Defens-IN! Human α-Defensin 5 Acts as an Unwitting Double Agent to Promote Shigella Infection.

Shigella pathogenesis has confounded researchers for years because of its narrow host selectivity and extraordinary infectious capability. In this issue of Immunity, Xu et al. (2018) identify a cunning mechanism whereby Shigella hijacks human α-defensin 5 to enhance its adhesion and subsequent invasion.

ILC1 populations join the border patrol.

It has been unclear whether an innate lymphoid cell (ILC) counterpart to the T helper 1 cell type exists. New studies, including Fuchs et al. (2013) in this issue of Immunity, identify T-bet(+)IFN-γ(+) ILC1 that accumulate in the inflamed intestine of IBD patients.

The intracellular sensor NOD2 induces microRNA-29 expression in human dendritic cells to limit IL-23 release.

NOD2 is an intracellular sensor that contributes to immune defense and inflammation. Here we investigated whether NOD2 mediates its effects through control of microRNAs (miRNAs). miR-29 expression was upregulated in human dendritic cells (DCs) in response to NOD2 signals, and miR-29 regulated the expression of multiple immune mediators. In particular, miR-29 downregulated interleukin-23 (IL-23) by targeting IL-12p40 directly and IL-23p19 indirectly, likely via reduction of ATF2. DSS-induced colitis was worse in miR-29-deficient mice and was associated with elevated IL-23 and T helper 17 signature cytokines in the intestinal mucosa. Crohn's disease (CD) patient DCs expressing NOD2 polymorphisms failed to induce miR-29 upon pattern recognition receptor stimulation and showed enhanced release of IL-12p40 on exposure to adherent invasive E. coli. Therefore, we suggest that loss of miR-29-mediated immunoregulation in CD DCs might contribute to elevated IL-23 in this disease.

Why do intestinal epithelial cells express MHC class II?

Intestinal epithelial cells (IECs) constitute the border between the vast antigen load present in the intestinal lumen and the mucosal immune compartment. Their ability to express antigen processing and presentation machinery evokes the question whether IECs function as non-conventional antigen-presenting cells. Major histocompatibility complex (MHC) class II expression by non-haematopoietic cells, such as IECs, is tightly regulated by the class II transactivator (CIITA) and is classically induced by IFN-γ. As MHC class II expression by IECs is upregulated under inflammatory conditions, it has been proposed to activate effector CD4+ T (Teff) cells. However, other studies have reported contradictory results and instead suggested a suppressive role of antigen presentation by IECs, through regulatory T (Treg)-cell activation. Recent studies investigating the role of MHC class II + exosomes released by IECs also reported conflicting findings of either immune enhancing or immunosuppressive activities. Moreover, in addition to modulating inflammatory responses, recent findings suggest that MHC class II expression by intestinal stem cells may elicit crosstalk that promotes epithelial renewal. A more complete understanding of the different consequences of IEC MHC class II antigen presentation will guide future efforts to modulate this pathway to selectively invoke protective immunity while maintaining tolerance to beneficial antigens.

Multi-center implementation of automated age-adjusted D-dimer results reduces unnecessary PE imaging.

BACKGROUND: Several previous studies have investigated the clinical utility of age-adjusted D-dimer cutoffs for diagnosing pulmonary embolism (PE). OBJECTIVES: We performed a pre/post implementation study, using data from a mid-Atlantic healthcare system comprising 6 hospitals and 400,000 ED visits to determine whether implementing age adjusted D-dimer cutoffs reduced the number of imaging tests performed. METHODS: Retrospective study of all patients who had a D-dimer performed during ED visits between September 2015 to September 2018. On March 21, 2017, the D-dimer upper limit of normal system-wide was increased for patients over 50 to: Age (years) x 0.01µg/mL. D-dimer results were displayed as normal or high based on automated age adjustment. EHR Chart review was performed 1.5 years prior to implementation of age-adjusted D-dimer cutoffs, as well as 1.5 years after to evaluate mortality and test accuracy characteristics such as false negative rates. Comparisons were made using chi-square testing. RESULTS: 22,302 D-dimers were performed pre-implementation of which 10,837 (48.6%) were positive resulting in 7218 (32.3%) imaging studies. After implementation of age-adjusted d-dimer, 25,082 were performed of which 10,851 (43.2%) were positive resulting in 7017 (28.0%) imaging studies. (pre: 48.6%, post: 43.2%; p < 0.01). A significantly lower proportion of patients had a positive d-dimer (pre: 48.6%, post: 43.2%; p < 0.01) and underwent imaging post-implementation (pre: 32.3%, post: 28.0%; p < 0.05) a relative risk reduction of 13.3. This absolute risk reduction of 4.4% is associated with 1104 less scans in the post-implementation group while still increasing test accuracy from 53.7% to 59.2% (p < 0.05). CONCLUSION: Implementation of an automated age-adjusted D-dimer positive reference value reduced CT and V/Q imaging in this population by 4.4% while increasing test accuracy in a regional, heterogeneous six-hospital system.

Understanding immune-microbiota interactions in the intestine.

The past two decades have seen an explosion in research that aims to understand how the dynamic interplay with the gut microbiota impacts host health and disease, establishing a role for the gut microbiota in a plethora of pathologies. Understanding how health-promoting microbiota are established and how beneficial host-microbiota interactions are maintained is of immense biomedical importance. Despite the enormous progress that has been made, our knowledge of the specific microbiota members that mediate these effects and the mechanisms underlying these interactions is rudimentary. The dearth of information regarding the nature of advantageous host-microbiota interactions, and the factors that cause these relationships to go awry, has hampered our ability to realize the therapeutic potential of the microbiota. Here we discuss key issues that limit current knowledge and describe a path forwards to improving our understanding of the contributions of the microbiota to host health.

Colon Cancer in the Land of NOD: NLRX1 as an Intrinsic Tumor Suppressor.

Although best known for inducing inflammasome formation and pyroptosis in myeloid cells, increasing evidence highlights additional roles for Nod-like receptors (NLR) in nonhematopoietic cells. Two recent studies demonstrate that NLRX1 functions as an intrinsic tumor suppressor in intestinal epithelial cells (IEC), by regulating their responses to proliferative signals following intestinal injury.

Interleukin-23 drives intestinal inflammation through direct activity on T cells.

Mutations in the IL23R gene are linked to inflammatory bowel disease susceptibility. Experimental models have shown that interleukin-23 (IL-23) orchestrates innate and T cell-dependent colitis; however, the cell populations it acts on to induce intestinal immune pathology are unknown. Here, using Il23r(-/-) T cells, we demonstrated that T cell reactivity to IL-23 was critical for development of intestinal pathology, but not for systemic inflammation. Through direct signaling into T cells, IL-23 drove intestinal T cell proliferation, promoted intestinal Th17 cell accumulation, and enhanced the emergence of an IL-17A(+)IFN-gamma(+) population of T cells. Furthermore, IL-23R signaling in intestinal T cells suppressed the differentiation of Foxp3(+) cells and T cell IL-10 production. Although Il23r(-/-) T cells displayed unimpaired Th1 cell differentiation, these cells showed impaired proliferation and failed to accumulate in the intestine. Together, these results highlight the multiple functions of IL-23 signaling in T cells that contribute to its colitogenic activity.

Plasmodium vivax Infection Impairs Regulatory T-Cell Suppressive Function During Acute Malaria.

The balance between pro- and antiinflammatory mechanisms is essential to limit immune-mediated pathology, and CD4+ forkhead box P3 (Foxp3+) regulatory T cells (Treg) play an important role in this process. The expression of inhibitory receptors regulates cytokine production by Plasmodium vivax-specific T cells. Our goal was to assess the induction of programmed death-1 (PD-1) and cytotoxic T-lymphocyte antigen (CTLA-4) on Treg during malaria and to evaluate their function. We found that P. vivax infection triggered an increase in circulating Treg and their expression of CTLA-4 and PD-1. Functional analysis demonstrated that Treg from malaria patients had impaired suppressive ability and PD-1+Treg displayed lower levels of Foxp3 and Helios, but had higher frequencies of T-box transcription factor+ and interferon-gamma+ cells than PD-1-Treg. Thus malaria infection alters the function of circulating Treg by triggering increased expression of PD-1 on Treg that is associated with decreased regulatory function and increased proinflammatory characteristics.

Inflammasomes of the intestinal epithelium.

While the functional importance of inflammasomes in blood-derived cell types is well established, it remains poorly understood how inflammasomes in nonhematopoietic cells contribute to mucosal immunity. Recent studies have revealed functional roles of inflammasomes - particularly NAIP/NLRC4, NLRP6, and noncanonical caspase-4 (caspase-11) - within epithelial cells of the gut in mucosal immune defense, inflammation, and tumorigenesis. Here, we review and discuss these findings in the broader context of tissue compartment-specific mucosal immunity. We propose several models whereby activities of the intestinal epithelial inflammasomes converge on mechanisms to remove compromised epithelial cells, maintain host-microbiota mutualism, and communicate with immune cells of the underlying lamina propria.

Modulation of immune development and function by intestinal microbiota.

The immune system must constantly monitor the gastrointestinal tract for the presence of pathogens while tolerating trillions of commensal microbiota. It is clear that intestinal microbiota actively modulate the immune system to maintain a mutually beneficial relation, but the mechanisms that maintain homeostasis are not fully understood. Recent advances have begun to shed light on the cellular and molecular factors involved, revealing that a range of microbiota derivatives can influence host immune functions by targeting various cell types, including intestinal epithelial cells, mononuclear phagocytes, innate lymphoid cells, and B and T lymphocytes. Here, we review these findings, highlighting open questions and important challenges to overcome in translating this knowledge into new therapies for intestinal and systemic immune disorders.

Interleukin-23 restrains regulatory T cell activity to drive T cell-dependent colitis.

Interleukin-23 (IL-23) is an inflammatory cytokine that plays a key role in the pathogenesis of several autoimmune and inflammatory diseases. It orchestrates innate and T cell-mediated inflammatory pathways and can promote T helper 17 (Th17) cell responses. Utilizing a T cell transfer model, we showed that IL-23-dependent colitis did not require IL-17 secretion by T cells. Furthermore, IL-23-independent intestinal inflammation could develop if immunosuppressive pathways were reduced. The frequency of naive T cell-derived Foxp3+ cells in the colon increased in the absence of IL-23, indicating a role for IL-23 in controlling regulatory T cell induction. Foxp3-deficient T cells induced colitis when transferred into recipients lacking IL-23p19, showing that IL-23 was not essential for intestinal inflammation in the absence of Foxp3. Taken together, our data indicate that overriding immunosuppressive pathways is an important function of IL-23 in the intestine and could influence not only Th17 cell activity but also other types of immune responses.

Intestinal homeostasis and its breakdown in inflammatory bowel disease.

Intestinal homeostasis depends on complex interactions between the microbiota, the intestinal epithelium and the host immune system. Diverse regulatory mechanisms cooperate to maintain intestinal homeostasis, and a breakdown in these pathways may precipitate the chronic inflammatory pathology found in inflammatory bowel disease. It is now evident that immune effector modules that drive intestinal inflammation are conserved across innate and adaptive leukocytes and can be controlled by host regulatory cells. Recent evidence suggests that several factors may tip the balance between homeostasis and intestinal inflammation, presenting future challenges for the development of new therapies for inflammatory bowel disease.

Innate lymphoid cells drive interleukin-23-dependent innate intestinal pathology.

The key role of interleukin (IL)-23 in the pathogenesis of autoimmune and chronic inflammatory disorders is supported by the identification of IL-23 receptor (IL-23R) susceptibility alleles associated with inflammatory bowel disease, psoriasis and ankylosing spondylitis. IL-23-driven inflammation has primarily been linked to the actions of T-helper type 17 (TH17) cells. Somewhat overlooked, IL-23 also has inflammatory effects on innate immune cells and can drive T-cell-independent colitis. However, the downstream cellular and molecular pathways involved in this innate intestinal inflammatory response are poorly characterized. Here we show that bacteria-driven innate colitis is associated with an increased production of IL-17 and interferon-gamma in the colon. Stimulation of colonic leukocytes with IL-23 induced the production of IL-17 and interferon-gamma exclusively by innate lymphoid cells expressing Thy1, stem cell antigen 1 (SCA-1), retinoic-acid-related orphan receptor (ROR)-gammat and IL-23R, and these cells markedly accumulated in the inflamed colon. IL-23-responsive innate intestinal cells are also a feature of T-cell-dependent models of colitis. The transcription factor ROR-gammat, which controls IL-23R expression, has a functional role, because Rag-/-Rorc-/- mice failed to develop innate colitis. Last, depletion of Thy1+ innate lymphoid cells completely abrogated acute and chronic innate colitis. These results identify a previously unrecognized IL-23-responsive innate lymphoid population that mediates intestinal immune pathology and may therefore represent a target in inflammatory bowel disease.

Control of intestinal inflammation by interleukin-10.

Twenty years ago, the observation that mice genetically deficient in IL-10 spontaneously developed severe intestinal inflammation, revealed an essential role for IL-10 in the maintenance of intestinal homeostasis. In the intervening period much has been learned about the cellular and molecular factors that are involved in IL-10-mediated regulatory pathways. Elegant experiments with conditional cell-type specific knockout strains have illustrated that IL-10 acts on both myeloid cells and T cells within the intestine to suppress innate and adaptive inflammatory responses and enhance regulatory circuits. Although several distinct cellular sources of IL-10 have been identified in the gut, CD4(+) T cells are a crucial non-redundant source of IL-10 for the regulation of intestinal inflammation. Induction of IL-10 may represent an important means through which intestinal microbiota establishes mutually beneficial commensalism with mammalian hosts, but can be exploited by certain pathogens to facilitate infection. Recent genetic studies in humans have confirmed the essential role of IL-10 in preventing deleterious inflammation in the gut. A better understanding of the molecular pathways involved in IL-10 induction and function in the intestine may facilitate the development of novel therapies for inflammatory bowel disease (IBD).

Type I IFNs regulate effector and regulatory T cell accumulation and anti-inflammatory cytokine production during T cell-mediated colitis.

We explored the function of endogenous type I IFNs (IFN-1) in the colon using the T cell adoptive transfer model of colitis. Colon mononuclear phagocytes (MPs) constitutively produced IFN-1 in a Toll/IL-1R domain-containing adapter-inducing IFN-ß-dependent manner. Transfer of CD4(+)CD45RB(hi) T cells from wild-type (WT) or IFN-α/ß receptor subunit 1 knockout (IFNAR1(-/-)) mice into RAG(-/-) hosts resulted in similar onset and severity of colitis. In contrast, RAG(-/-) × IFNAR1(-/-) double knockout (DKO) mice developed accelerated severe colitis compared with RAG(-/-) hosts when transferred with WT CD4(+)CD45RB(hi) T cells. IFNAR signaling on host hematopoietic cells was required to delay colitis development. MPs isolated from the colon lamina propria of IFNAR1(-/-) mice produced less IL-10, IL-1R antagonist, and IL-27 compared with WT MPs. Accelerated colitis development in DKO mice was characterized by early T cell proliferation and accumulation of CD11b(+)CD103(-) dendritic cells in the mesenteric lymph nodes, both of which could be reversed by systemic administration of IL-1R antagonist (anakinra). Cotransfer of CD4(+)CD25(+) regulatory T cells (Tregs) from WT or IFNAR1(-/-) mice prevented disease caused by CD4(+)CD45RB(hi) T cells. However, WT CD4(+)CD25(+)Foxp3(GFP+) Tregs cotransferred with CD4(+)CD45RB(hi) T cells into DKO hosts failed to expand or maintain Foxp3 expression and gained effector functions in the colon. To our knowledge, these data are the first to demonstrate an essential role for IFN-1 in the production of anti-inflammatory cytokines by gut MPs and the indirect maintenance of intestinal T cell homeostasis by both limiting effector T cell expansion and promoting Treg stability.

Emergency department variation in utilization and diagnostic yield of advanced radiography in diagnosis of pulmonary embolus.

BACKGROUND: There is growing pressure to measure and reduce unnecessary imaging in the emergency department. OBJECTIVE: We study provider and hospital variation in utilization and diagnostic yield for advanced radiography in diagnosis of pulmonary embolism (PE) and to assess patient- and provider-level factors associated with diagnostic yield. METHODS: Retrospective chart review of all adult patients presenting to four hospitals from January 2006 through December 2009 who had a computed tomography or ventilation/perfusion scan to evaluate for PE. Demographic data on the providers ordering the scans were collected. Diagnostic yield (positive scans/total scans ordered) was calculated at the hospital and provider level. The study was not designed to assess appropriateness of imaging. RESULTS: There was significant variation in utilization and diagnostic yield at the hospital level (chi-squared, p < 0.05). Diagnostic yield ranged from 4.2% to 8.2%; after adjusting for patient- and provider-level factors; the two hospitals with an emergency medicine residency training program had higher diagnostic yields (odds ratio [OR] 2.0, 95% confidence interval [CI] 1.6-2.5 and OR 1.9, 95% CI 1.5-2.4). There was no significant variation in diagnostic yield among the 90 providers after adjusting for patient, hospital, and provider characteristics. Providers with < 10 years of experience had lower odds of diagnosing a PE than more experienced graduates (OR 0.8, 95% CI 0.6-0.9). CONCLUSIONS: Although we found significant variation in utilization of advanced radiography for PE and diagnostic yield at the hospital level, there was no significant variation at the provider level after adjusting for patient-, hospital-, and provider-level factors.

Update: Induction of Inflammatory Bowel Disease in Immunodeficient Mice by Injection of Naïve CD4+ T cells (T Cell Transfer Model of Colitis).

The intestinal inflammation induced by injection of naïve CD4+ T cells into lymphocyte-deficient hosts (more commonly known as the T cell transfer model of colitis) shares many features of idiopathic inflammatory bowel disease (IBD) in humans, such as epithelial cell hyperplasia, crypt abscess formation, and dense lamina propria lymphocyte infiltration. As such, it provides a useful tool for studying mucosal immune regulation as it relates to the pathogenesis and treatment of IBD in humans. In the IBD model described here, colitis is induced in Rag (recombination-activating gene)-deficient mice by reconstitution of these mice with naïve CD4+CD45RBhi T cells through adoptive T cell transfer. Although different recipient hosts of cell transfer can be used, Rag-deficient mice are the best characterized and support studies that are both flexible and reproduceable. As described in the Basic Protocol, in most studies the transferred cells consist of naïve CD4+ T cells (CD45RBhi T cells) derived by fluorescence-activated cell sorting from total CD4+ T cells previously purified using immunomagnetic negative selection beads. In a Support Protocol, methods to characterize colonic disease progression are described, including the monitoring of weight loss and diarrhea and the histological assessment of colon pathology. © 2024 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Induction of IBD in Rag-deficient mice by the transfer of naïve CD4+CD45RBhi T cells Support Protocol: Monitoring development of colitis.

Use of the relationship between absolute lymphocyte count and CD4 count to improve earlier consideration of pneumocystis pneumonia in HIV-positive emergency department patients with pneumonia.

BACKGROUND: The ability to accurately assess the level of immunosuppression in HIV+ patients in the emergency department (ED) is often limited and can affect management of these patients. OBJECTIVE: To evaluate the relationship between the absolute lymphocyte count (ALC) and CD4 count in HIV patients admitted through the ED with pneumonia and how utilization of this relationship may affect early consideration and evaluation of Pneumocystis jiroveci pneumonia (PCP). METHODS: Retrospective multicenter 5-year study of HIV+ patients with an ICD-9 diagnosis of pneumonia. Included patients had an ALC measured on ED presentation and a CD4 count measured in < 24 h. A receiver operator curve (ROC), decision plot analysis, and McNemar test of proportions were used to characterize the relationship between study variables. RESULTS: Six hundred eighty six patients were enrolled, 23.2% (95% confidence interval [CI] 20.2-26.1) were diagnosed with PCP. The geometric mean CD4 count and ALC were 81 and 1089, respectively. The correlation between ALC and CD4 was r = 0.60 (95% CI 0.55-65, p < 0.01). The ROC was 0.78 (0.75-0.82). An ALC < 1700 cells/mm(3) had a sensitivity of 84% (95% CI 80-87) and specificity of 55% (95% CI 48-70) for a CD4 < 200 cells/mm(3). An ALC threshold of 1700 cells/mm(3) would have identified 86% of patients with PCP but falsely identified 2.5 patients without PCP for every one accurately identified. CONCLUSION: The ALC threshold of 1700 cells/mm(3) retains significant discriminatory value and would moderately improve identification of patients with a CD4 < 200 cells/mm(3) but is not likely to be reliable as the sole method of early recognition and evaluation of PCP.