Summary 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 development, and regulated the susceptibility to autoimmune inflammation.

Summary The cytokine IL17, and signaling via its heterodimeric IL-17RA/IL-17RC receptor, is critical for host defense against extracellular bacterial and fungal pathogens. Polarized lung epithelial cells express IL-17RA and IL-17RC basolaterally. However, their contribution to IL-17-dependent pulmonary defenses in vivo remains to be determined. To address this, we generated mice with conditional deletion of Il17ra or Il17rc in Scgb1a1-expressing club cells, a major component of the murine bronchiolar epithelium. These mice displayed an impaired ability to recruit neutrophils into the airway lumen in response to IL17, a defect in bacterial clearance upon mucosal challenge with the pulmonary pathogen Klebsiella pneumoniae, and substantially reduced epithelial expression of the chemokine Cxcl5. Neutrophil recruitment and bacterial clearance were restored by intranasal administration of recombinant CXCL5. Our data show that IL-17R signaling in the lung epithelium plays a critical role in establishing chemokine gradients that are essential for mucosal immunity against pulmonary bacterial pathogens.

Cryptococcal meningoencephalitis is responsible for upwards of 15% of HIV-related deaths worldwide and is currently the most common cause of non-viral meningitis in the US, affecting both previously healthy and people with immune suppression caused by cancer chemotherapy, transplantation, and biologic therapies. Despite a continued 30–50% attributable mortality, recommended therapeutic strategies have remained largely unchanged since the 1950s. Recent murine models and human studies examining the role of the immune system in both susceptibility to the infection as well as host damage have begun to influence patient care decisions. The Damage Framework Response, originally proposed in 1999, was recently used to discuss dichotomous etiologies of host damage in cryptococcal disease. These include patients suffering microbiological damage with low host immunity (especially those immunosuppressed with HIV) and those having low (live) microbiological burden but high immune-mediated damage (HIV-related immune reconstitution syndrome and non-HIV-related postinfectious inflammatory response syndrome). Cryptococcal disease in previously healthy hosts, albeit rare, has been known for a long time. Immunophenotyping and dendritic cell-T cell signaling studies on cerebral spinal fluid of these rare patients reveal immune capacity for recognition and T-cell activation pathways including increased levels of HLA-DR and CD56. However, despite effective T-cell signals, brain biopsy and autopsy specimens demonstrated an M2 alternative macrophage polarization and poor phagocytosis of fungal cells. These studies expand the paradigm for cryptococcal disease susceptibility to include a prominent role for immune-mediated damage and suggest a need for careful individual consideration of immune activation during therapy of cryptococcal disease in diverse hosts.

Summary Inducible bronchus associated lymphoid tissue (iBALT) is an ectopic lymphoid structure composed of highly organized T-cell and B-cell zones that forms in the lung in response to infectious or inflammatory stimuli. Here, develop a model for fungal-mediated iBALT formation, using infection with Pneumocystis which induces development of pulmonary lymphoid follicles. Pneumocystis-dependent iBALT structure formation and organization required CXCL13 signaling. Cxcl13 expression was regulated by IL-17 family members, as Il17ra−/−, Il17rb−/−, and Il17rc−/− mice failed to develop iBALT. Interestingly, Il17rb−/− mice have intact Th17 responses, but failed to generate an anti-Pneumocystis Th2 response. Given a role for Th2 and Th17 immunity in iBALT formation, we demonstrated that primary pulmonary fibroblasts synergistically upregulated Cxcl13 transcription following dual stimulation with IL-13 and IL-17A in a STAT3/GATA3 dependent manner. Together, these findings uncover a role for Th2/Th17 cells in regulating Cxcl13 expression and provide an experimental model for fungal-driven iBALT formation.

Rationale: Infection with Pneumocystis, an opportunistic fungal pathogen, can result in fulminant pneumonia in the clinical setting of patients with immunosuppression. In murine models, Pneumocystis has previously been shown to induce a CD4 1 T cell-dependent eosinophilic response in the lung capable of providing protection.Objectives: We sought to explore the role of Pneumocystis in generating asthma-like lung pathology, given the natural eosinophilic response to infection.Methods: Pneumocystis infection or antigen treatment was used to induce asthma-like pathology in wild-type mice. The roles of CD4 1 T cells and eosinophils were examined using antibody depletion and knockout mice, respectively. The presence of anti-Pneumocystis antibodies in human serum samples was detected by ELISA and Western blotting.Measurements and Main Results: Pneumocystis infection generates a strong type II response in the lung that requires CD4 1 T cells. Pneumocystis infection was capable of priming a Th2 response similar to that of a commonly studied airway allergen, the house dust mite. Pneumocystis antigen treatment was also capable of inducing allergic inflammation in the lung, resulting in anti-Pneumocystis IgE production, goblet cell hyperplasia, and increased airway resistance. In the human population, patients with severe asthma had increased levels of anti-Pneumocystis IgG and IgE compared with healthy control subjects. Patients with severe asthma with elevated antiPneumocystis IgG levels had worsened symptom scores and lung parameters such as decreased forced expiratory volume and increased residual volume compared with patients with severe asthma who had low anti-Pneumocystis IgG.Conclusions: The present study demonstrates for the first time, to our knowledge, that Pneumocystis is an airway allergen capable of inducing asthma-like lung pathology.

b Anti-CD20 antibody therapy has been a useful medication for managing non-Hodgkin's 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.

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.

IL-22-IL-22R signaling plays a crucial role in regulating host defenses against extracellular pathogens particularly in the intestine, through the induction of antimicrobial peptides and chemotactic genes. However, the role of IL-22- IL-22R is understudied in Spn lung infection, a prevalent pathogen of pneumonia. This paper presents the findings of IL-22 signaling during a murine model of pneumococcal pneumonia and improvement of bacterial burden upon IL-22 administration. IL-22 was rapidly induced in the lung during pneumococcal infection in wild type mice and Il22−/− mice had higher pneumococcal burdens compared to controls. Additionally, mice with hepatic-specific deletion of Il22ra1 also had higher bacterial burdens in lungs compared to littermate controls after intrapulmonary pneumococcal infection, suggesting that IL-22 signaling in the liver is important to control pneumococcal pneumonia. Thus, we hypothesized that enhancement of IL-22 signaling would control pneumococcal burden in lung tissues in an experimental pneumonia model. Administration of recombinant IL-22 systemically to infected wild type mice decreased bacterial burden in lung and liver at 24 hours post infection. Our in vitro studies also showed that mice treated with IL-22 had increased C3 expression in the liver compared to the isotype control group. Furthermore, serum from mice treated with IL-22 had improved opsonic capacity by increasing C3 binding on Spn. Taken together, endogenous IL-22 and hepatic IL-22R signaling play critical roles in controlling pneumococcal lung burden and systemic IL-22 decreases bacterial burden in the lungs and peripheral organs by potentiating C3 opsonization on bacterial surfaces, through the increase of hepatic C3 expression.