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Biomedical subjects

A Sher

Publications and source records attributed to A Sher.

At least 73 records · Page 4Linked to original sources
PubMed1998

Infection of mice lacking the common cytokine receptor gamma-chain (gamma(c)) reveals an unexpected role for CD4+ T lymphocytes in early IFN-gamma-dependent resistance to Toxoplasma gondii.

Mice lacking the common cytokine receptor gamma-chain (gamma(c)) gene exhibit defective development of NK cells and CD8+ T cells and greatly diminished production of IFN-gamma. Because resistance of SCID mice to Toxoplasma gondii requires IL-12-dependent IFN-gamma production by NK cells, we expected that gamma(c)-deficient mice would succumb rapidly to the parasite. Surprisingly, however, most gamma(c)-deficient mice survived the acute phase of T. gondii infection. As in wild-type mice, this resistance required IL-12 and IFN-gamma; nevertheless, whereas wild-type mice depleted of CD4+ T cells survived, anti-CD4+ treated gamma(c)-deficient mice displayed diminished production of IFN-gamma and all succumbed to acute infection. These data not only reveal a role for CD4+ T lymphocytes in IFN-gamma-dependent host defense but also establish SCID and gamma(c)-deficient mice as powerful complementary tools for assessing the function of NK vs CD4+ T cells in immunopathophysiologic responses.

Acute Disease↗
PubMed1998

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.

Animals↗
PubMed1998

Decreased resistance of TNF receptor p55- and p75-deficient mice to chronic toxoplasmosis despite normal activation of inducible nitric oxide synthase in vivo.

The importance of TNF-alpha in host defense to the intracellular parasite, Toxoplasma gondii, was investigated in mice lacking both the p55 and p75 receptors for this cytokine. Upon i.p. infection with the avirulent ME49 strain, knockout mice were capable of limiting acute i.p. infection, but succumbed within 3 to 4 wk to a fulminant necrotizing encephalitis. Receptor-deficient mice harbored higher cyst burdens and exhibited uncontrolled tachyzoite replication in the brain. The lack of TNF receptors did not adversely affect the development of a type 1 IFN-gamma response. In vitro studies with peritoneal macrophages stimulated with IFN-gamma and tachyzoites indicated that under limiting concentrations of IFN-gamma, nitric oxide-mediated toxoplasmastatic activity is TNF-alpha dependent. However, this requirement is overcome by increasing the dose of IFN-gamma. Furthermore, both ex vivo and in vivo studies demonstrated that inducible nitric oxide synthase induction in the peritoneal cavity and brain is unimpaired in receptor-deficient mice. Thus, TNF-dependent immune control of T. gondii expansion in the brain involves an effector function distinct from inducible nitric oxide synthase activation.

Animals↗
PubMed1998

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.

Animals↗
PubMed1998

Helicobacter hepaticus triggers colitis in specific-pathogen-free interleukin-10 (IL-10)-deficient mice through an IL-12- and gamma interferon-dependent mechanism.

Mice rendered deficient in interleukin-10 (IL-10) by gene targeting (IL-10(-/-) mice) develop chronic enterocolitis resembling human inflammatory bowel disease (IBD) when maintained in conventional animal facilities. However, they display a minimal and delayed intestinal inflammatory response when reared under specific-pathogen-free (SPF) conditions, suggesting the involvement of a microbial component in pathogenesis. We show here that experimental infection with a single bacterial agent, Helicobacter hepaticus, induces chronic colitis in SPF-reared IL-10(-/-) mice and that the disease is accompanied by a type 1 cytokine response (gamma interferon [IFN-gamma], tumor necrosis factor alpha, and nitric oxide) detected by restimulation of spleen and mesenteric lymph node cells with a soluble H. hepaticus antigen (Ag) preparation. In contrast, wild-type (WT) animals infected with the same bacteria did not develop disease and produced IL-10 as the dominant cytokine in response to Helicobacter Ag. Strong H. hepaticus-reactive antibody responses as measured by Ag-specific total immunoglobulin G (IgG), IgG1, IgG2a, IgG2b, IgG3, and IgA were observed in both WT and IL-10(-/-) mice. In vivo neutralization of IFN-gamma or IL-12 resulted in a significant reduction of intestinal inflammation in H. hepaticus-infected IL-10(-/-) mice, suggesting an important role for these cytokines in the development of colitis in the model. Taken together, these microbial reconstitution experiments formally establish that a defined bacterial agent can serve as the immunological target in the development of large bowel inflammation in IL-10(-/-) mice and argue that in nonimmunocompromised hosts IL-10 stimulated in response to intestinal flora is important in preventing IBD.

Animals↗
PubMed1998

Partially protective vaccination permits the development of latency in a normally virulent strain of Toxoplasma gondii.

The virulent RH strain of Toxoplasma gondii is acutely lethal in mice and fails to establish chronic infection. Vaccination of BALB/c mice with a soluble tachyzoite antigen preparation, STAg, in combination with the immunostimulatory cytokine interleukin-12 results in partial protection against RH lethal challenge. Nevertheless, brain tissue obtained from surviving, vaccinated mice as late as 1 year after RH infection contained latent parasite forms as demonstrated by subinoculation into naive recipients. The tachyzoites arising in the subinoculated animals were genetically indistinguishable from the original RH inoculum. Microscopic examination revealed that the persistent parasite forms present in the brains of vaccinated and challenged mice have a tissue cyst-like morphology and express the bradyzoite antigen BAG-1 but not the tachyzoite-specific antigen SAG-2 but are different from the cysts formed by avirulent T. gondii strains in that the internal parasite stages display ultrastructural features intermediate between tachyzoites and bradyzoites. Moreover, the zoites within the RH tissue cysts are clearly distinct from conventional bradyzoites in their sensitivity to pepsin-HCl digestion. In contrast to the observations made with partially resistant STAg/interleukin-12-vaccinated animals, no latent forms could be detected in brain tissue after RH challenge of mice immunized with a live attenuated tachyzoite vaccine which confers total protection against this parasite isolate. The above findings demonstrate the potential of a virulent T. gondii strain to generate latent parasite stages, a process which may be promoted under conditions of incomplete vaccination.

Animals↗
PubMed1998

Paclitaxel (Taxol)-induced killing of Leishmania major in murine macrophages.

The antitumor drug paclitaxel (Taxol) has been demonstrated to be a lipopolysaccharide mimetic in murine macrophages. In this study, the capacity of paclitaxel to activate macrophages to become microbicidal for Leishmania major was examined. Paclitaxel and gamma interferon synergized to kill intracellular L. major in Lpsn, but not Lpsd, macrophages by a nitric oxide (NO.)-dependent mechanism.

Animals↗
PubMed1998

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.

Animals↗
PubMed1998

Cytokines as determinants of disease and disease interactions.

The immune response to pathogens results in both host resistance and immunopathology. Cytokines and in particular those lymphokines produced by Th1 and Th2 cells play a key role in determining the balance between these two immunologic outcomes. Recent data suggest that interleukin-10, a product of both Th2 cells and macrophages, protects the host against excessive immunopathology. The cytokine environment generated by different pathogens may also influence the course and outcome of infections with unrelated organisms. This relationship may be particularly important in the case of HIV-1 where prior Th1 or Th2 biases established by helminth or intracellular infections may influence either initial viral susceptibility or drive progression to AIDS through immune activation.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Ignition of the type 1 response to intracellular infection by dendritic cell-derived interleukin-12.

Host resistance to many intracellular pathogens is dependent on the induction of host IFN-gamma. This response in turn is triggered by the critical initiation cytokine, IL-12. Activated macrophages provide a major source of IL-12 during infection yet are unlikely to be the initial cell to produce the cytokine because of their need for IFN-gamma priming and/or other co-stimulatory signals. We have utilized an in vivo approach to identify the primary IL-12 producing cells which respond to the intracellular protozoan Toxoplasma gondii. Our results indicate that in spleen interdigitating dendritic cells (IDC) but not macrophages rapidly synthesize IL-12 after injection of parasite products or live tachyzoites. This response is both IFN-gamma and T lymphocyte independent. The same microbial stimulus results in the migration of IDC precursors into T cell areas and the upregulation of co-stimulatory cell-surface molecules. We postulate that these early dendritic cell activation events represent the "ignition switch" for the subsequent Type 1 cytokine response which leads to control of infection.

Animals↗
PubMed1997

In vivo microbial stimulation induces rapid CD40 ligand-independent production of interleukin 12 by dendritic cells and their redistribution to T cell areas.

The early induction of interleukin (IL)-12 is a critical event in determining the development of both innate resistance and adaptive immunity to many intracellular pathogens. Previous in vitro studies have suggested that the macrophage (MPhi) is a major source of the initial IL-12 produced upon microbial stimulation and that this response promotes the differentiation of protective T helper cell 1 (Th1) CD4+ lymphocytes from precursors that are primed on antigen-bearing dendritic cells (DC). Here, we demonstrate by immunolocalization experiments and flow cytometric analysis that, contrary to expectation, DC and not MPhi are the initial cells to synthesize IL-12 in the spleens of mice exposed in vivo to an extract of Toxoplasma gondii or to lipopolysaccharide, two well characterized microbial stimulants of the cytokine. Importantly, this production of IL-12 occurs very rapidly and is independent of interferon gamma priming or of signals from T cells, such as CD40 ligand. IL-12 production by splenic DC is accompanied by an increase in number of DCs, as well as a redistribution to the T cell areas and the acquisition of markers characteristic of interdigitating dendritic cells. The capacity of splenic DC but not MPhi to synthesize de novo high levels of IL-12 within hours of exposure to microbial products in vivo, as well as the ability of the same stimuli to induce migration of DC to the T cell areas, argues that DC function simultaneously as both antigen-presenting cells and IL-12 producing accessory cells in the initiation of cell-mediated immunity to intracellular pathogens. This model avoids the need to invoke a three-cell interaction for Th1 differentiation and points to the DC as both a sentinel for innate recognition and the dictator of class selection in the subsequent adaptive response.

Animals↗
PubMed1997

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.

Animals↗
PubMed1997

Interferon consensus sequence binding protein-deficient mice display impaired resistance to intracellular infection due to a primary defect in interleukin 12 p40 induction.

Mice lacking the transcription factor interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family of transcription proteins, were infected with the intracellular protozoan, Toxoplasma gondii. ICSBP-deficient mice exhibited unchecked parasite replication in vivo and rapidly succumbed within 14 d after inoculation with an avirulent Toxoplasma strain. In contrast, few intracellular parasites were observed in wild-type littermates and these animals survived for at least 60 d after infection. Analysis of cytokine synthesis in vitro and in vivo revealed a major deficiency in the expression of both interferon (IFN)-gamma and interleukin (IL)-12 p40 in the T. gondii exposed ICSBP-/- animals. In related experiments, macrophages from uninfected ICSBP-/- mice were shown to display a selective impairment in the mRNA expression of IL-12 p40 but not IL-1alpha, IL-1beta, IL-1Ra, IL-6, IL-10, or TNF-alpha in response to live parasites, parasite antigen, lipopolysaccharide, or Staphylococcus aureus. This selective defect in IL-12 p40 production was observed regardless of whether the macrophages had been primed with IFN-gamma. We hypothesize that the impaired synthesis of IL-12 p40 in ICSBP-/- animals is the primary lesion responsible for the loss in resistance to T. gondii because IFN-gamma-induced parasite killing was unimpaired in vitro and, more importantly, administration of exogenous IL-12 in vivo significantly prolonged survival of the infected mice. Together these findings implicate ICSBP as a major transcription factor which directly or indirectly regulates IL-12 p40 gene activation and, as a consequence, IFN-gamma-dependent host resistance.

Acute Disease↗
PubMed1997

Mechanisms of innate resistance to Toxoplasma gondii infection.

The interaction of protozoan parasites with innate host defences is critical in determining the character of the subsequent infection. The initial steps in the encounter of Toxoplasma gondii with the vertebrate immune system provide a striking example of this important aspect of the host-parasite relationship. In immuno-competent individuals this intracellular protozoan produces an asymptomatic chronic infection as part of its strategy for transmission. Nevertheless, T. gondii is inherently a highly virulent pathogen. The rapid induction by the parasite of a potent cell-mediated immune response that both limits its growth and drives conversion to a dormant cyst stage explains this apparent paradox. Studies with gene-deficient mice have demonstrated the interleukin-12 (IL-12)-dependent production of interferon gamma (IFN-gamma) to be of paramount importance in controlling early parasite growth. However, this seems to be independent of nitric oxide production as mice deficient in inducible nitric oxide synthase (iNOS) and tumour necrosis factor receptor were able to control early growth of T. gondii, although, they later succumbed to infection. Nitric oxide does, however, seem to be important in controlling persistent infection; treating chronic infection with iNOS metabolic inhibitors results in disease reactivation. Preliminary evidence implicates neutrophils in effector pathways against this parasite distinct from that described for macrophages. Once initiated, IL-12-dependent IFN-gamma production in synergy with other proinflammatory cytokines can positively feed back on itself to induce 'cytokine shock'. Regulatory cytokines, particularly IL-10, are essential to down-regulate inflammation and limit host pathology.

Animals↗
PubMed1997

Adsorption to aluminum hydroxide promotes the activity of IL-12 as an adjuvant for antibody as well as type 1 cytokine responses to HIV-1 gp120.

A series of protocols were tested to examine the adjuvant effects of IL-12 on humoral and type 1 cytokine responses elicited in mice by recombinant gp120 envelope protein from HIV-1. This Ag fails to induce detectable Ab responses when administered s.c. alone, but stimulates low Ab levels when combined with aluminum hydroxide (alum). Moreover, when i.p. injected rIL-12 was included in the immunization, no increase in Ab production was observed. Importantly, optimal gp120 Ab responses were achieved by immunizing mice s.c. with gp120 and rIL-12 simultaneously coadsorbed to alum. These animals displayed a highly polarized, type 1 cytokine profile, with the emergence of anti-gp120 Ig belonging to the IgG2 and IgG3 isotypes. In addition, a major increase occurred in Ab of the IgG1 subclass. The superior adjuvant activity of alum-adsorbed IL-12 compared with that of the free cytokine correlated with the prolonged detection of IFN-gamma in the sera of animals immunized using the former procedure. In related experiments, in vitro neutralization of IL-12 was shown to inhibit IFN-gamma production by spleen cells from mice immunized with gp120 plus alum, but not by splenocytes from mice primed in the presence of IL-12, suggesting that the latter protocol induces a stable type 1 phenotype. These studies demonstrate that presentation of IL-12 on alum enhances its immunomodulatory effects and establish a protocol for the use of the cytokine as an adjuvant for simultaneously promoting both humoral Ab and type 1 cytokine responses.

AIDS Vaccines↗
PubMed1997

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.

Animals↗