the site of infection. In addition, IL-12 production in gko mice was both unimpaired and functional since a significant, albeit lower than wt, IL-12-dependent NK cell response developed in these animals. Regardless, no evidence for an IFN-gamma-independent protective function for IL-12 or NK cells was apparent since in vivo treatment of gko mice with an IL-12-neutralizing mAb ablated the NK cell response, but did not decrease survival. Together, these data identify distinct functions for IL-12 and IFN-gamma in host resistance to T. gondii: IL-12 precedes and initiates synthesis of IFN-gamma, while the latter lymphokine directly controls parasite growth and diminishes the contribution of IL-4- and IL-5-producing T cell subsets.

IL-12 enhances vaccine-induced immunity to schistosomes by augmenting both humoral and cell-mediated immune responses against the parasite

The production of Th1-type cytokines is associated with strong cell-mediated immunity, while Th2-type cytokines typically dominate humoral immune responses. In mice vaccinated a single time with attenuated cercariae of Schistosoma mansoni, the protection induced is associated with Th1 cytokine-dependent, cell-mediated immunity. In contrast, mice vaccinated multiple times display a more Th2-type dominant cytokine response and develop Ab-dependent resistance. We have previously shown that IL-12 enhances cell-mediated immunity in singly vaccinated mice. In the present study, we asked what effects administering IL-12 as an adjuvant would have on the development of a protective humoral response in multiply immunized animals. We found that multiply immunized/IL-12-treated mice displayed a marked increase in resistance to challenge infection, with some animals demonstrating complete protection. The IL-12-vaccinated mice developed strongly polarized Th1 responses but, importantly, also showed significant increases in parasite-specific Ab and, in particular, IgG2a, IgG2b, and IgG1 isotypes. Passive transfer demonstrated an enhanced ability of serum from these animals to protect naive recipients. In addition, animals vaccinated in the presence of IL-12 also developed macrophages with increased nitric oxide-dependent killing activity against the parasites. Together, these data demonstrate that IL-12, initially described as an adjuvant for cell-mediated immunity, may be used to simultaneously to promote both humoral and cell-mediated protective responses against infection.

Development of an antipathology vaccine for schistosomiasis

The data presented here clearly demonstrate that IL-12 can act as an adjuvant, suppressing both granuloma formation and fibrosis induced after natural schistosome infection. Recently, we showed that IL-12 can increase protective immunity provided by an attenuated larval schistosome vaccine as well. In both cases the vaccines appear to suppress in large part the parasite-induced Th2 responses. Thus, the use of cytokines as adjuvants offers a rational approach for immunomodulation when the effector mechanism of a particular vaccine is known. Clearly, IL-12 has enormous potential for modulating the outcome of immunization and may have broad application in preventing a variety of different infectious diseases.

Beta 2-microglobulin-dependent NK1.1+ T cells are not essential for T helper cell 2 immune responses

A number of investigations have established the critical role of interleukin 4 (IL-4) in mediating the development of T helper (Th)2 effector cells in vitro and in vivo. Despite intensive study, the origin of the IL-4 required for Th2 priming and differentiation remains unclear. Natural killer (NK)1.1+ alpha/beta T cell receptor+ T(NT) cells, a unique lineage of cells capable of producing large amounts of IL-4 after activation in vivo, are important candidates for directing Th2 priming. These cells are selected by the nonpolymorphic major histocompatibility complex (MHC) class I molecule, CD1, and are deficient in beta 2-microglobulin (beta 2m)-null mice. We used beta 2m-deficient mice on both BALB/c and C57BL/6 backgrounds to examine their capacity to mount Th2 immune responses after challenge with a number of well-characterized antigens administered by a variety of routes. As assessed by immunization with protein antigen, infection with Leishmania major, embolization with eggs of Schistosoma mansoni, intestinal infection with Nippostrongylus brasiliensis, or induction of airway hyperreactivity to aerosolized antigen, beta 2m-deficient mice developed functional type 2 immune responses that were not substantially different than those in wild-type mice. Production of IL-4 and the generation of immunoglobulin E (IgE) and eosinophil responses were preserved as assessed by a variety of assays. Collectively, these results present a comprehensive analysis of type 2 immune responses in beta 2m-deficient mice, and indicate that beta 2m-dependent NT cells are not required for Th2 development in vivo.

Molecular analysis of decreased interleukin-12 production in persons infected with human immunodeficiency virus

Human immunodeficiency virus (HIV) disease is associated with loss of type 1 responses, including interleukin (IL)-12 production. The dramatic drop in p70 production seen at early stages of disease was found not to be associated with a similarly decreased p40 mRNA expression. p35 mRNA expression was more extensively reduced than p40 mRNA expression at these early stages. Monocytes infected in vitro with HIV displayed decreased p35 expression and p70 production, suggesting that such decreased IL-12 expression may contribute to reduced IL-12 production in HIV-positive patients' cells. In addition, treatment of cells with IL-10 increased IL-10 mRNA expression and decreased p40 expression in both HIV-positive and -negative cells, while neutralization of IL-10 increased p40 mRNA levels. These observations, together with the observed hyperproduction of IL-10 in HIV-positive patients, may explain the dysregulation of IL-12 production seen in HIV disease.

Effect of liposome-mediated macrophage depletion on LPS-induced cytokine gene expression and radioprotection

Tissue-specific cytokine mRNA expression was examined in mice that received LPS. In the liver, IL-6, IL-10, IL-12 (p40), and TNF-alpha were induced by 30 min after injection with LPS. In the spleen, IL-6 and TNF-alpha were induced by 30 min after LPS challenge, while increases in IL-10 and IL-12 (p40) were delayed in onset. GM-CSF, IFN-gamma, and IL-12 (p35) were not induced in the liver or spleen until 60 to 90 min after LPS injection. Mice were depleted of macrophages in their liver and spleen by i.v. injection of liposome-encapsulated dichloromethylene bisphosphonate (Cl2MBP). Induction of IL-1 beta, IL-6, IL-10, and IL-12 (p40) mRNA by LPS was reduced by > 95% in the liver of macrophage-depleted mice, implicating macrophages as the primary producers of these cytokines. Macrophage depletion resulted in a 50 to 75% reduction in TNF-alpha mRNA in the liver. The results from Cl2MBP-liposome-treated mice also suggested that splenic macrophages were the primary producers of LPS-induced IL-1 beta, IL-6, IL-12 (p40), and IL-1 receptor antagonist (IL-1ra) mRNA, but not IL-10 and TNF-alpha mRNA. Mice treated with Cl2MBP-liposomes were more susceptible to ionizing irradiation than control mice, whether or not they were administered a radioprotective dose of LPS. These findings suggest that depletion of liver and splenic macrophages results in a dysregulation of basal and LPS-induced cytokine responses that can be associated with an altered biologic response.

Effect of liposome-mediated macrophage depletion on LPS-induced cytokine gene expression and radioprotection

Tissue-specific cytokine mRNA expression was examined in mice that received LPS. In the liver, IL-6, IL-10, IL-12 (p40), and TNF-alpha were induced by 30 min after injection with LPS. In the spleen, IL-6 and TNF-alpha were induced by 30 min after LPS challenge, while increases in IL-10 and IL-12 (p40) were delayed in onset. GM-CSF, IFN-gamma, and IL-12 (p35) were not induced in the liver or spleen until 60 to 90 min after LPS injection. Mice were depleted of macrophages in their liver and spleen by i.v. injection of liposome-encapsulated dichloromethylene bisphosphonate (Cl2MBP). Induction of IL-1 beta, IL-6, IL-10, and IL-12 (p40) mRNA by LPS was reduced by > 95% in the liver of macrophage-depleted mice, implicating macrophages as the primary producers of these cytokines. Macrophage depletion resulted in a 50 to 75% reduction in TNF-alpha mRNA in the liver. The results from Cl2MBP-liposome-treated mice also suggested that splenic macrophages were the primary producers of LPS-induced IL-1 beta, IL-6, IL-12 (p40), and IL-1 receptor antagonist (IL-1ra) mRNA, but not IL-10 and TNF-alpha mRNA. Mice treated with Cl2MBP-liposomes were more susceptible to ionizing irradiation than control mice, whether or not they were administered a radioprotective dose of LPS. These findings suggest that depletion of liver and splenic macrophages results in a dysregulation of basal and LPS-induced cytokine responses that can be associated with an altered biologic response.

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

The harmful fibrosis which often occurs in the context of infectious disease involves the excessive deposition of connective tissue matrix, particularly collagen, and is mostly resistant to pharmacological and immunological intervention. In schistosomiasis, fibrosis is associated with the granulomatous response to parasite eggs trapped in the liver. We have previously shown that interleukin (IL)-12 administered peritoneally with eggs prevents subsequent pulmonary granuloma formation on intravenous challenge with eggs. Here we show that sensitization with eggs plus IL-12 partly inhibits granuloma formation and dramatically reduces the tissue fibrosis induced by natural infection with Schistosoma mansoni worms. These results are an example of a vaccine against parasites which acts by preventing pathology rather than infection. IL-12 is known to favour the priming of TH1 rather than Th2 cells, and the effects on fibrosis are accompanied by replacement of the Th2-dominated pattern of cytokine expression characteristic of S. mansoni infection with one dominated by Th1 cytokines. Elevated Th2 cytokine expression and fibrosis are common manifestations of a wide variety of infectious diseases and atopic disorders which might be ameliorated by vaccination with antigen and IL-12.

Cytokine regulation of granuloma formation in schistosomiasis

Granuloma induced by the schistosome egg is an inflammatory reaction that is tightly controlled by the interaction of T-helper cell type 1 (Th1) and Th2 cytokines produced locally. Studies focussing on the immunoregulation of the response have yielded numerous insights into the cytokine cascade that controls the formation of the lesions. It is clear from current data that the Th2 cytokines play a primary role in granuloma formation, whereas the Th1-associated lymphokine interferon-gamma acts as an endogenous downregulator of the response. Through recent advances, it may now be possible to design effective cytokine-based vaccination strategies that will suppress the tissue pathology associated with this helminth infection.

Suppressive effect of interleukin-4 neutralization differs for granulomas around Schistosoma mansoni eggs injected into mice compared with those around eggs laid in infected mice

The principal pathological manifestation of murine Schistosoma mansoni infection is the egg-induced granuloma. Synchronous pulmonary granulomas forming around intravenously injected schistosome eggs are widely used to study the immunopathology of schistosomiasis. A number of anticytokine antibody treatments have a remarkable effect in modulating granulomas in this model but little effect on the size of hepatic granulomas around laid eggs during experimental infection. To examine this discrepancy, we examined the effects of anticytokine antibodies on liver and lung granulomas around injected eggs and around eggs laid during infection in both locations. Anti-interleukin-4 (IL-4) treatment greatly reduced the volume of granulomas around eggs injected into the liver via the portal vein and around eggs injected into the lung via the tail vein. On the contrary, granulomas around eggs laid by worms in either the liver or the lung during the course of infection were not significantly decreased in size by anti-IL-4 treatment. Thus, site is not important for the disparate effects of anti-IL-4 in granuloma formation around injected versus laid eggs. This effect is seen in naive and sensitized animals and is most probably due to differences in the quality of injected eggs versus those laid in situ by the worms.

IL-12 enhances vaccine-induced immunity to Schistosoma mansoni in mice and decreases T helper 2 cytokine expression, IgE production, and tissue eosinophilia

Vaccination of mice with radiation-attenuated cercariae of Schistosoma mansoni results in a highly significant but partial protection against challenge infection. This immunity is dependent on CD4+ T cells, and because of its suppression by anti-IFN-gamma, appears to be caused by a Th1 response. Nevertheless, both Th1 and Th2 lymphokines are expressed in vaccinated and challenged mice, and we hypothesized that the expression of the latter group of down-regulatory cytokines may be responsible for the failure to obtain complete protection. Because IL-12 is a key cytokine that suppresses Th2-like responses, we asked whether IL-12 could increase vaccine-induced immunity to S. mansoni. Indeed, administration of IL-12 significantly reduced worm burdens following a challenge infection. IL-12-treated animals displayed a marked increase in pulmonary IFN-gamma and IL-12 p40 mRNA expression, while levels of IL-4, IL-5, and IL-13 were suppressed significantly during the period of vaccination. A marked decrease in serum IgE and tissue eosinophilia, two responses regulated by Th2 cytokines, was also observed. Surprisingly, IL-12-treated/vaccinated mice failed to demonstrate a significant increase in IFN-gamma, TNF-alpha, or nitric oxide synthase mRNA at the time of challenge infection when compared with vaccinated controls, but did, however, display significantly suppressed Th2 cytokine mRNA production. Together, these data demonstrate that exogenous IL-12 regulates Th1/Th2 responses during immunization with irradiated cercariae, and suggest that this cytokine may be used to increase vaccine-induced immunity to S. mansoni.

IL-12 enhances vaccine-induced immunity to Schistosoma mansoni in mice and decreases T helper 2 cytokine expression, IgE production, and tissue eosinophilia

Vaccination of mice with radiation-attenuated cercariae of Schistosoma mansoni results in a highly significant but partial protection against challenge infection. This immunity is dependent on CD4+ T cells, and because of its suppression by anti-IFN-gamma, appears to be caused by a Th1 response. Nevertheless, both Th1 and Th2 lymphokines are expressed in vaccinated and challenged mice, and we hypothesized that the expression of the latter group of down-regulatory cytokines may be responsible for the failure to obtain complete protection. Because IL-12 is a key cytokine that suppresses Th2-like responses, we asked whether IL-12 could increase vaccine-induced immunity to S. mansoni. Indeed, administration of IL-12 significantly reduced worm burdens following a challenge infection. IL-12-treated animals displayed a marked increase in pulmonary IFN-gamma and IL-12 p40 mRNA expression, while levels of IL-4, IL-5, and IL-13 were suppressed significantly during the period of vaccination. A marked decrease in serum IgE and tissue eosinophilia, two responses regulated by Th2 cytokines, was also observed. Surprisingly, IL-12-treated/vaccinated mice failed to demonstrate a significant increase in IFN-gamma, TNF-alpha, or nitric oxide synthase mRNA at the time of challenge infection when compared with vaccinated controls, but did, however, display significantly suppressed Th2 cytokine mRNA production. Together, these data demonstrate that exogenous IL-12 regulates Th1/Th2 responses during immunization with irradiated cercariae, and suggest that this cytokine may be used to increase vaccine-induced immunity to S. mansoni.

IL-12 exacerbates rather than suppresses T helper 2-dependent pathology in the absence of endogenous IFN-gamma

To assess the role of IFN-gamma in the in vivo regulation of Th subset differentiation by IL-12, schistosome egg-induced Th2 responses and granuloma formation were studied in IFN-gamma knock-out (gamma KO) mice in which the absence of endogenous IFN-gamma is assured. Rather than suppressing pathology and eosinophilia as observed in wild-type animals, exogenous IL-12 in egg-injected gamma KO mice exacerbated Th2-dependent granuloma formation while failing to reduce peak tissue eosinophilia. Similarly, instead of inhibiting its production, IL-12 caused a dramatic increase in serum IgE levels in gamma KO animals after egg injection. Although the suppressive effects of IL-12 on Th2 responses were blocked in the absence of IFN-gamma, lymphocyte proliferation and IL-2 production were enhanced, a phenomenon which may underlie the observed exacerbation of egg-induced pathology. These findings formally establish that IL-12 inhibits Th2 development indirectly in vivo through the stimulation of IFN-gamma synthesis. In contrast, its promotion of Th1-associated responses seems to be at least partly a result of the direct action of the cytokine.