Andrew B. Shreiner

The gut microbiome in health and in disease.

Purpose of review Recent technological advancements and expanded efforts have led to a tremendous growth in the collective knowledge of the human microbiome. This review will highlight some of the important recent findings in this area of research. Recent findings Studies have described the structure and functional capacity of the bacterial microbiome in the healthy state and in a variety of disease states. Downstream analyses of the functional interactions between the host and its microbiome are starting to provide mechanistic insights into these interactions. These data are anticipated to lead to new opportunities for diagnosis, prognosis, and treatment of a variety of human diseases. Summary There is a fast growing collection of data describing the structure and functional capacity of the microbiome in a variety of conditions available to the research community for consideration and further exploration. Ongoing efforts to further characterize the functions of the microbiome and the mechanisms underlying host–microbe interactions will provide a better understanding of the role of the microbiome in health and disease.

Anti-CD137 Monoclonal Antibody Administration Augments the Antitumor Efficacy of Dendritic Cell-Based Vaccines

In weakly and poorly immunogenic tumor models, we examined the effects of stimulating CD137 (4-1BB) in vivo by administering anti-CD137 monoclonal antibody after tumor lysate-pulsed dendritic cell (TP-DC) vaccination. TP-DC subcutaneous vaccination induced a transient up-regulation of CD137 on T cells and natural killer (NK) cells within vaccine-primed lymph nodes (VPLNs). In established pulmonary and subcutaneous tumor models, anti-CD137 synergistically enhanced tumor regression after TP-DC vaccination. In the subcutaneous tumor model, the combined therapy resulted in improved survival. Combined therapy also resulted in improved local control of subcutaneous tumor after surgical resection. Anti-CD137 polarized the cytokine release of VPLNs and spleen cells in response to tumor antigen toward a type 1 (interferon-γ) versus a type 2 (interleukin-4) profile. Cell depletion and the use of knockout animals identified that CD8+, CD4+, and NK cells were involved in the tumor rejection response and that CD8+ cells had the major effector role. Anti-CD137 administration resulted in increased proliferation of adoptively transferred OT-1 CD8+ T cells in the VPLNs of mice inoculated with B16-OVA TP-DCs. Polarization toward type 1 (interferon-γ) versus type 2 (interleukin-4) was also observed with the OT-1 cells from VPLNs and spleen cells after anti-CD137 injections. This polarization effect was abrogated by the in vivo depletion of NK cells. These findings indicate that the adjuvant effect of anti-CD137 given in conjunction with TP-DC vaccination is associated with the polarization of T effector cells toward a type 1 response to tumor antigen and is mediated via NK cells.

Coevolution of TH1, TH2, and TH17 Responses during Repeated Pulmonary Exposure to Aspergillus fumigatus Conidia

ABSTRACT Aspergillus fumigatus, a ubiquitous airborne fungus, can cause invasive infection in immunocompromised individuals but also triggers allergic bronchopulmonary aspergillosis in a subset of otherwise healthy individuals repeatedly exposed to the organism. This study addresses a critical gap in our understanding of the immunoregulation in response to repeated exposure to A. fumigatus conidia. C57BL/6 mice were challenged intranasally with A. fumigatus conidia weekly, and leukocyte composition, activation, and cytokine production were examined after two, four, and eight challenges. Approximately 99% of A. fumigatus conidia were cleared within 24 h after inoculation, and repeated exposure to A. fumigatus conidia did not result in hyphal growth or accumulation of conidia with time. After 2 challenges, there was an early influx of neutrophils and regulatory T (Treg) cells into the lungs but minimal inflammation. Repeated exposure promoted sustained expansion of the draining lymph nodes, while the influx of eosinophils and other myeloid cells into the lungs peaked after four exposures and then decreased despite continued A. fumigatus challenges. Goblet cell metaplasia and low-level fibrosis were evident during the response. Repeated exposure to A. fumigatus conidia induced T cell activation in the lungs and the codevelopment by four exposures of TH1, TH2, and TH17 responses in the lungs, which were maintained through eight exposures. Changes in CD4 T cell polarization or Treg numbers did not account for the reduction in myeloid cell numbers later in the response, suggesting a non-T-cell regulatory pathway involved in dampening inflammation during repeated exposure to A. fumigatus conidia.

Tumor-Induced Immune Suppression of In vivo Effector T-Cell Priming Is Mediated by the B7-H1/PD-1 Axis and Transforming Growth Factor β

We have generated effector T cells from tumor-draining lymph nodes (TDLN) that are efficacious in adoptive immunotherapy. We now examine the effect of concomitant tumors on the generation of effector T cells. We inoculated methylcholanthrene (MCA) 205 in the flanks of normal mice and mice bearing MCA 205 lung metastases. TDLN cells from these mice were activated and expanded in vitro, and adoptively transferred to mice bearing lung metastases. Effector T cells generated from TDLN in mice with only flank tumor mediated potent antitumor activity. However, antitumor efficacy of the effector T cells generated from TDLN in mice with pre-existent lung tumor (cTDLN) was reduced. Phenotyping studies showed that dendritic cells in cTDLN expressed higher levels of B7-H1, whereas cTDLN T cells expressed higher levels of PD-1. The levels of IFNgamma were reduced, and the levels of CD4(+)Foxp3(+) regulatory T cells were increased in cTDLN versus TDLN. The in vitro activation of cTDLN was increased by blocking B7-H1 or transforming growth factor (TGF)-beta. Importantly, we found a synergistic up-regulation of IFNgamma with simultaneous blockade of B7-H1 and TGF-beta that was much greater than observed with TDLN. In vitro activation of cTDLN with anti-B7-H1 and anti-TGF-beta and in vivo administration of these antibodies after adoptive transfer resulted in the abrogation of the suppression associated with cTDLN. These results show a major role for the B7-H1/PD-1 axis and TGF-beta as synergistic suppressive mechanisms in cTDLN. Our data have clinical relevance in the generation of effector T cells in the tumor-bearing host.

Interleukin-17 Drives Pulmonary Eosinophilia following Repeated Exposure to Aspergillus fumigatus Conidia

ABSTRACT Previous research in our laboratory has demonstrated that repeated intranasal exposure to Aspergillus fumigatus conidia in C57BL/6 mice results in a chronic pulmonary inflammatory response that reaches its maximal level after four challenges. The inflammatory response is characterized by eosinophilia, goblet cell metaplasia, and T helper TH2 cytokine production, which is accompanied by sustained interleukin-17 (IL-17) expression that persists even after the TH2 response has begun to resolve. TH17 cells could develop in mice deficient in gamma interferon (IFN-γ), IL-4, or IL-10. In the lungs of IL-17 knockout mice repeatedly challenged with A. fumigatus conidia, inflammation was attenuated (with the most significant decrease occurring in eosinophils), conidial clearance was enhanced, and the early transient peak of CD4+ CD25+ FoxP3+ cells blunted. IL-17 appeared to play only a minor role in eosinophil differentiation in the bone marrow but a central role in eosinophil extravasation from the blood into the lungs. These observations point to an expanded role for IL-17 in driving TH2-type inflammation to repeated inhalation of fungal conidia.

Loss of Na+ channel β2 subunits is neuroprotective in a mouse model of Multiple Sclerosis

Multiple sclerosis (MS) is a CNS disease that includes demyelination and axonal degeneration. Voltage-gated Na+ channels are abnormally expressed and distributed in MS and its animal model, Experimental Allergic Encephalomyelitis (EAE). Up-regulation of Na+ channels along demyelinated axons is proposed to lead to axonal loss in MS/EAE. We hypothesized that Na+ channel beta2 subunits (encoded by Scn2b) are involved in MS/EAE pathogenesis, as beta2 is responsible for regulating levels of channel cell surface expression in neurons. We induced non-relapsing EAE in Scn2b(+/+) and Scn2b(-/-) mice on the C57BL/6 background. Scn2b(-/-) mice display a dramatic reduction in EAE symptom severity and lethality as compared to wildtype, with significant decreases in axonal degeneration and axonal loss. Scn2b(-/-) mice show normal peripheral immune cell populations, T cell proliferation, cytokine release, and immune cell infiltration into the CNS in response to EAE, suggesting that Scn2b inactivation does not compromise immune function. Our data suggest that loss of beta2 is neuroprotective in EAE by prevention of Na+ channel up-regulation in response to demyelination.

Repeated exposure to Aspergillus fumigatus conidia results in CD4+ T cell-dependent and -independent pulmonary arterial remodeling in a mixed Th1/Th2/Th17 microenvironment that requires interleukin-4 (IL-4) and IL-10.

ABSTRACT Pulmonary arterial remodeling is a pathological process seen in a number of clinical disease states, driven by inflammatory cells and mediators in the remodeled artery microenvironment. In murine models, Th2 cell-mediated immune responses to inhaled antigens, such as purified Aspergillus allergen, have been reported to induce remodeling of pulmonary arteries. We have previously shown that repeated intranasal exposure of healthy C57BL/6 mice to viable, resting Aspergillus fumigatus conidia leads to the development of chronic pulmonary inflammation and the coevolution of Th1, Th2, and Th17 responses in the lungs. Our objective was to determine whether repeated intranasal exposure to Aspergillus conidia would induce pulmonary arterial remodeling in this mixed Th inflammatory microenvironment. Using weekly intranasal conidial challenges, mice developed robust pulmonary arterial remodeling after eight exposures (but not after two or four). The process was partially mediated by CD4+ T cells and by interleukin-4 (IL-4) production, did not require eosinophils, and was independent of gamma interferon (IFN-γ) and IL-17. Furthermore, remodeling could occur even in the presence of strong Th1 and Th17 responses. Rather than serving an anti-inflammatory function, IL-10 was required for the development of the Th2 response to A. fumigatus conidia. However, in contrast to previous studies of pulmonary arterial remodeling driven by the A. fumigatus allergen, viable conidia also stimulated pulmonary arterial remodeling in the absence of CD4+ T cells. Remodeling was completely abrogated in IL-10−/− mice, suggesting that a second, CD4+ T cell-independent, IL-10-dependent pathway was also driving pulmonary arterial remodeling in response to repeated conidial exposure.

Tryptophan Catabolism Restricts IFN-γ–Expressing Neutrophils and Clostridium difficile Immunopathology

The interplay between Clostridium difficile and the host’s metabolome is believed to influence the severity of infection. However, the mechanism for this phenomenon remains unclear. In this study, we model one of these metabolic pathways by focusing on tryptophan metabolism in the host. We found that inhibition of tryptophan catabolism in IDO1-knockout mice led to increased mucosal destruction, cecal hemorrhage, and increased production of IFN-γ in response to C. difficile infection, but no significant change in mucosal effector or regulatory T cell numbers or IL-10 mRNA expression. The increased immunopathology in infected IDO1-knockout mice was associated with a lower C. difficile burden and an increased percentage of IFN-γ–expressing neutrophils. We further demonstrated the ability of kynurenine to induce apoptosis in bone marrow–derived neutrophils, whereas the presence of tryptophan reversed this effect, providing a possible mechanism for the increased neutrophil accumulation in IDO1−/− mice. We conclude that C. difficile induces tryptophan catabolism in cecal lamina propria cells, which restricts C. difficile–associated immunopathology and the accumulation of IFN-γ–expressing neutrophils. This might represent a self-regulatory mechanism for neutrophils, via the IFN-γ–IDO1 pathway, to restrict their own accumulation during infection. These findings have important clinical implications because IDO inhibitors are used to treat cancer in clinical trials (in patients particularly susceptible to getting C. difficile infection), and treatment with IDO1 inhibitors may exacerbate the severity of C. difficile colitis.

Gastrointestinal manifestations of systemic sclerosis

In patients with systemic sclerosis (SSc), gastrointestinal (GI)-tract involvement is almost universal. Any segment of the GI tract from mouth to anus can be involved, and GI symptoms are a frequent cause of morbidity. In severe cases, GI-tract involvement can progress to the point of malnutrition requiring parenteral nutrition. GI-tract involvement in SSc contributes to disease-related mortality although mostly as a co-morbidity rather than direct cause of death. The review is intended to help address challenges in the assessment and treatment of GI-tract involvement in SSc.

Meta-Analytic Bayesian Model For Differentiating Intestinal Tuberculosis from Crohn's Disease.

Objectives:Distinguishing intestinal tuberculosis (ITB) from Crohns disease (CD) is difficult, although studies have reported clinical, endoscopic, imaging, and laboratory findings that help to differentiate these two diseases. We aimed to produce estimates of the predictive power of these findings and construct a comprehensive model to predict the probability of ITB vs. CD.Methods:A systematic literature search for studies differentiating ITB from CD was conducted in MEDLINE, PUBMED, and EMBASE from inception until September 2015. Fifty-five distinct meta-analyses were performed to estimate the odds ratio of each predictive finding. Estimates with a significant difference between CD and ITB and low to moderate heterogeneity (I2<50%) were incorporated into a Bayesian prediction model incorporating the local pretest probability.Results:Thirty-eight studies comprising 2,117 CD and 1,589 ITB patients were included in the analyses. Findings in the model that significantly favored CD included male gender, hematochezia, perianal disease, intestinal obstruction, and extraintestinal manifestations; endoscopic findings of longitudinal ulcers, cobblestone appearance, luminal stricture, mucosal bridge, and rectal involvement; pathological findings of focally enhanced colitis; and computed tomographic enterography (CTE) findings of asymmetrical wall thickening, intestinal wall stratification, comb sign, and fibrofatty proliferation. Findings that significantly favored ITB included fever, night sweats, lung involvement, and ascites; endoscopic findings of transverse ulcers, patulous ileocecal valve, and cecal involvement; pathological findings of confluent or submucosal granulomas, lymphocyte cuffing, and ulcers lined by histiocytes; a CTE finding of short segmental involvement; and a positive interferon-γ release assay. The model was validated by gender, clinical manifestations, endoscopic, and pathological findings in 49 patients (27 CD, 22 ITB). The sensitivity, specificity, and accuracy for diagnosis of ITB were 90.9%, 92.6%, and 91.8%, respectively.Conclusions:A Bayesian model based on the meta-analytic results is presented to estimate the probability of ITB and CD calibrated to local prevalence. This model can be applied to patients using a publicly available web application.