Roles of natural killer cells in antiviral immunity

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NK cells can kill virus-infected cells and protect against severe infections.

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Long-lived memory NK cells may develop after vaccination or infection.

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NK cells are potent regulatory of antiviral T and B cell responses.

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The role of NK cells in human infection is complex and context-dependent.

Natural killer (NK) cells are important in immune defense against virus infections. This is predominantly considered a function of rapid, innate NK-cell killing of virus-infected cells. However, NK cells also prime other immune cells through the release of interferon gamma (IFN-γ) and other cytokines. Additionally, NK cells share features with long-lived adaptive immune cells and can impact disease pathogenesis through the inhibition of adaptive immune responses by virus-specific T and B cells. The relative contributions of these diverse and conflicting functions of NK cells in humans are poorly defined and likely context-dependent, thereby complicating the development of therapeutic interventions. Here we focus on the contributions of NK cells to disease in diverse virus infections germane to human health.

Allergen presensitization drives an eosinophil-dependent arrest in lung-specific helminth development

This study investigates the relationship between helminth infection and allergic sensitization by assessing the influence of preexisting allergy on the outcome of helminth infections, rather than the more traditional approach in which the helminth infection precedes the onset of allergy. Here we used a murine model of house dust mite-induced (HDM-induced) allergic inflammation followed by Ascaris infection to demonstrate that allergic sensitization drives an eosinophil-rich pulmonary type 2 immune response (Th2 cells, M2 macrophages, type 2 innate lymphoid cells, IL-33, IL-4, IL-13, and mucus) that directly hinders larval development and reduces markedly the parasite burden in the lungs. This effect is dependent on the presence of eosinophils, as eosinophil-deficient mice were unable to limit parasite development or numbers. In vivo administration of neutralizing antibodies against CD4 prior to HDM sensitization significantly reduced eosinophils in the lungs, resulting in the reversal of the HDM-induced Ascaris larval killing. Our data suggest that HDM allergic sensitization drives a response that mimics a primary Ascaris infection, such that CD4+ Th2-mediated eosinophil-dependent helminth larval killing in the lung tissue occurs. This study provides insight into the mechanisms underlying tissue-specific responses that drive a protective response against the early stages of the helminths prior to their establishing long-lasting infections in the host.

Fibroblast-specific integrin-alpha V differentially regulates type 17 and type 2 driven inflammation and fibrosis

Fibroproliferative diseases affect a significant proportion of the world's population. Despite this, core mechanisms driving organ fibrosis of diverse etiologies remain ill defined. Recent studies suggest that integrin-alpha V serves as a master driver of fibrosis in multiple organs. Although diverse mechanisms contribute to the progression of fibrosis, TGF-β and IL-13 have emerged as central mediators of fibrosis during type 1/type 17, and type 2 polarized inflammatory responses, respectively. To investigate if integrin-alpha V interactions or signaling is critical to the development of type 2 fibrosis, we analyzed fibroblast-specific integrin-alpha V knockout mice in three type 2-driven inflammatory disease models. While we confirmed a role for integrin-alpha V in type 17-associated fibrosis, integrin-alpha V was not critical to the development of type 2-driven fibrosis. Additionally, our studies support a novel mechanism through which fibroblasts, via integrin-alpha V expression, are capable of regulating immune polarization. We show that when integrin-alpha V is deleted on fibroblasts, initiation of type 17 inflammation is inhibited leading to a deregulation of type 2 inflammation. This mechanism is most evident in a model of severe asthma, which is characterized by a mixed type 2/type 17 inflammatory response. Together, these findings suggest dual targeting of integrin-alpha V and type 2 pathways may be needed to ameliorate fibrosis and prevent rebound of opposing pro-fibrotic and inflammatory mechanisms. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Enhanced survival following oral and systemic Salmonella enterica serovar Typhimurium infection in polymeric immunoglobulin receptor knockout mice

Background

Polymeric immunoglobulin receptor (pIgR) transport of secretory immunoglobulin A (SIgA) to mucosal surfaces is thought to promote gut integrity and immunity to Salmonella enterica serovar Typhimurium (S. Typhimurium), an invasive pathogen in mice. To elucidate potential mechanisms, we assessed intestinal barrier function and both oral and systemic S. Typhimurium virulence in pIgR knockout (KO) and wildtype (WT) mice.

Methods

In uninfected animals, we harvested jejunal segments for Ussing chamber analyses of transepithelial resistance (TER); mesenteric lymph nodes (mLN) for bacterial culture; and serum and stool for IgA. Separately, we infected mice either orally or intravenously (IV) with S. Typhimurium to compare colonization, tissue dynamics, and inflammation between KOs and WTs.

Results

Uninfected KOs displayed decreased TER and dramatically increased serum IgA and decreased fecal IgA vs. WT; however, KO mLNs yielded fewer bacterial counts. Remarkably, WTs challenged orally with S. Typhimurium exhibited increased splenomegaly, tissue colonization, and pro-inflammatory cytokines vs. pIgR KOs, which showed increased survival following either oral or IV infection.

Conclusions

Absence of pIgR compromises gut integrity but does not exacerbate bacterial translocation nor S. Typhimurium infection. These findings raise the possibility that immune adaptation to increased gut permeability and elevated serum IgA in the setting of SIgA deficiency provides compensatory protection against invasive gut pathogens.

Luminal microvesicles uniquely influence translocating bacteria after SIV infection

Microbial translocation contributes to persistent inflammation in both treated and untreated HIV infection. Although translocation is due in part to a disintegration of the intestinal epithelial barrier, there is a bias towards the translocation of Proteobacteria. We hypothesized that intestinal epithelial microvesicle cargo differs after HIV infection and contributes to biased translocation. We isolated gastrointestinal luminal microvesicles before and after progressive simian immunodeficiency virus (SIV) infection in rhesus macaques and measured miRNA and antimicrobial peptide content. We demonstrate that these microvesicles display decreased miR-28-5p, -484, -584-3p, and -584-5p, and let-7b-3p, as well as increased beta-defensin 1 after SIV infection. We further observed dose-dependent growth sensitivity of commensal Lactobacillus salivarius upon co-culture with isolated microvesicles. Infection-associated microvesicle differences were not mirrored in non-progressively SIV-infected sooty mangabeys. Our findings describe novel alterations of antimicrobial control after progressive SIV infection that influence the growth of translocating bacterial taxa. These studies may lead to the development of novel therapeutics for treating chronic HIV infection, microbial translocation, and inflammation.

Eosinophil trafficking in allergen-mediated pulmonary inflammation relies on IL-13-driven CCL-11 and CCL-24 production by tissue fibroblasts and myeloid cells

Background

The immunologic mechanisms underlying pulmonary type 2 inflammation, including the dynamics of eosinophil recruitment to the lungs, still need to be elucidated.

Objective

We sought to investigate how IL-13-producing TH2 effector cells trigger eosinophil migration in house dust mite (HDM)-driven allergic pulmonary inflammation.

Methods

Multiparameter and molecular profiling of murine lungs with HDM-induced allergy was investigated in the absence of IL-13 signaling by using IL-13Rα1-deficient mice and separately through adoptive transfer of CD4+ T cells from IL-5-deficient mice into TCRα-/- mice before allergic inflammation.

Results

We demonstrated through single-cell techniques that HDM-driven pulmonary inflammation displays a profile characterized by TH2 effector cell-induced IL-13-dominated eosinophilic inflammation. Using HDM-sensitized IL-13Rα1-/- mice, we found a marked reduction in the influx of eosinophils into the lungs along with a significant downregulation of both CCL-11 and CCL-24. We further found that eosinophil trafficking to the lung relies on production of IL-13-driven CCL-11 and CCL-24 by fibroblasts and Ly6C+ (so-called classical) monocytes. Moreover, this IL-13-mediated eotaxin-dependent eosinophil influx to the lung tissue required IL-5-induced eosinophilia. Finally, we demonstrated that this IL-13-driven eosinophil-dominated pulmonary inflammation was critical for limiting bystander lung transiting Ascaris parasites in a model of allergy and helminth interaction.

Conclusion

Our data suggest that IL-5-dependent allergen-specific TH2 effector cell response and subsequent signaling through the IL-13/IL-13Rα1 axis in fibroblasts and myeloid cells regulate the eotaxin-dependent recruitment of eosinophils to the lungs, with multiple downstream consequences, including bystander control of lung transiting parasitic helminths.

Single cell RNA-sequencing profiling to improve the translation between human IBD and in vivo models

Inflammatory bowel disease (IBD) is an umbrella term for two conditions (Crohn's Disease and Ulcerative Colitis) that is characterized by chronic inflammation of the gastrointestinal tract. The use of pre-clinical animal models has been invaluable for the understanding of potential disease mechanisms. However, despite promising results of numerous therapeutics in mouse colitis models, many of these therapies did not show clinical benefits in patients with IBD. Single cell RNA-sequencing (scRNA-seq) has recently revolutionized our understanding of complex interactions between the immune system, stromal cells, and epithelial cells by mapping novel cell subpopulations and their remodeling during disease. This technology has not been widely applied to pre-clinical models of IBD. ScRNA-seq profiling of murine models may provide an opportunity to increase the translatability into the clinic, and to choose the most appropriate model to test hypotheses and novel therapeutics. In this review, we have summarized some of the key findings at the single cell transcriptomic level in IBD, how specific signatures have been functionally validated in vivo, and highlighted the similarities and differences between scRNA-seq findings in human IBD and experimental mouse models. In each section of this review, we highlight the importance of utilizing this technology to find the most suitable or translational models of IBD based on the cellular therapeutic target.

Abrogation of IL-13Rα2 ameliorates acute inflammatory bowel disease

Anti-TNFα agents are commonly used for treatment of patients with inflammatory bowel disease (IBD), yet up to 40% of patients are non-responders for unknown reasons. IL13RA2 mRNA was more abundant in mucosal biopsy samples of patients with active IBD who are non-responders compared to responders, serving as a potential predictive marker for non-responsiveness. IL-13Rα2 is a high affinity decoy receptor for IL-13, a cytokine with both anti-inflammatory and wound healing functions. In this study, we hypothesized that TNFα and IL-17 produced during the initiation of IBD induces IL-13Rα2 production that neutralizes the endogenous anti-inflammatory activity of IL-13. Using an acute dextran sodium sulfate (DSS) model of mouse colitis, we show that DSS increases the production of both systemic and colonic IL-13Rα2 compared to naive controls. DSS-induced colitis was less severe in Il13ra2−/− mice compared to wild type controls as no shortening in the length of the colon was observed. Histological analysis of the distal colon revealed less goblet cell depletion, inflammatory cell infiltration, and submucosal inflammation in DSS-administered Il13ra2−/− mice compared to DSS-administered wild type mice. However, when Il13ra2−/− mice were infected with the nematode Heligmosomoides polygyrus bakeri, the increased IL-13 activity led to significant morbidity during DSS-colitis. Together, these findings suggest that the absence of IL-13Rα2 enhances endogenous IL-13 bioactivity, which protects mice from acute IBD. Yet, results from the nematode infection model suggest this protective activity must be carefully regulated. Collectively, these results suggest that IL-13Rα2 functions as a key regulator of IBD pathogenesis.

Trusting their gut instinct: innate lymphoid cells utilize cytolytic mechanisms to regulate IgA

Immunoglobulin A (IgA) is important for the maintenance of homeostasis between the host and the intestinal microbiome. Antimicrobial IgA is secreted by IgA+ plasma cells that arise from germinal center (GC) reactions within gut-associated lymphoid tissues (GALT). Dysregulation of IgA production, a common condition with an unknown etiology, can lead to the improper clearance of commensal microbes, allowing for pathogenic strains to flourish and cause disease. Thus, a better understanding of the mechanisms involved in IgA production is critical. Our lab has previously shown that natural killer (NK) cells, a type of innate lymphoid cell (ILC), suppress GC responses and long-lived humoral immunity following systemic viral infection of mice. Here we show that depletion of NK1.1-expressing ILCs (e.g. NK, ILC1, ILC3) in specific-pathogen free mice resulted in enhanced T follicular helper cell and GC B cell numbers within GALT. The numbers of lamina propria IgA+ plasma cells were increased and the expression levels of fecal IgA were elevated for weeks after depletion of NK1.1-expressing ILCs. In addition, NK1.1-depletion was associated with alterations to the intestinal microbiome. In mice with defects in cytolytic granule-mediated killing, including perforin-knockout and beige mice, depletion of NK1.1-expressing ILCs did not enhance GALT GC responses or IgA production. This suggests that a cytolytic mechanism is involved in this regulatory process, although the precise target of this killing remains undefined. Thus, innate lymphoid cells within GALT play an important role in determining the balance between host immunity and microbial commensalism, and may represent new therapeutic targets to enhance efficacy of oral vaccines.

X chromosome gene Ddx3x is involved in B-cell development

Ddx3x, located on the X chromosome, belongs to the DEAD box RNA helicase family. Ddx3x is previously implicated in RNA metabolism, cell cycle control, apoptosis, tumorigeneses and viral infections.

In the process of exploring the role of ddx3x in the female predominance of systemic lupus erythematosus, we found abnormalities in B-cell development within conditional ddx3x-deficient mice.

Breeding of ddx3x-floxed mice with Vav1-Cre mice led to deletion of ddx3x in hematopoietic cells (Vav1ddx3x). Ddx3x expression was reduced 80% in the bone marrow (BM) of Vav1ddx3x mice. Hematopoietic deficiency of ddx3x is associated with a reduced proportion and absolute number of B cells, starting at the small pre-B cell stage, and then subsequently immature B cells and mature B cells in bone marrow, relative to wild-type mice. In spleen, the frequency and number of follicular B cells (FOB) were significantly decreased whereas the numbers of marginal zone, germinal center and plasma-blast B cells were sustained. Mixed Vav1ddx3x and wild-type bone marrow chimera mice demonstrated a B-cell intrinsic effect. Surprisingly, despite fewer B cells in the BM and spleen, serum IgM, IgA and IgG titers were elevated in Vav1ddx3x mice, suggesting ddx3x may affect B-cell function as well.

In conclusion, we showed that ddx3x deficiency affects B-cell development resulting in a loss of B cells in bone marrow and the periphery and an increase in serum immunoglobulin levels.