HOST-PATHOGEN INTERACTIONS IN PNEUMOCYSTIS INFECTION

Pneumocystis remains the most common opportunistic infection in patients with HIV/AIDS and can cause a life-threatening fulminant pneumonia. Pneumocystis pneumonia is re-emerging in the HIV-negative population, as immunosuppressive medications have greater use clinically. As the at-risk population increases, understanding the underlying host responses that can lead to protection against Pneumocystis becomes imperative. To that end, we characterized the early CD4+ T-cell dependent eosinophilic response to Pneumocystis murina. Importantly, we demonstrated that eosinophils have potent anti-Pneumocystis activity both in vitro and in vivo. However, eosinophils in the lung can also lead to pathology as seen in allergic airway inflammation in asthma. We therefore compared Pneumocystis to the common airway allergen, house dust mite, and demonstrated that the immune response to both pathogens was highly similar. Pneumocystis antigen exposure resulted in increased airway hyperresponsiveness and mucus production in a Th2-dependent and eosinophil-independent manner. From a translational standpoint, a subset of patients with severe asthma had increased anti-Pneumocystis IgG and IgE antibodies. Patients with high anti-Pneumocystis IgG levels had worsened cough and lung function as measured by spirometry, suggesting that Pneumocystis exposure may be correlated with worsened disease. As Pneumocystis infection induces such a potent adaptive immune response, we next examined local immunity to Pneumocystis. Inducible bronchus associated lymphoid tissue (iBALT) has been characterized in several models of lung infection and contributes to protection. Pneumocystis infection and exposure in a co-housing model resulted in the formation of iBALT structures in a CXCL13-dependent manner. Importantly, CXCL13 regulation appeared to be dependent on both Th2 and Th17 CD4+ T-cells in vivo and in pulmonary fibroblasts in vitro. The host response to Pneumocystis is limited in patients with global immunosuppression and the identification of novel drug and vaccine targets is lacking. Towards that end, we annotated the Pneumocystis genome and as proof-of-principle, demonstrated that the kinome (specifically VPS34) was druggable in vitro. Additionally, we utilized various –omics techniques to identify Meu10 and GSC-1 as novel vaccine targets capable of providing partial protection against Pneumocystis. Together, these studies identified novel protective and pathologic immune responses to Pneumocystis and enabled a top-down approach of anti-Pneumocystis therapeutic development

Pseudomonas Aeruginosa Sabotages the Generation of Host Proresolving Lipid Mediators

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

Effect of Age and Vaccination on Extent and Spread of Chlamydia pneumoniae Infection in C57BL/6 Mice

BACKGROUND: Chlamydia pneumoniae is an obligate intracellular respiratory pathogen for humans. Infection by C. pneumoniae may be linked etiologically to extra-respiratory diseases of aging, especially atherosclerosis. We have previously shown that age promotes C. pneumoniae respiratory infection and extra-respiratory spread in BALB/c mice. FINDINGS: Aged C57BL/6 mice had a greater propensity to develop chronic and/or progressive respiratory infections following experimental intranasal infection by Chlamydia pneumoniae when compared to young counterparts. A heptavalent CTL epitope minigene (CpnCTL7) vaccine conferred equal protection in the lungs of both aged and young mice. This vaccine was partially effective in protecting against C. pneumoniae spread to the cardiovascular system of young mice, but failed to provide cardiovascular protection in aged animals. CONCLUSIONS: Our findings suggest that vaccine strategies that target the generation of a C. pneumoniae-specific CTL response can protect the respiratory system of both young and aged animals, but may not be adequate to prevent dissemination of C. pneumoniae to the cardiovascular system or control replication in those tissues in aged animals

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 development, and regulated the susceptibility to autoimmune inflammation

Toward a humanized mouse model of Pneumocystis pneumonia

Pneumocystis is an important opportunistic fungus that causes pneumonia in children and immunocompromised individuals. Recent genomic data show that divergence of major surface glycoproteins may confer speciation and host range selectivity. On the other hand, immune clearance between mice and humans is well correlated. Thus, we hypothesized that humanize mice may provide information about human immune responses involved in controlling Pneumocystis infection. CD34-engrafted huNOG-EXL mice controlled fungal burdens to a greater extent than nonengrafted mice. Moreover, engrafted mice generated fungal-specific IgM. Fungal control was associated with a transcriptional signature that was enriched for genes associated with nonopsonic recognition of trophs (CD209) and asci (CLEC7A). These same genes were downregulated in CD4-deficient mice as well as twins with bare lymphocyte syndrome with Pneumocystis pneumonia

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

Targeted NGS-Based Analysis of <i>Pneumocystis jirovecii</i> Reveals Novel Genotypes

Pneumocystis jirovecii is an important etiological agent of pneumonia that is underdiagnosed due to the inability to culture the organism. The 2019 PERCH study identified Pneumocystis as the top fungal cause of pneumonia in HIV-negative children using a PCR cutoff of 104 copies of Pneumocystis per mL of sample in nasopharyngeal/oropharyngeal (NP/OP) specimens. Given that Pneumocystis consists of an environmental ascus form and a trophic from (the latter is the form that attaches to the lung epithelium), it is possible that life-form-specific molecular assays may be useful for diagnosis. However, to accomplish this goal, these assays require genotypic information, as the current fungal genomic data are largely from the US and Europe. To genotype Pneumocystis across the globe, we developed an NGS-based genotyping assay focused on genes expressed in asci as well as trophs using PERCH throat swabs from Africa, Bangladesh, and Thailand, as well as North American samples. The NGS panel reliably detected 21 fungal targets in these samples and revealed unique genotypes in genes expressed in trophs, including Meu10, an ascospore assembly gene; two in mitochondrial gene ATP8, and the intergenic region between COX1 and ATP8. This assay can be used for enhanced Pneumocystis epidemiology to study outbreaks but also permits more accurate RT-CPR- or CRISPR-based assays to be performed to improve the non-bronchoscopic diagnosis of this under-reported fungal pathogen

Terminally exhausted CD8+ T cells contribute to age-dependent severity of respiratory virus infection

Abstract Background Lower respiratory infections are a leading cause of severe morbidity and mortality among older adults. Despite ubiquitous exposure to common respiratory pathogens throughout life and near universal seropositivity, antibodies fail to effectively protect the elderly. Therefore, we hypothesized that severe respiratory illness in the elderly is due to deficient CD8+ T cell responses. Results Here, we establish an aged mouse model of human metapneumovirus infection (HMPV) wherein aged C57BL/6 mice exhibit worsened weight loss, clinical disease, lung pathology and delayed viral clearance compared to young adult mice. Aged mice generate fewer lung-infiltrating HMPV epitope-specific CD8+ T cells. Those that do expand demonstrate higher expression of PD-1 and other inhibitory receptors and are functionally impaired. Transplant of aged T cells into young mice and vice versa, as well as adoptive transfer of young versus aged CD8+ T cells into Rag1 −/− recipients, recapitulates the HMPV aged phenotype, suggesting a cell-intrinsic age-associated defect. HMPV-specific aged CD8+ T cells exhibit a terminally exhausted TCF1/7− TOX+ EOMES+ phenotype. We confirmed similar terminal exhaustion of aged CD8+ T cells during influenza viral infection. Conclusions This study identifies terminal CD8+ T cell exhaustion as a mechanism of severe disease from respiratory viral infections in the elderly