Hai Ning Shi

Concurrent enteric helminth infection modulates inflammation and gastric immune responses and reduces helicobacter-induced gastric atrophy.

Helicobacter pylori is causally associated with gastritis and gastric cancer. Some developing countries with a high prevalence of infection have high gastric cancer rates, whereas in others, these rates are low. The progression of helicobacter-induced gastritis and gastric atrophy mediated by type 1 T-helper cells may be modulated by concurrent parasitic infection. Here, in mice with concurrent helminth infection, helicobacter-associated gastric atrophy was reduced considerably despite chronic inflammation and high helicobacter colonization. This correlated with a substantial reduction in mRNA for cytokines and chemokines associated with a gastric inflammatory response of type 1 T-helper cells. Thus, concurrent enteric helminth infection can attenuate gastric atrophy, a premalignant lesion.

Toll-Like Receptor 4 Signaling by Intestinal Microbes Influences Susceptibility to Food Allergy

The mechanisms by which signaling by the innate immune system controls susceptibility to allergy are poorly understood. In this report, we show that intragastric administration of a food allergen with a mucosal adjuvant induces allergen-specific IgE, elevated plasma histamine levels, and anaphylactic symptoms in three different strains of mice lacking a functional receptor for bacterial LPS (Toll-like receptor 4 (TLR4)), but not in MHC-matched or congenic controls. Susceptibility to allergy correlates with a Th2-biased cytokine response in both the mucosal (mesenteric lymph node and Peyer’s patch) and systemic (spleen) tissues of TLR4-mutant or -deficient mice. TLR4-mutant mice are not inherently impaired in their ability to regulate Th1 cytokine production because they respond to stimulation via TLR9. Coadministration of CpG oligodeoxynucleotides during sensitization of TLR4-mutant mice with allergen plus CT abrogates anaphylactic symptoms and Ag-specific IgE, and results in a Th1-polarized cytokine response. When the composition of the bacterial flora is reduced and altered by antibiotic administration (beginning at 2 wk of age), TLR4 wild-type mice become as susceptible to the induction of allergy as their TLR4-mutant counterparts. Both allergen-specific IgE and Th2 cytokine responses are reduced in antibiotic-treated mice in which the flora has been allowed to repopulate. Taken together, our results suggest that TLR4-dependent signals provided by the intestinal commensal flora inhibit the development of allergic responses to food Ags.

An Enteric Helminth Infection Protects Against an Allergic Response to Dietary Antigen

Although helminths induce a polarized Th2 response they have been shown, in clinical studies, to confer protection against allergies. To elucidate the basis for this paradox, we have examined the influence of an enteric helminth infection on a model of food allergy. Upon Ag challenge, mice fed peanut (PN) extract plus the mucosal adjuvant cholera toxin (CT) produced PN-specific IgE that correlated with systemic anaphylactic symptoms and elevated plasma histamine. PN-specific IgE was not induced in helminth-infected mice fed PN without CT. Moreover, when PN plus CT was fed to helminth-infected mice, both PN-specific IgE and anaphylactic symptoms were greatly diminished. The down-regulation of PN-specific IgE was associated with a marked reduction in the secretion of IL-13 by PN-specific T cells. When helminth-infected PN plus CT-sensitized mice were treated with neutralizing Abs to IL-10, the PN-specific IgE response and anaphylactic symptoms were similar to, or greater than, those seen in mice that receive PN and CT alone. Taken together, these results suggest that helminth-dependent protection against allergic disease involves immunoregulatory mechanisms that block production of allergen-specific IgE.

Anesthetics isoflurane and desflurane differently affect mitochondrial function, learning, and memory

There are approximately 8.5 million Alzheimer disease (AD) patients who need anesthesia and surgery care every year. The inhalation anesthetic isoflurane, but not desflurane, has been shown to induce caspase activation and apoptosis, which are part of AD neuropathogenesis, through the mitochondria‐dependent apoptosis pathway. However, the in vivo relevance, underlying mechanisms, and functional consequences of these findings remain largely to be determined.

Atg16l1 is required for autophagy in intestinal epithelial cells and protection of mice from Salmonella infection

BACKGROUND & AIMS Intestinal epithelial cells aid in mucosal defense by providing a physical barrier against entry of pathogenic bacteria and secreting antimicrobial peptides (AMPs). Autophagy is an important component of immune homeostasis. However, little is known about its role in specific cell types during bacterial infection in vivo. We investigated the role of autophagy in the response of intestinal epithelial and antigen-presenting cells to Salmonella infection in mice. METHODS We generated mice deficient in Atg16l1 in epithelial cells (Atg16l1(f/f) × Villin-cre) or CD11c(+) cells (Atg16l1(f/f) × CD11c-cre); these mice were used to assess cell type-specific antibacterial autophagy. All responses were compared with Atg16l1(f/f) mice (controls). Mice were infected with Salmonella enterica serovar typhimurium; cecum and small-intestine tissues were collected for immunofluorescence, histology, and quantitative reverse-transcription polymerase chain reaction analyses of cytokines and AMPs. Modulators of autophagy were screened to evaluate their effects on antibacterial responses in human epithelial cells. RESULTS Autophagy was induced in small intestine and cecum after infection with S typhimurium, and required Atg16l1. S typhimurium colocalized with microtubule-associated protein 1 light chain 3β (Map1lc3b or LC3) in the intestinal epithelium of control mice but not in Atg16l1(f/f) × Villin-cre mice. Atg16l1(f/f) × Villin-cre mice also had fewer Paneth cells and abnormal granule morphology, leading to reduced expression of AMPs. Consistent with these defective immune responses, Atg16l1(f/f) × Villin-cre mice had increased inflammation and systemic translocation of bacteria compared with control mice. In contrast, we observed few differences between Atg16l1(f/f) × CD11c-cre and control mice. Trifluoperazine promoted autophagy and bacterial clearance in HeLa cells; these effects were reduced upon knockdown of ATG16L1. CONCLUSIONS Atg16l1 regulates autophagy in intestinal epithelial cells and is required for bacterial clearance. It also is required to prevent systemic infection of mice with enteric bacteria.

Attenuated Inflammatory Responses in Hemochromatosis Reveal a Role for Iron in the Regulation of Macrophage Cytokine Translation

Disturbances of iron homeostasis are associated with altered susceptibility to infectious disease, but the underlying molecular mechanisms are poorly understood. To study this phenomenon, we examined innate immunity to oral Salmonella infection in Hfe knockout (Hfe−/−) mice, a model of the human inherited disorder of iron metabolism type I hemochromatosis. Salmonella- and LPS-induced inflammatory responses were attenuated in the mutant animals, with less severe enterocolitis observed in vivo and reduced macrophage TNF-α and IL-6 secretion measured in vitro. The macrophage iron exporter ferroportin (FPN) was up-regulated in the Hfe−/− mice, and correspondingly, intramacrophage iron levels were lowered. Consistent with the functional importance of these changes, the abnormal cytokine production of the mutant macrophages could be reproduced in wild-type cells by iron chelation, and in a macrophage cell line by overexpression of FPN. The results of analyzing specific steps in the biosynthesis of TNF-α and IL-6, including intracellular concentrations, posttranslational stability and transcript levels, were consistent with reduced translation of cytokine mRNAs in Hfe−/− macrophages. Polyribosome profile analysis confirmed that elevated macrophage FPN expression and low intracellular iron impaired the translation of specific inflammatory cytokine transcripts. Our results provide molecular insight into immune function in type I hemochromatosis and other disorders of iron homeostasis, and reveal a novel role for iron in the regulation of the inflammatory response.

The Role of Microbes in Developmental Immunologic Programming

The role of microorganisms in the gastrointestinal tract has undergone significant modification in the past few decades with new observations from clinical, epidemiologic, and basic science research. We now know that the perception of these gut microbes as pathogens or even as commensals is somewhat outdated. It is becoming increasingly clear that the gut microbiome plays an important role in a host of activities including digestion, protection from potentially pathogenic organisms, and the regulation and development of the host immune system. The complex interactions between microbes and host combined with recent clinical observations and epidemiologic trends may point to the convergence of two well-supported (though imperfect) hypotheses: the “hygiene hypothesis” and the “fetal programming hypothesis.” We are beginning to understand that exposure to microbes before conception, during gestation, and in the neonatal period have profound effects on the developing immune system. Recent observations from a variety of fields help support the expansion of the “fetal programming hypothesis” to a host-microbe corollary that microbe-host interactions at critical windows influence the future immune phenotype, the maintenance of immune health, and the development of immune-mediated disease.

Selective modulation of TLR4-activated inflammatory responses by altered iron homeostasis in mice

Mice deficient in the hemochromatosis gene, Hfe, have attenuated inflammatory responses to Salmonella infection associated with decreased macrophage TNF-alpha and IL-6 biosynthesis after exposure to LPS. In this study, we show that the abnormal cytokine production is related to impaired TLR4 signaling. Despite their abnormal response to LPS, Hfe KO macrophages produced amounts of TNF-alpha similar to those in WT cells after TLR2 stimulation. Consistent with this finding, LPS-induced activation of Mal/MyD88-dependent events was normal in the mutant macrophages. However, LPS-induced IFN-beta expression, a TRAM/TRIF-dependent response activated by TLR4, was reduced by Hfe deficiency. This reduction could be replicated in WT macrophages with the use of iron chelators. In contrast, TLR3-activated expression of IFN-beta, a TRIF-dependent response, was normal in Hfe KO macrophages and was unaffected by iron chelation. Our data suggest that low intracellular iron selectively impairs signaling via the TLR4/TRAM/TRIF pathway proximal to TRIF and results in reduced LPS-induced cytokine expression. Furthermore, by mimicking the altered iron metabolism associated with Hfe deficiency, we found that 3 different inhibitors of hepcidin attenuated Salmonella-induced and noninfectious enterocolitis. Thus, manipulation of iron homeostasis could represent a new therapeutic approach to controlling inflammation.

Concurrent infection with an intestinal helminth parasite impairs host resistance to enteric Citrobacter rodentium and enhances Citrobacter-induced colitis in mice.

ABSTRACT Infections with intestinal helminth and bacterial pathogens, such as enteropathogenic Escherichia coli, continue to be a major global health threat for children. To test the hypothesis that intestinal helminth infection may be a risk factor for enteric bacterial infection, a murine model was established by using the intestinal helminth Heligomosomoides polygyrus. To analyze the modulatory effect of a Th2-inducing helminth on the outcome of enteric bacterium Citrobacter rodentium infection, BALB/c and STAT 6 knockout (KO) mice were infected with H. polygyrus, C. rodentium, or both. We found that only BALB/c mice coinfected with H. polygyrus and C. rodentium displayed a marked morbidity and mortality. The enhanced susceptibility to C. rodentium and intestinal injury of coinfected BALB/c mice were shown to be associated with a significant increase in helminth-driven Th2 responses, mucosally and systemically, and correlated with a significant downregulation of protective gamma interferon and with a dramatic upregulation of the proinflammatory tumor necrosis factor alpha response. In addition, C. rodentium-associated colonic pathology in coinfected BALB/c mice was significantly enhanced, whereas bacterial burden was increased and clearance was delayed. In contrast, coinfection in STAT 6 KO mice failed to promote C. rodentium infection or to induce a more severe intestinal inflammation and tissue injury, demonstrating a mechanism by which helminth influences the development of host protective immunity and susceptibility to bacterial infections. We conclude that H. polygyrus coinfection can promote C. rodentium-associated disease and colitis through a STAT 6-mediated immune mechanism.

B Cell Antigen Receptor Signal Strength and Peripheral B Cell Development are Regulated by a 9-O-Acetyl Sialic Acid Esterase

We show that the enzymatic acetylation and deacetylation of a cell surface carbohydrate controls B cell development, signaling, and immunological tolerance. Mice with a mutation in sialate:O-acetyl esterase, an enzyme that specifically removes acetyl moieties from the 9-OH position of α2–6-linked sialic acid, exhibit enhanced B cell receptor (BCR) activation, defects in peripheral B cell development, and spontaneously develop antichromatin autoantibodies and glomerular immune complex deposits. The 9-O-acetylation state of sialic acid regulates the function of CD22, a Siglec that functions in vivo as an inhibitor of BCR signaling. These results describe a novel catalytic regulator of B cell signaling and underscore the crucial role of inhibitory signaling in the maintenance of immunological tolerance in the B lineage.