Interferon-gamma plays a critical role in intestinal immunity against Salmonella typhimurium infection

Salmonella bacteria are a major cause of food-borne infectious diarrhoea and there is great interest in understanding the pathogenesis of Salmonella infection and in vaccine development. Potential vaccines include the aromatic mutants of S. typhimurium. Such non-lethal Aro mutants have also been useful for studying Salmonella infections in mouse models. Studies of systemic infection, using these Aro mutants, in both normal and cytokine gene knockout mice, indicate that interferon-gamma (IFN-gamma) plays a key role in the resolution of Salmonella infection. The present studies have investigated the outcome of oral infection in mice with attenuated Salmonella because this infection route mimics natural infection in humans. In IFN-gamma gene knockout (IFN-gamma-/-) mice, intestinal immunity was impaired and oral challenge resulted in disseminated septicaemia 2 weeks later. No dissemination of infection was seen in wild-type mice. In wild-type mice, both CD4 and CD8 cell numbers increased in the gut following Salmonella challenge, together with increased expression of major histocompatibility complex (MHC) II and vascular cell adhesion molecule-1 (VCAM-1). No such changes were seen in IFNgamma-/- mice. Following oral challenge, antilipopolysaccharide (LPS) and antiphosphoryl choline antibodies increased by more than 100-fold in both serum and faecal pellet extracts of IFNgamma-/- mice compared with wild-type mice. Our data show that IFN-gamma production is essential for resolution of enteric Salmonella infection and that antibody has little effect on this process.     

CD28 costimulation is critical for experimental allergic asthma in HLA-DQ8 transgenic mice

The objective of this study was to investigate the contribution of the CD28 costimulatory molecules to allergen-induced primary and chronic inflammatory responses. To this end, we have developed and characterized a short ragweed allergen-induced asthma model involving sensitization of HLA-DQ transgenic mice followed by intranasal challenge with allergen. Forty-eight hours after primary challenge, sensitized DQ8 mice developed pulmonary eosinophilic inflammation, airway hyperreactivity, Th2 cytokines, and IgE/IgG1 Ab. This allergic inflammatory response was absent in H-2Abeta(0) and DQ8/CD28(0) mice. Secondary rechallenge with allergen 4 weeks later induced even greater inflammatory changes in the airways of DQ8 mice with eosinophils being the predominant inflammatory cells while only pulmonary lymphocytosis was observed in DQ8/CD28(0) mice. No inflammation was detected in H-2Abeta(0) mice. Proliferation and cytokine profile studies demonstrated that CD28 regulates T-cell activation and effector function. Therefore, CD28 is essential for the extrinsic asthma and can be a target for immunotherapy.     

NLRP3 inflammasome pathway has a critical role in the host immunity against clinically relevant Acinetobacter baumannii pulmonary infection

The opportunistic Gram-negative bacterium Acinetobacter baumannii (AB) is a leading cause of life-threatening nosocomial pneumonia. Outbreaks of multidrug resistant (MDR)-AB belonging to international clones (ICs) I and II with limited treatment options are major global health threats. However, the pathogenesis mechanisms of various AB clonal groups are understudied. Although inflammation-associated interleukin-1β (IL-1β) levels and IL-1 receptor antagonist polymorphisms were previously implicated in MDR-AB-related pneumonia in patients, whether inflammasomes has any role in the host defense and/or pathogenesis of clinically relevant A. baumannii infection is unknown. Using a sublethal mouse pneumonia model, we demonstrate that an extensively drug-resistant clinical isolate (ICII) of A. baumannii exhibits reduced/delayed early pulmonary neutrophil recruitment, higher lung persistence, and, most importantly, elicits enhanced IL-1β/IL-18 production and lung damage through NLRP3 inflammasome, in comparison with A. baumannii-type strain. A. baumannii infection-induced IL-1β/IL-18 production is entirely dependent on NLRP3-ASC-caspase-1/caspase-11 pathway. Using Nlrp3^−/− mice infection models, we further show that while NLRP3 inflammasome pathway contributes to host defense against A. baumannii clinical isolate, it is dispensable for protection against A. baumannii-type strain. Our study reveals a novel differential role for NLRP3 inflammasome pathway in the immunity against clinically relevant A. baumannii infections, and highlights inflammasome pathway as a potential immunomodulatory target.     

Mouse peptidoglycan recognition protein PGLYRP-1 plays a role in the host innate immune response against Listeria monocytogenes infection

The role of mouse peptidoglycan recognition protein PGLYRP-1 in innate immunity against Listeria monocytogenes infection was studied. The recombinant mouse PGLYRP-1 and a polyclonal antibody specific to PGLYRP-1 were prepared. The mouse PGLYRP-1 showed antibacterial activities against L. monocytogenes and other Gram-positive bacteria. PGLYRP-1 mRNA expression was induced in the spleens and livers of mice infected with L. monocytogenes. The viable bacterial number increased, and the production of cytokines such as gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) was reduced in mice when mice had been injected with anti-PGLYRP-1 antibody before infection. The levels of IFN-γ and TNF-α titers in the organs were higher and the viable bacterial number was reduced in mice injected with recombinant mouse PGLYRP-1 (rmPGLYRP-1) before infection. PGLYRP-1 could directly induce these cytokines in spleen cell cultures. The elimination of intracellular bacteria was upregulated in NMuLi hepatocyte cells overexpressing PGLYRP-1. The enhancement of the elimination of L. monocytogenes from the organs was observed in IFN-γ(-/-) mice by rmPGLYRP-1 administration but not in TNF-α(-/-) mice. These results suggest that PGLYRP-1 plays a role in innate immunity against L. monocytogenes infection by inducing TNF-α.     

Caveolin-1 plays a critical role in host immunity against Klebsiella pneumoniae by regulating STAT5 and Akt activity

Caveolin-1 (Cav1) is a structural protein of caveolae. Although Cav1 is associated with certain bacterial infections, it is unknown whether Cav1 is involved in host immunity against Klebsiella pneumoniae, the third most commonly isolated microorganism from bacterial sepsis patients. Here, we showed that cav1 knockout mice succumbed to K. pneumoniae infection with markedly decreased survival rates, increased bacterial burdens, intensified tissue injury, hyperactive proinflammatory cytokines, and systemic bacterial dissemination as compared with WT mice. Knocking down Cav1 by a dominant negative approach in lung epithelial MLE-12 cells resulted in similar outcomes (decreased bacterial clearance and increased proinflammatory cytokine production). Furthermore, we revealed that STAT5 influences the GSK3β-β-catenin-Akt pathway, which contributes to the intensive inflammatory response and rapid infection dissemination seen in Cav1 deficiency. Collectively, our findings indicate that Cav1 may offer resistance to K. pneumoniae infection, by affecting both systemic and local production of proinflammatory cytokines via the actions of STAT5 and the GSK3β-β-catenin-Akt pathway.     

Interleukin-12: A bridge between innate resistance and adaptive immunity with a role in infection and acquired immunodeficiency

Interleukin-12 (IL-12) is a disulfide-linked heterodimeric cytokine originally identified as a product of EBV-transformed B cell lines. Monocyte/macrophages are the physiologically most relevant producers of IL-12, in response to both Gram-positive and -negative bacteria, bacterial products, and intracellular parasites. Although IL-12 has an enhancing effect on the survival and growth of early hematopoietic progenitor cells, most of the IL-12 biological activity has been described on T and NK cells, on which it induces production of lymphokines, primarily IFN-, enhances cytotoxic activity, and, in cooperation with other stimuli, increases proliferation. IL-12 is an inducer of development of T helper type 1 (Th-1) cells and the equilibrium between IL-12 and IL-4 is probably important for the balancein vivo between Th-1 and Th-2 responses. IL-12 has an important role in the host resistance to infection, in particular to intracellular pathogens, by activating macrophages through induction of IFN- from NK and T cells and by enhancing cell-mediated immune responses, dependent on Th-1 cell development. Peripheral blood mononuclear cells from HIV-seropositive individuals are impaired in their ability to produce IL-12 in response to bacterial stimulation, and IL-12 restoresin vitro some of the depressed immunological functions, suggesting that a defect in IL-12 production may have a pathogenic role in the immunodeficiency of HIV-infected individuals. Natural IL-12 appears to provide a regulatory link between innate resistance and the development of the antigen-specific adaptive immune response and the recombinant protein has therapeutic potential because of its activity against tumors and infections and its effectiveness as an adjuvant enhancing cell-mediated immunity in vaccination.     

Essential role of Rip2 in the modulation of innate and adaptive immunity triggered by Nod1 and Nod2 ligands

Muramyl peptides are the building blocks of bacterial peptidoglycan, and their biological functions in mammals have been extensively studied. In particular, muramyl peptides trigger inflammation, contribute to host defense against microbial infections, and modulate the adaptive immune response to antigens. These bacterial molecules are detected by nucleotide oligomerization domain 1 (Nod1) and Nod2, and recent evidence suggests that muramyl dipeptide also activates NLRP3 and NLRP1 inflammasomes. Here, we investigated the role of Rip2, the adaptor for Nod1- and Nod2-dependent signaling, in multiple aspects of the host response to muramyl peptides in vivo, such as inflammatory cytokine secretion, activation and recruitment of macrophages and neutrophils to the site of injection, systemic activation of myeloid, T and B cells in the spleen, adjuvanticity and capacity to polarize the adaptive response to ovalbumin. Our results demonstrate that Rip2 was crucial for all the biological functions studied. We also identified CD11c(int) CD11b(+) inflammatory dendritic cells as a major myeloid cell population responding to Nod stimulation in vivo. Together, our results highlight the importance of Rip2 for Nod-dependent induction of innate and adaptive immunity.     

Interleukin 1 plays a major role in the development of Th2-mediated immunity

Expulsion of the gastrointestinal nematode Trichuris muris is mediated by a T helper (Th)2-type response, involving interleukin (IL)-4, IL-9 and IL-13. Here, we show that Th2 response-associated resistance is dependent on the presence of IL-1alpha and IL-1beta. When lymph node cells from naive IL-1alpha- or IL-1beta-deficient mice were subjected to Th2 polarization in vitro, they failed to polarize in the presence of IL-4 alone, but required the addition of exogenous IL-1alpha or IL-1beta. Furthermore, we demonstrate that both IL-1alpha- and IL-1beta-deficient mice are susceptible to chronic T. muris infection and that the inability to expel the worms is associated with a defect in the development of a Th2 response in the mesenteric lymph nodes. These results provide the first demonstration of the critical role of IL-1 in regulating Th2 responses during gastrointestinal nematode infection.     

The role of sex hormones in the development of Th2 immunity in a gender‐biased model of Trichuris muris infection

Trichuris muris infection is an ideal model for defining T‐cell‐driven immunity, and also provides essential insights that may impact on potential helminth therapies currently in development. Conflicting host variables determine the efficiency of such treatments and we have identified host‐derived sex steroid hormones as key factors in the development of immunity. The female‐associated hormone 17‐β estradiol (E2) significantly enhanced the generation of a Th2 response in vitro; however, this stimulatory effect was found to be dispensable for the generation of immunity to Trichuris in the gender‐biased IL‐4KO mouse model. In contrast, the male‐associated hormone dihydrotestosterone significantly inhibited the T‐cell stimulatory capacity of DC and directly suppressed the immune response of male IL‐4KO mice, with worm expulsion restored following castration. This finding was associated with dramatically reduced IL‐18 mRNA expression suggesting androgens may act via this cytokine to suppress Th2 immunity to Trichuris. This study has critical implications for the development and efficacy of potential helminth therapeutics and identifies host gender – specifically sex hormones – as important factors in the development of Th2 immunity in susceptible and immunocompromised mice.     

CD4(+) v(alpha)14 NKT cells play a crucial role in an early stage of protective immunity against infection with Leishmania major

The roles of gamma delta T, NK and NKT cells in an early stage of protective immunity against infection with Leishmania major were investigated. Further, the contribution of these innate cells to the expression of 65 kDa heat shock protein (HSP65) in host macrophages was examined, since we found previously that this expression prevents apoptotic death of infected macrophages and is a crucial step in the acquisition of protective immunity against infection with various obligate intracellular protozoa including L. major. C57BL/6 and DBA/2 mice were found to be resistant against the infection on the basis of the parasite burden in their regional lymph nodes, and to strongly express HSP65 in their macrophages, whereas BALB/c mice were susceptible and barely expressed the HSP65. In those resistant mice, CD4(+) NKT cells prominently increased in their regional lymph node and were the main effector cells at least for an early stage of the protective immunity and for the HSP65 expression, whereas this subset did not increase in susceptible BALB/c mice. Further, neither gamma delta T nor NK cells in resistant mice contributed to those protective immune responses. The NKT cell subset bore CD3, CD4, TCR alpha beta, IL-2R beta and NK1.1 but scarcely asialo-GM(1). Moreover, this effector subset was confirmed to be V(alpha)14 NKT cells by using J(alpha)281(-/-) mice.     

Exacerbated Th2-mediated airway inflammation and hyperresponsiveness in autoimmune diabetes-prone NOD mice: a critical role for CD1d-dependent NKT cells

The NOD mouse has proved to be a relevant model of insulin-dependent diabetes mellitus, closely resembling the human disease. However, it is unknown whether this strain presents a general biastoward Th1-mediated autoimmunity or remains capable of mounting complete Th2-mediated responses. Here, we show that NOD mice have the capacity to develop a typical Th2-mediated disease, namely experimental allergic asthma. In contrast to what might have been expected, they even developed a stronger Th2-mediated pulmonary inflammatory response than BALB/c mice, a strain that shows a typical Th2 bias in this model. Thus, after allergen sensitization and intra-nasal challenge, the typical features of experimental asthma were exacerbated in NOD mice, including enhanced bronchopulmonary responsiveness, mucus production and eosinophilic inflammation in the lungs as well as specific IgE titers in serum. These hallmarks of allergic asthma were associated with increased IL-4, IL-5, IL-13 and eotaxin production in the lungs, as compared with BALB/c mice. Notwithstanding their quantitative and functional defect in NOD mice, CD1d-dependent NKT cells contribute to aggravate the disease, since in OVA-immunized CD1d(-/-) NOD mice, which are deficient in this particular T cell subset, airway eosinophilia was clearly diminished relative to NOD littermates. This is the first evidence that autoimmune diabetes-prone NOD mice can also give rise to enhanced Th2-mediated responses and might thus provide a useful model for the study of common genetic and cellular components, including NKT cells that contribute to both asthma and type 1 diabetes.