Taylor Eddens

Intestinal Interleukin-17 Receptor Signaling Mediates Reciprocal Control of the Gut Microbiota and Autoimmune Inflammation

Interleukin-17 (IL-17) and IL-17 receptor (IL-17R) signaling are essential for regulating mucosal host defense against many invading pathogens. Commensal bacteria, especially segmented filamentous bacteria (SFB), are a crucial factor that drives T helper 17 (Th17) cell development in the gastrointestinal tract. In this study, we demonstrate that Th17 cells controlled SFB burden. Disruption of IL-17R signaling in the enteric epithelium resulted in SFB dysbiosis due to reduced expression of α-defensins, Pigr, and Nox1. When subjected to experimental autoimmune encephalomyelitis, IL-17R-signaling-deficient mice demonstrated earlier disease onset and worsened severity that was associated with increased intestinal Csf2 expression and elevated systemic GM-CSF cytokine concentrations. Conditional deletion of IL-17R in the enteric epithelium demonstrated that there was a reciprocal relationship between the gut microbiota and enteric IL-17R signaling that controlled dysbiosis, constrained Th17 cell development, and regulated the susceptibility to autoimmune inflammation.

Host defenses against bacterial lower respiratory tract infection

Bacterial pneumonia continues to be a significant cause of morbidity and mortality worldwide. Recent studies have shown that lung epithelia signal through pattern recognition receptors to initiate the innate immune response. Other mediators of innate immunity against bacterial pneumonia include transepithelial dendritic cells, alveolar macrophages, and innate produces of IL-17. CD4+ T cells and B cells play a key role in eliminating and preventing the development of bacterial pneumonias. B cell development and maturation can be modulated by the lung epithelia through BAFF and APRIL, furthering our current understanding of the role of epithelial cells in the immune response.

Pseudomonas aeruginosa sabotages the generation of host proresolving lipid mediators

Significance Pseudomonas aeruginosa pulmonary infections cause prolonged and destructive inflammation for cystic fibrosis patients. Despite vigorous neutrophilic responses, P. aeruginosa persists in a chronic hyperinflammatory environment. We show that the P. aeruginosa virulence factor, cystic fibrosis transmembrane conductance regulator inhibitory factor (Cif), promotes sustained airway inflammation by reducing host pro-resolving lipid mediators. Cif hydrolyzes epithelial-derived 14,15-epoxyeicosatrienoic acid, disrupting transcellular production of the proresolving lipid 15-epi lipoxin A4 (15-epi LXA4) by neutrophils. Clinical data from cystic fibrosis patients revealed that Cif abundance correlated with increased inflammation, decreased 15-epi LXA4, and reduced pulmonary function. Our study and the recent identification of Cif homologs in Acinetobacter and Burkholderia species suggest that bacterial epoxide hydrolases represent a novel virulence strategy shared by multiple respiratory pathogens. Recurrent Pseudomonas aeruginosa infections coupled with robust, damaging neutrophilic inflammation characterize the chronic lung disease cystic fibrosis (CF). The proresolving lipid mediator, 15-epi lipoxin A4 (15-epi LXA4), plays a critical role in limiting neutrophil activation and tissue inflammation, thus promoting the return to tissue homeostasis. Here, we show that a secreted P. aeruginosa epoxide hydrolase, cystic fibrosis transmembrane conductance regulator inhibitory factor (Cif), can disrupt 15-epi LXA4 transcellular biosynthesis and function. In the airway, 15-epi LXA4 production is stimulated by the epithelial-derived eicosanoid 14,15-epoxyeicosatrienoic acid (14,15-EET). Cif sabotages the production of 15-epi LXA4 by rapidly hydrolyzing 14,15-EET into its cognate diol, eliminating a proresolving signal that potently suppresses IL-8–driven neutrophil transepithelial migration in vitro. Retrospective analyses of samples from patients with CF supported the translational relevance of these preclinical findings. Elevated levels of Cif in bronchoalveolar lavage fluid were correlated with lower levels of 15-epi LXA4, increased IL-8 concentrations, and impaired lung function. Together, these findings provide structural, biochemical, and immunological evidence that the bacterial epoxide hydrolase Cif disrupts resolution pathways during bacterial lung infections. The data also suggest that Cif contributes to sustained pulmonary inflammation and associated loss of lung function in patients with CF.

Anti-CD20 Antibody Therapy and Susceptibility to Pneumocystis Pneumonia

ABSTRACT Anti-CD20 antibody therapy has been a useful medication for managing non-Hodgkins lymphoma as well as autoimmune diseases characterized by autoantibody generation. CD20 is expressed during most developmental stages of B lymphocytes; thus, CD20 depletion leads to B-lymphocyte deficiency. As the drug has become more widely used, there has been an increase in the number of case reports of patients developing Pneumocystis pneumonia. The role of anti-CD20 in Pneumocystis jirovecii infection is under debate due to the fact that most patients receiving it are on a regimen of multiple immunosuppressive medications. To address the specific role of CD20 depletion in host immunity against Pneumocystis, we examined a murine anti-CD20 depleting antibody. We demonstrated that anti-CD20 alone is permissive for Pneumocystis infection and that anti-CD20 impairs components of type II immunity, such as production of interleukin-4 (IL-4), IL-5, and IL-13 by whole-lung cells, in response to Pneumocystis murina. We also demonstrated that CD4+ T cells from mice treated with anti-CD20 during Pneumocystis infection are incapable of mounting a protective immune response when transferred into Rag1−/− mice. Thus, CD20+ cells are critical for generating protective CD4+ T-cell immune responses against this organism.

Eosinophils Contribute to Early Clearance of Pneumocystis murina Infection

Pneumocystis pneumonia remains a common opportunistic infection in the diverse immunosuppressed population. One clear risk factor for susceptibility to Pneumocystis is a declining CD4+ T cell count in the setting of HIV/AIDS or primary immunodeficiency. Non–HIV-infected individuals taking immunosuppressive drug regimens targeting T cell activation are also susceptible. Given the crucial role of CD4+ T cells in host defense against Pneumocystis, we used RNA sequencing of whole lung early in infection in wild-type and CD4-depleted animals as an unbiased approach to examine mechanisms of fungal clearance. In wild-type mice, a strong eosinophil signature was observed at day 14 post Pneumocystis challenge, and eosinophils were increased in the bronchoalveolar lavage fluid of wild-type mice. Furthermore, eosinophilopoiesis-deficient Gata1tm6Sho/J mice were more susceptible to Pneumocystis infection when compared with BALB/c controls, and bone marrow–derived eosinophils had in vitro Pneumocystis killing activity. To drive eosinophilia in vivo, Rag1−/− mice were treated with a plasmid expressing IL-5 (pIL5) or an empty plasmid control via hydrodynamic injection. The pIL5-treated mice had increased serum IL-5 and eosinophilia in the lung, as well as reduced Pneumocystis burden, compared with mice treated with control plasmid. In addition, pIL5 treatment could induce eosinophilia and reduce Pneumocystis burden in CD4-depleted C57BL/6 and BALB/c mice, but not eosinophilopoiesis-deficient Gata1tm6Sho/J mice. Taken together, these results demonstrate that an early role of CD4+ T cells is to recruit eosinophils to the lung and that eosinophils are a novel candidate for future therapeutic development in the treatment of Pneumocystis pneumonia in the immunosuppressed population.

Therapeutic Role of Interleukin 22 in Experimental Intra-abdominal Klebsiella pneumoniae Infection in Mice.

ABSTRACT Interleukin 22 (IL-22) is an IL-10-related cytokine produced by T helper 17 (Th17) cells and other immune cells that signals via IL-22 receptor alpha 1 (IL-22Ra1), which is expressed on epithelial tissues, as well as hepatocytes. IL-22 has been shown to have hepatoprotective effects that are mediated by signal transducer and activator of transcription 3 (STAT3) signaling. However, it is unclear whether IL-22 can directly regulate antimicrobial programs in the liver. To test this hypothesis, hepatocyte-specific IL-22Ra1 knockout (Il22Ra1 Hep−/−) and Stat3 knockout (Stat3 Hep−/−) mice were generated and subjected to intra-abdominal infection with Klebsiella pneumoniae, which results in liver injury and necrosis. We found that overexpression of IL-22 or therapeutic administration of recombinant IL-22 (rIL-22), given 2 h postinfection, significantly reduced the bacterial burden in both the liver and spleen. The antimicrobial activity of rIL-22 required hepatic Il22Ra1 and Stat3. Serum from rIL-22-treated mice showed potent bacteriostatic activity against K. pneumoniae, which was dependent on lipocalin 2 (LCN2). However, in vivo, rIL-22-induced antimicrobial activity was only partially reduced in LCN2-deficient mice. We found that rIL-22 also induced serum amyloid A2 (SAA2) and that SAA2 had anti-K. pneumoniae bactericidal activity in vitro. These results demonstrate that IL-22, through IL-22Ra1 and STAT3 singling, can induce intrinsic antimicrobial activity in the liver, which is due in part to LCN2 and SAA2. Therefore, IL-22 may be a useful adjunct in treating hepatic and intra-abdominal infections.

Editorial Commentary: Lung Pathology Associated With Pneumocystis Colonization in Infants

with upregulation of mucus in the airway. Pneumocystis infection in humans was first described in malnourished infants at the end of World War II but many clinicians associate the disease with adults who are immunocompromised. Despite the advances in human immunodeficiency virus (HIV) diagnosis and treatment, PCP remains the most common opportunistic infection in individuals diagnosed with HIV and contin

Murine models of Pneumocystis infection recapitulate human primary immune disorders

Despite the discovery of key pattern recognition receptors and CD4+ T cell subsets in laboratory mice, there is ongoing discussion of the value of murine models to reflect human disease. Pneumocystis is an AIDS-defining illness, in which risk of infection is inversely correlated with peripheral CD4+ T cell counts. Due to medical advances in the control of HIV, the current epidemiology of Pneumocystis infection is predominantly due to primary human immunodeficiencies and immunosuppressive therapies. To this end, we found that every human genetic immunodeficiency associated with Pneumocystis infection that has been tested in mice recapitulated susceptibility. For example, humans with a loss-of-function IL21R mutation are severely immunocompromised. We found that IL-21R, in addition to CD4+ T cell intrinsic STAT3 signaling, were required for generating protective antifungal class-switched antibody responses, as well as effector T cell-mediated protection. Furthermore, CD4+ T cell intrinsic IL-21R/STAT3 signaling was required for CD4+ T cell effector responses, including IL-22 production. Recombinant IL-22 administration to Il21r-/- mice induced the expression of a fungicidal peptide, cathelicidin antimicrobial peptide, which showed in vitro fungicidal activity. In conclusion, SPF laboratory mice faithfully replicate many aspects of human primary immunodeficiency and provide useful tools to understand the generation and nature of effector CD4+ T cell immunity.

Follistatin-like protein 1 modulates IL-17 signaling via IL-17RC regulation in stromal cells

Follistatin‐like protein 1 (FSTL‐1) possesses several newly identified roles in mammalian biology, including interleukin (IL)‐17‐driven inflammation, though the mechanism underlying FSTL‐1 influence on IL‐17‐mediated cytokine production is unknown. Using parallel in vitro bone marrow stromal cell models of FSTL‐1 suppression, we employed unbiased microarray analysis to identify FSTL‐1‐regulated genes and pathways that could influence IL‐17‐dependent production of IL‐6 and granulocyte colony‐stimulating factor. We discovered that FSTL‐1 modulates Il17rc gene expression. Specifically, FSTL‐1 was necessary for Il17rc gene transcription, IL‐17RC surface protein expression and IL‐17‐dependent cytokine production. This work identifies a mechanism by which FSTL‐1 influences IL‐17‐driven inflammatory signaling in vitro and reveals a novel function for FSTL‐1, as a modulator of gene expression. Thus enhanced understanding of the interplay between FSTL‐1 and IL‐17‐mediated inflammation may provide insight into potential therapeutic targets of IL‐17‐mediated diseases and warrants ongoing study of in vivo models and clinical scenarios of FSTL‐1‐influenced diseases.

A protracted course of Pneumocystis pneumonia in the setting of an immunosuppressed child with GMS-negative bronchoalveolar lavage

We report a case of Pneumocystis pneumonia in a 5-year-old male with Trisomy 21 and acute lymphoblastic leukemia. The lack of response to trimethoprim-sulfamethoxazole raised concerns for antimicrobial resistance. Further, diagnosis of Pneumocystis in this patient was complicated by a GMS-negative bronchoalveolar lavage despite molecular evidence of Pneumocystis infection.