Cytokine regulation of schistosome-induced granuloma and fibrosis

Schistosomiasis mansoni, a major cause of hepatic fibrosis in many developing countries, triggers a granulomatous inflammatory reaction in response to its eggs that lodge in the liver. The egg antigens are eliminated slowly, and the persistent granulomatous response leads to prolonged matrix synthesis and hepatic fibrosis. In mice, soluble egg antigens (SEA) induce interleukin 4 synthesis, promoting a dominant T helper type 2 lymphocyte accumulation with the release of additional cytokines (IL-5, IL-10), which not only suppress Th1 lymphocyte subset cytokines, but mediate the characteristic pathophysiology. Manipulation of the cytokine profile with antagonists or exogenous cytokine delivery alters the course of the hepatic inflammation and fibrosis. In the evolution of the granulomatous response to the S. mansoni eggs, transforming growth factor beta (TGF-beta) is also produced that may modulate inflammation and regulate fibrogenesis. In TGF-beta 1-gene targeted mutant mice that over-express TGF-beta 1 (TGF-beta 1 transgenics) or in which TGF-beta 1 has been inactivated (TGF-beta 1-/-; null mutation) or partially inactivated (TGF-beta 1+/-; null mutation heterozygotes), the altered production of TGF-beta 1 impacts on S. mansoni granuloma and hepatic fibrosis. In addition to the Th1/Th2 cytokine balance, modulation of TGF-beta 1 may change the outcome of chronic inflammatory fibrotic disease.

Inducible nitric oxide is essential for host control of persistent but not acute infection with the intracellular pathogen Toxoplasma gondii

The induction by IFN-gamma of reactive nitrogen intermediates has been postulated as a major mechanism of host resistance to intracellular pathogens. To formally test this hypothesis in vivo, the course of Toxoplasma gondii infection was assessed in nitric oxide synthase (iNOS)-/- mice. As expected, macrophages from these animals displayed defective microbicidal activity against the parasite in vitro. Nevertheless, in contrast to IFN-gamma-/- or IL-12 p40-/- animals, iNOS-deficient mice survived acute infection and controlled parasite growth at the site of inoculation. This early resistance was ablated by neutralization of IFN-gamma or IL-12 in vivo and markedly diminished by depletion of neutrophils, demonstrating the existence of previously unappreciated NO independent mechanisms operating against the parasite during early infection. By 3-4 wk post infection, however, iNOS knockout mice did succumb to T. gondii. At that stage parasite expansion and pathology were evident in the central nervous system but not the periphery suggesting that the protective role of nitric oxide against this intracellular infection is tissue specific rather than systemic.

Critical roles for the Bcl-3 oncoprotein in T cell-mediated immunity, splenic microarchitecture, and germinal center reactions

Chromosomal translocations of bcl-3 are associated with chronic B cell lymphocytic leukemias. Previously, we have shown that Bcl-3, a distinct member of the I kappa B family, may function as a positive regulator of NF-kappa B activity, although its physiologic roles remained unknown. To uncover these roles, we generated Bcl-3-deficient mice. Mutant mice, but not their littermate controls, succumb to T. gondii owing to failure to mount a protective T helper 1 immune response. Bcl-3-deficient mice are also impaired in germinal center reactions and T-dependent antibody responses to influenza virus. The results reveal critical roles for Bcl-3 in antigen-specific priming of T and B cells. Altered microarchitecture of secondary lymphoid organs in mutant mice, including partial loss of B cells, may underlie the immunologic defects. The implied role of Bcl-3 in maintaining B cells in wild-type mice may related to its oncogenic potential.

Role of natural killer cells in innate resistance to protozoan infections

Natural killer cells are now recognized as major effectors of innate resistance to protozoan parasites. The principal mechanism by which they control the growth of these pathogens is indirect, involving cytokine production rather than cytolytic activity. Recent studies have identified a series of positive and negative signals provided by cytokines and cellular interactions which regulate protozoa-induced natural killer cell function.

Developmental differences determine larval susceptibility to nitric oxide-mediated killing in a murine model of vaccination against Schistosoma mansoni

A persistent paradox in our understanding of protective immunity against Schistosoma mansoni infection in animals vaccinated with attenuated parasites has been that attrition of challenge parasites occurs during migration through the lungs in vivo, although parasites recovered from the lungs appear to be relatively resistant to cytotoxic effector mechanisms in vitro. We have compared the susceptibilities of different stages of larvae to killing by nitric oxide (NO), which was previously shown to be involved in the larvicidal function of cytokine-activated cytotoxic effector cells. Lung-stage larvae obtained 1 week after infection were not killed in vitro by NO generated either by a chemical NO donor or by activated cells. In contrast, parasites obtained from the portal system of control mice or from the lungs of vaccinated mice 2.5 weeks following challenge infection were killed by NO. As previously shown for mammalian cell targets, the effects of NO in susceptible larval stages may involve enzymes required for aerobic energy metabolism, since similar cytotoxicity was demonstrated by chemical inhibitors of the citric acid cycle or mitochondrial respiration. Taken together with previous observations of enhanced Th1 activity and expression of NO synthase in the lungs of vaccinated mice at 2.5 weeks after challenge infection, these observations elucidate the immune mechanism of vaccine-induced resistance to S. mansoni infection. Moreover, they suggest that conversion to a less metabolically active state may allow pathogens to escape the effects of the important effector molecule NO.

Genes for chemokines MuMig and Crg-2 are induced in protozoan and viral infections in response to IFN-gamma with patterns of tissue expression that suggest nonredundant roles in vivo

MuMig and Crg-2 are IFN-inducible murine chemokines whose human homologues, HuMig and IP-10, respectively, share activity in vitro as T cell chemoattractants. We analyzed the expression of the genes Mumig, crg-2, and IFN-gamma during experimental infections with Plasmodium yoelii, Toxoplasma gondii, and vaccinia virus. Mumig, crg-2, and IFN-gamma were induced in multiple organs. During the acute phase of each infection as well as after i.p. injection of rIFN-gamma, levels of Mumig mRNA in the liver were as high or higher than levels in any of the other organs. In contrast, the organs showing the highest expression of crg-2 and IFN-gamma varied among the experimental models, with induction of these latter two genes colocalizing. Differences in relative levels of expression of Mumig and crg-2 in liver and spleen were not demonstrably due to expression of the genes in different cell types within these organs. We showed that both Mumig and crg-2 are induced in the liver in hepatocytes and in the spleen in CD11b+ cells. IFN-gamma was necessary for induction of Mumig during infections with T. gondii or vaccinia virus. In contrast, induction of crg-2 was not completely dependent on IFN-gamma. These data demonstrate that despite the overlap in activities within chemokine subsets, chemokine genes show differences in their patterns of expression and in their responses to inducers that suggest nonredundant roles in vivo. Moreover, the pattern of induction of crg-2 is consistent with Crg-2 acting primarily locally, while the pattern for Mumig induction suggests that MuMig may have a systemic role during infection.

Genes for chemokines MuMig and Crg-2 are induced in protozoan and viral infections in response to IFN-gamma with patterns of tissue expression that suggest nonredundant roles in vivo

MuMig and Crg-2 are IFN-inducible murine chemokines whose human homologues, HuMig and IP-10, respectively, share activity in vitro as T cell chemoattractants. We analyzed the expression of the genes Mumig, crg-2, and IFN-gamma during experimental infections with Plasmodium yoelii, Toxoplasma gondii, and vaccinia virus. Mumig, crg-2, and IFN-gamma were induced in multiple organs. During the acute phase of each infection as well as after i.p. injection of rIFN-gamma, levels of Mumig mRNA in the liver were as high or higher than levels in any of the other organs. In contrast, the organs showing the highest expression of crg-2 and IFN-gamma varied among the experimental models, with induction of these latter two genes colocalizing. Differences in relative levels of expression of Mumig and crg-2 in liver and spleen were not demonstrably due to expression of the genes in different cell types within these organs. We showed that both Mumig and crg-2 are induced in the liver in hepatocytes and in the spleen in CD11b+ cells. IFN-gamma was necessary for induction of Mumig during infections with T. gondii or vaccinia virus. In contrast, induction of crg-2 was not completely dependent on IFN-gamma. These data demonstrate that despite the overlap in activities within chemokine subsets, chemokine genes show differences in their patterns of expression and in their responses to inducers that suggest nonredundant roles in vivo. Moreover, the pattern of induction of crg-2 is consistent with Crg-2 acting primarily locally, while the pattern for Mumig induction suggests that MuMig may have a systemic role during 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.

Toxoplasma gondii: evidence for interleukin-12-dependent and-independent pathways of interferon-gamma production induced by an attenuated parasite strain

Immunity in mice infected with Toxoplasma gondii is dependent upon the ability to generate protective levels of the cytokine IFN-gamma. In this report, we present evidence that the attenuated vaccine strain, ts-4, induces the latter cytokine by both IL-12-dependent and -independent pathways. In contrast, strain ME49 appears to induce IFN-gamma wholly in dependence upon IL-12. Thus, 88% of wildtype C57BL/6 mice treated with anti-IL-12 mAb survive ts-4 infection, unlike similarly treated ME49-infected animals. Moreover, while anti-IL-12 treatment reduced early IFN-gamma and nitric oxide production to background levels in ts-4-infected scid animals, the same treatment in infected C57BL/6 mice had no effect on production of the latter mediators. In addition, we found that anti-IL-12 treatment induces 100% mortality in CD(4+)-deficient MHC class II knockout mice infected with ts-4. Finally, production of nitric oxide (a molecule implicated in parasite control) was abrogated in ts-4-infected scid mice following depletion of IFN-gamma producing NK cells. Together, our results suggest that ts-4 induces IL-12-dependent and -independent IFN-gamma production in normal mice, but ME49 induces the latter cytokine only in dependence upon IL-12. Our data, furthermore, implicate involvement of T cells in the IL-12-independent component of the IFN-gamma response.

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.

Functional diversity of helper T lymphocytes

The existence of subsets of CD4+ helper T lymphocytes that differ in their cytokine secretion patterns and effector functions provides a framework for understanding the heterogeneity of normal and pathological immune responses. Defining the cellular and molecular mechanisms of helper-T-cell differentiation should lead to rational strategies for manipulating immune responses for prophylaxis and therapy.

An IL-12-based vaccine approach for preventing immunopathology in schistosomiasis

Schistosomiasis is a major parasitic disease of developing countries. Pathology in schistosome infection is caused by the host granulomatous response to parasite eggs deposited in the tissues and the ensuing fibrosis. Previous work established that Th2 CD4+ cells play a major role in expanding granulomatous lesions and in fibrosis in murine models. We have used IL-12 both therapeutically to downmodulate this response and as an adjuvant with egg antigens to prevent pathology after subsequent parasite challenge. These effects appears to rely on the induction of IFN-gamma by the injected IL-12. Interestingly, while IL-12 treatment or vaccination downregulates most egg-specific Th2 cytokine responses, IL-10 production in vivo is enhanced. Because we have also shown that IL-12 can be used as an adjuvant to augment protective immunity against this helminth, it may be possible to design a combined parasite Ag/IL-12 vaccine which both limits infection and blocks the tissue pathology caused by eggs of worms escaping the resistance mechanisms evoked by immunization. At a more general level, our results demonstrate the potential of IL-12-based vaccine strategies to block Th2-dependent disease processes including allergy.

Calpain is the target antigen of a Th1 clone that transfers protective immunity against Schistosoma mansoni

A CD4+ clone (clone B), characterized as Th1 based on its selective production of IFN-gamma and IL-2, was established from C57Bl/6 mice protectively immunized against Schistosoma mansoni by intradermal vaccination with soluble worm Ags, plus bacillus Calmette Guerin. In agreement with previous results demonstrating an IFN-gamma-dependent cell-mediated protective mechanism in this vaccination model, Ag-elicited peritoneal macrophages from syngeneic recipients of this clone were activated to kill schistosome larvae (schistosomula) in vitro. Moreover, recipients of clone B displayed significant resistance against cercarial challenge. By screening a battery of lambda(gt11) clones from an adult worm cDNA library, one recombinant (25B) was identified that stimulated clone B specifically. Analysis of the 25B cDNA insert revealed a nucleotide sequence identical with that of the large subunit of schistosome calpain, a Ca2+-activated neutral proteinase. By expressing the products of PCR subcloning, we identified a 146-amino acid region of the 25B gene containing immunologic activity equivalent to the whole polypeptide. Overlapping peptides spanning this region were synthesized, and a core epitope was identified with the sequence EWKGAWCDGS. Since clone B responds to supernatants from cultured schistosomula, we postulate that the recognition of calpain released by invading larvae and resulting induction of Th1 cytokines accounts for the protection mediated by the adoptively transferred clone. Our findings thus implicate calpain as a target of protective immunity in schistosomes and provide the first example of a candidate vaccine Ag for this parasite identified on the basis of T cell reactivity.

Calpain is the target antigen of a Th1 clone that transfers protective immunity against Schistosoma mansoni

A CD4+ clone (clone B), characterized as Th1 based on its selective production of IFN-gamma and IL-2, was established from C57Bl/6 mice protectively immunized against Schistosoma mansoni by intradermal vaccination with soluble worm Ags, plus bacillus Calmette Guerin. In agreement with previous results demonstrating an IFN-gamma-dependent cell-mediated protective mechanism in this vaccination model, Ag-elicited peritoneal macrophages from syngeneic recipients of this clone were activated to kill schistosome larvae (schistosomula) in vitro. Moreover, recipients of clone B displayed significant resistance against cercarial challenge. By screening a battery of lambda(gt11) clones from an adult worm cDNA library, one recombinant (25B) was identified that stimulated clone B specifically. Analysis of the 25B cDNA insert revealed a nucleotide sequence identical with that of the large subunit of schistosome calpain, a Ca2+-activated neutral proteinase. By expressing the products of PCR subcloning, we identified a 146-amino acid region of the 25B gene containing immunologic activity equivalent to the whole polypeptide. Overlapping peptides spanning this region were synthesized, and a core epitope was identified with the sequence EWKGAWCDGS. Since clone B responds to supernatants from cultured schistosomula, we postulate that the recognition of calpain released by invading larvae and resulting induction of Th1 cytokines accounts for the protection mediated by the adoptively transferred clone. Our findings thus implicate calpain as a target of protective immunity in schistosomes and provide the first example of a candidate vaccine Ag for this parasite identified on the basis of T cell reactivity.

In the absence of endogenous IL-10, mice acutely infected with Toxoplasma gondii succumb to a lethal immune response dependent on CD4+ T cells and accompanied by overproduction of IL-12, IFN-gamma and TNF-alpha

To examine the function of IL-10 synthesis during early infection with the intracellular protozoan Toxoplasma gondii, IL-10 knockout (KO) mice were inoculated with an avirulent parasite strain (ME-49). In contrast to control littermates that displayed 100% survival, the IL-10-deficient animals succumbed within the first 2 wk of the infection, with no evidence of enhanced parasite proliferation. The mortality in the IL-10 KO mice was associated with enhanced liver pathology characterized by increased cellular infiltration and intense necrosis. Levels of IL-12 and IFN-gamma in sera of infected IL-10-deficient animals were four- to sixfold higher than those in sera from control mice, as were mRNA levels for IFN-gamma, IL-1 beta, TNF-alpha, and IL-12 in lung tissue. Similarly, macrophages from IL-10 KO mice activated in vitro or in vivo with T. gondii produced higher levels of TNF-alpha and IL-12 than macrophages from control animals. Moreover, spleen cells from IL-10 KO mice infected with T. gondii secreted more IFN-gamma than splenocytes from nondeficient animals. In vitro depletion experiments indicated that CD4+ lymphocytes are the major source of the latter cytokine in the spleen cell populations, and in vivo depletion with anti-CD4 Abs protected the IL-10 KO mice from parasite-induced mortality. Together the data suggest that endogenous IL-10 synthesis plays an important role in vivo in down-regulating monokine and IFN-gamma responses to acute intracellular infection, thereby preventing host immunopathology.

In the absence of endogenous IL-10, mice acutely infected with Toxoplasma gondii succumb to a lethal immune response dependent on CD4+ T cells and accompanied by overproduction of IL-12, IFN-gamma and TNF-alpha

To examine the function of IL-10 synthesis during early infection with the intracellular protozoan Toxoplasma gondii, IL-10 knockout (KO) mice were inoculated with an avirulent parasite strain (ME-49). In contrast to control littermates that displayed 100% survival, the IL-10-deficient animals succumbed within the first 2 wk of the infection, with no evidence of enhanced parasite proliferation. The mortality in the IL-10 KO mice was associated with enhanced liver pathology characterized by increased cellular infiltration and intense necrosis. Levels of IL-12 and IFN-gamma in sera of infected IL-10-deficient animals were four- to sixfold higher than those in sera from control mice, as were mRNA levels for IFN-gamma, IL-1 beta, TNF-alpha, and IL-12 in lung tissue. Similarly, macrophages from IL-10 KO mice activated in vitro or in vivo with T. gondii produced higher levels of TNF-alpha and IL-12 than macrophages from control animals. Moreover, spleen cells from IL-10 KO mice infected with T. gondii secreted more IFN-gamma than splenocytes from nondeficient animals. In vitro depletion experiments indicated that CD4+ lymphocytes are the major source of the latter cytokine in the spleen cell populations, and in vivo depletion with anti-CD4 Abs protected the IL-10 KO mice from parasite-induced mortality. Together the data suggest that endogenous IL-10 synthesis plays an important role in vivo in down-regulating monokine and IFN-gamma responses to acute intracellular infection, thereby preventing host immunopathology.

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.

A role for CD4+ NK1.1+ T lymphocytes as major histocompatibility complex class II independent helper cells in the generation of CD8+ effector function against intracellular infection

Major histocompatibility complex (MHC) class II (A beta) knockout mice were vaccinated with ts-4, an attenuated mutant strain of Toxoplasma gondii, which in normal animals induces strong T cell immunity mediated by interferon gamma (IFN-gamma). After challenge with the lethal parasite strain RH, the knockout mice displayed decreased resistance consistent with absence of CD4+ effectors. Nevertheless, these animals generated CD8+ lymphocyte effectors capable of mediating partial protection through IFN-gamma secretion. Moreover, in vivo neutralization experiments indicated that the development of resistance in knockout mice depends on CD4+ cells as well as interleukin 2 (IL-2). The identity of the IL-2-producing protective cell population was further characterized as CD4+, NK1.1+ by in vitro depletion studies and reverse transcriptase-PCR analysis of fluorescence-activated cell sorter (FACS)-purified CD4+ NK1.1+ T lymphocytes. These results demonstrate that in the absence of conventional MHC class II-restricted CD4+ T lymphocytes, CD8 priming persists and mediates partial protective immunity to T. gondii. Moreover, the data argue that CD4+, NK1.1+ cells, previously implicated in the initiation of T helper cell 2 (Th2) responses through their production of IL-4, can also play a role as alternative IL-2-secreting helper cells in Th1-mediated host resistance to infection.

Biochemical characterization and protein kinase C dependency of monokine-inducing activities of Toxoplasma gondii

Previous reports have indicated that the early induction of interleukin-12 (IL-12), tumor necrosis factor alpha (TNF-alpha), IL-1beta, and IL-10 is crucial for the establishment and regulation of host cell-mediated immunity to the intracellular protozoan parasite Toxoplasma gondii. In this study, we demonstrate that a soluble tachyzoite extract (soluble tachyzoite antigen) can trigger the expression of these four monokines by murine inflammatory macrophages. Further characterization revealed that the parasite molecules in soluble tachyzoite antigen responsible for monokine induction are heat stable at 100 degree C but differ in sensitivity to protease digestion. Thus, the tachyzoite factors that stimulate TNF-alpha and IL-to expression were found to be more resistant to treatment with proteinase K than those responsible for IL-12 and IL-10 induction. Similarly, while the factors responsible for the induction of all four monokines were found to be sensitive to periodate oxidation, the TNF-alpha-stimulating activity was partially resistant to treatment with the compound at a low concentration (1 mM). A further dichotomy in monokine induction signals was inferred from experiments with isoquinoline sulfonamide protein kinase inhibitors. The latter work suggested that the pathways for TNF-alpha and IL-1beta are protein kinase C dependent, while expression of IL-12 and expression of IL-10 share distinct signal transduction mechanisms involving other kinases. Together, these data argue that monokine induction by T. gondii is mediated by glycoproteins that may belong to distinct groups in terms of their biochemical properties and intracellular signaling pathways.

Infection of human immunodeficiency virus 1 transgenic mice with Toxoplasma gondii stimulates proviral transcription in macrophages in vivo

Human immunodeficiency virus (HIV) 1 transgenic mice expressing low or undetectable levels of viral mRNA in lymphoid tissue were infected with the intracellular protozoan Toxoplasma gondii. Exposure to this parasite resulted in an increase in HIV-1 transcript in lymph nodes, spleens, and lungs during the acute phase of infection and in the central nervous system during the chronic stage of disease. In vivo and ex vivo experiments identified macrophages as a major source of the induced HIV-1 transcripts. In contrast, T. gondii infection failed to stimulate HIV-1 transcription in tissues of two HIV-1 transgenic mouse strains harboring a HIV-1 proviral DNA in which the nuclear factor (NF) kappa B binding motifs from the viral long terminal repeats had been replaced with a duplicated Moloney murine leukemia virus core enhancer. A role for NF-kappaB in the activation of the HIV-1 by T. gondii was also suggested by the simultaneous induction of NF-kappaB binding activity and tumor necrosis factor alpha synthesis in transgenic mouse macrophages stimulated by exposure to parasite extracts. These results demonstrate the potential of an opportunistic pathogen to induce HIV-1 transcription in vivo and suggest a mechanism for the in vivo dissemination of HIV-1 by macrophages.

T cell-derived IL-3 induces the production of IL-4 by non-B, non-T cells to amplify the Th2-cytokine response to a non-parasite antigen in Schistosoma mansoni-infected mice

We describe a novel amplification mechanism underlying the increased early IL-4 production observed in Schistosoma mansoni-infected mice in response to a non-parasite Ag, sperm whale myoglobin (SwMb). Earlier studies have shown that splenic Fc epsilon R+ non-B, non-T (NBNT) cells from schistosome-infected mice secrete IL-4 after stimulation with parasite Ag. We now demonstrate that purified NBNT cells from SwMb-immunized S. mansoni-infected mice do not respond directly to SwMb, but produce IL-4 in response to IL-3. Accordingly, we show that the early SwMb-specific IL-4 response of spleen cells (SC) from immunized infected mice is dependent on IL-3 and on CD4+ T cells. Thus, most of the early SwMb-induced IL-4 from SC of infected mice appears to be produced by NBNT cells triggered by IL-3 synthesized by SwMb-specific CD4+ T cells. IL-3-induced IL-4 production was also observed in purified NBNT cells from immunized uninfected mice, but the frequency and/or IL-4-producing capacity of splenic IL-3-responsive cells was found to be 8 to 16 times higher in immunized infected animals. IL-4 production by purified CD4+ cells from immunized infected mice was also seen after SwMb stimulation, but this response showed slower kinetics than those of total SC, was IL-3-independent, and on average threefold greater than that by CD4+ cells from immunized uninfected controls. Thus, increased SwMb-induced IL-4 production in immunized S. mansoni-infected mice results from direct synthesis by CD4+ T cells, as well as their stimulation via IL-3 of an expanded population of NBNT cells. The latter pathway may serve as an amplification loop for Th2-cytokine responses.

T cell-derived IL-3 induces the production of IL-4 by non-B, non-T cells to amplify the Th2-cytokine response to a non-parasite antigen in Schistosoma mansoni-infected mice

We describe a novel amplification mechanism underlying the increased early IL-4 production observed in Schistosoma mansoni-infected mice in response to a non-parasite Ag, sperm whale myoglobin (SwMb). Earlier studies have shown that splenic Fc epsilon R+ non-B, non-T (NBNT) cells from schistosome-infected mice secrete IL-4 after stimulation with parasite Ag. We now demonstrate that purified NBNT cells from SwMb-immunized S. mansoni-infected mice do not respond directly to SwMb, but produce IL-4 in response to IL-3. Accordingly, we show that the early SwMb-specific IL-4 response of spleen cells (SC) from immunized infected mice is dependent on IL-3 and on CD4+ T cells. Thus, most of the early SwMb-induced IL-4 from SC of infected mice appears to be produced by NBNT cells triggered by IL-3 synthesized by SwMb-specific CD4+ T cells. IL-3-induced IL-4 production was also observed in purified NBNT cells from immunized uninfected mice, but the frequency and/or IL-4-producing capacity of splenic IL-3-responsive cells was found to be 8 to 16 times higher in immunized infected animals. IL-4 production by purified CD4+ cells from immunized infected mice was also seen after SwMb stimulation, but this response showed slower kinetics than those of total SC, was IL-3-independent, and on average threefold greater than that by CD4+ cells from immunized uninfected controls. Thus, increased SwMb-induced IL-4 production in immunized S. mansoni-infected mice results from direct synthesis by CD4+ T cells, as well as their stimulation via IL-3 of an expanded population of NBNT cells. The latter pathway may serve as an amplification loop for Th2-cytokine responses.