Immune exclusion by naturally-acquired secretory IgA to the pneumococcal pilus-1

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Abstract

Successful infection by mucosal pathogens requires overcoming the mucus barrier. To better understand this key step, we performed a survey of the interactions between human respiratory mucus and the human pathogen S. pneumoniae. Pneumococcal adherence to adult human nasal fluid was seen only by isolates expressing pilus-1. Robust binding was independent of pilus-1 adhesive properties but required Fab-dependent recognition of RrgB, the pilus shaft protein, by naturally-acquired secretory immunoglobulin A (sIgA). Pilus-1 binding by specific sIgA led to bacterial agglutination, but adherence required interaction of agglutinated pneumococci and entrapment in mucus particles. To test the effect of these interactions in vivo, pneumococci were preincubated with human sIgA prior to intranasal challenge in a mouse model of colonization. sIgA-treatment resulted in rapid immune exclusion of pilus-expressing pneumococci. Our findings predict that immune exclusion would select for non-piliated isolates in individuals who acquired RrgB-specific sIgA from prior episodes of colonization with piliated strains. Accordingly, genomic data comparing isolates carried by mothers and their children showed that mothers are less likely to be colonized with pilus-expressing strains. Our study provides a specific example of immune exclusion involving naturally-acquired antibody in the human host, a major factor driving pneumococcal adaptation.

Authors

Ulrike Binsker, John A. Lees, Alexandria J. Hammond, Jeffrey N. Weiser

Human colon mucosal biofilms from healthy or colon cancer hosts are carcinogenic

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Abstract

Mucus-invasive bacterial biofilms are identified on the colon mucosa of approximately 50% of colorectal cancer (CRC) patients and approximately 13% of healthy subjects. Here, we test the hypothesis that human colon biofilms comprise microbial communities that are carcinogenic in CRC mouse models. Homogenates of human biofilm-positive colon mucosa were prepared from tumor patients (tumor and paired normal tissues from surgical resections) or biofilm-positive biopsies from healthy individuals undergoing screening colonoscopy; homogenates of biofilm-negative colon biopsies from healthy individuals undergoing screening colonoscopy served as controls. After 12 weeks, biofilm-positive, but not biofilm-negative, human colon mucosal homogenates induced colon tumor formation in 3 mouse colon tumor models (germ-free ApcMinΔ850/+;Il10–/– or ApcMinΔ850/+ and specific pathogen–free ApcMinΔ716/+ mice). Remarkably, biofilm-positive communities from healthy colonoscopy biopsies induced colon inflammation and tumors similarly to biofilm-positive tumor tissues. By 1 week, biofilm-positive human tumor homogenates, but not healthy biopsies, displayed consistent bacterial mucus invasion and biofilm formation in mouse colons. 16S rRNA gene sequencing and RNA-Seq analyses identified compositional and functional microbiota differences between mice colonized with biofilm-positive and biofilm-negative communities. These results suggest human colon mucosal biofilms, whether from tumor hosts or healthy individuals undergoing screening colonoscopy, are carcinogenic in murine models of CRC.

Authors

Sarah Tomkovich, Christine M. Dejea, Kathryn Winglee, Julia L. Drewes, Liam Chung, Franck Housseau, Jillian L. Pope, Josee Gauthier, Xiaolun Sun, Marcus Mühlbauer, Xiuli Liu, Payam Fathi, Robert A. Anders, Sepideh Besharati, Ernesto Perez-Chanona, Ye Yang, Hua Ding, Xinqun Wu, Shaoguang Wu, James R. White, Raad Z. Gharaibeh, Anthony A. Fodor, Hao Wang, Drew M. Pardoll, Christian Jobin, Cynthia L. Sears

Gene fitness landscape of group A streptococcus during necrotizing myositis

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Abstract

Necrotizing fasciitis and myositis are devastating infections characterized by high mortality. Group A streptococcus (GAS) is a common cause of these infections, but the molecular pathogenesis is poorly understood. We report a genome-wide analysis using serotype M1 and M28 strains that identified GAS genes contributing to necrotizing myositis in nonhuman primates (NHP), a clinically relevant model. Using transposon-directed insertion-site sequencing (TraDIS), we identified 126 and 116 GAS genes required for infection by serotype M1 and M28 organisms, respectively. For both M1 and M28 strains, more than 25% of the GAS genes required for necrotizing myositis encode known or putative transporters. Thirteen GAS transporters contributed to both M1 and M28 strain fitness in NHP myositis, including putative importers for amino acids, carbohydrates, and vitamins and exporters for toxins, quorum-sensing peptides, and uncharacterized molecules. Targeted deletion of genes encoding 5 transporters confirmed that each isogenic mutant strain was significantly (P < 0.05) impaired in causing necrotizing myositis in NHPs. Quantitative reverse-transcriptase PCR (qRT-PCR) analysis showed that these 5 genes are expressed in infected NHP and human skeletal muscle. Certain substrate-binding lipoproteins of these transporters, such as Spy0271 and Spy1728, were previously documented to be surface exposed, suggesting that our findings have translational research implications.

Authors

Luchang Zhu, Randall J. Olsen, Stephen B. Beres, Jesus M. Eraso, Matthew Ojeda Saavedra, Samantha L. Kubiak, Concepcion C. Cantu, Leslie Jenkins, Amelia R. L. Charbonneau, Andrew S. Waller, James M. Musser

Human tryptophanyl-tRNA synthetase is an IFN-γ–inducible entry factor for Enterovirus

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Abstract

Enterovirus 71 (EV-A71) receptors that have been identified to date cannot fully explain the pathogenesis of EV-A71, which is an important global cause of hand-foot-and-mouth disease and life-threatening encephalitis. We identified an interferon-gamma (IFNγ)-inducible EV-A71 cellular entry factor, human tryptophanyl-tRNA synthetase (hWARS), using genome-wide RNAi library screening. The importance of hWARS in mediating virus entry and infectivity was confirmed by virus attachment, in vitro pull-down, antibody/antigen blocking, and CRISPR/Cas9. Upon IFNγ treatment, induced hyperexpression and plasma membrane translocation of hWARS were observed, which sensitized semi-permissive (human neuronal NT2)/non-permissive (mouse fibroblast L929) cells to EV-A71 infection. Our hWARS-transduced mouse infection model showed pathological changes similar to patients with severe EV-A71 infection. The expression of hWARS is also required for productive infection by other human enteroviruses, including the clinically important CV-A16 and EV-D68. This is the first report on the discovery of an entry factor, hWARS, which can be induced by IFNγ for EV-A71. Given that a high level of IFNγ was observed in patients with severe EV-A71 infection, our findings extend the knowledge of the pathogenicity of EV-A71 in relation to the expression of entry factor upon IFNγ stimulation and the therapeutic options for treating severe EV-A71-associated complications.

Authors

Man Lung Yeung, Lilong Jia, Cyril C.Y. Yip, Jasper F.W. Chan, Jade L.L. Teng, Kwok-Hung Chan, Jian-Piao Cai, Chaoyu Zhang, Anna J. Zhang, Wan-Man Wong, Kin-Hang Kok, Susanna K.P. Lau, Patrick C.Y. Woo, Janice Y.C. Lo, Dong-Yan Jin, Shin-Ru Shih, Kwok-Yung Yuen

Pneumococcal meningitis is promoted by single cocci expressing pilus adhesin RrgA

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Abstract

Streptococcus pneumoniae (pneumococcus) is the primary cause of bacterial meningitis. Pneumococcal bacteria penetrates the blood-brain barrier (BBB), but the bacterial factors that enable this process are not known. Here, we determined that expression of pneumococcal pilus-1, which includes the pilus adhesin RrgA, promotes bacterial penetration through the BBB in a mouse model. S. pneumoniae that colonized the respiratory epithelium and grew in the bloodstream were chains of variable lengths; however, the pneumococci that entered the brain were division-competent, spherical, single cocci that expressed adhesive RrgA–containing pili. The cell division protein DivIVA, which is required for an ovoid shape, was localized at the poles and septum of pneumococcal chains of ovoid, nonseparated bacteria, but was absent in spherical, single cocci. In the bloodstream, a small percentage of pneumococci appeared as piliated, RrgA-expressing, DivIVA-negative single cocci, suggesting that only a minority of S. pneumoniae are poised to cross the BBB. Together, our data indicate that small bacterial cell size, which is signified by the absence of DivIVA, and the presence of an adhesive RrgA-containing pilus-1 mediate pneumococcal passage from the bloodstream through the BBB into the brain to cause lethal meningitis.

Authors

Federico Iovino, Disa L. Hammarlöf, Genevieve Garriss, Sarah Brovall, Priyanka Nannapaneni, Birgitta Henriques-Normark

Blood kinetics of Ebola virus in survivors and nonsurvivors

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Abstract

BACKGROUND. Infection with Ebola virus (EBOV) results in a life-threatening disease, with reported mortality rates between 50%–70%. The factors that determine patient survival are poorly understood; however, clinical observations indicate that EBOV viremia may be associated with fatal outcome. We conducted a study of the kinetics of Zaire EBOV viremia in patients with EBOV disease (EVD) who were managed at an Ebola Treatment Centre in Sierra Leone during the recent West African outbreak.

METHODS. Data from 84 EVD patients (38 survivors, 46 nonsurvivors) were analyzed, and EBOV viremia was quantified between 2 and 13 days after symptom onset. Time since symptom onset and clinical outcome were used as independent variables to compare EBOV viral kinetics in survivors and nonsurvivors.

RESULTS. In all patients, EBOV viremia kinetics was a quadratic function of time; however, EBOV viremia was 0.94 logarithm (log) copies per ml (cp/ml) (P = 0.011) higher in survivors than in nonsurvivors from day 2 after the onset of symptoms. Survivors reached peak viremia levels at an earlier time after symptom onset than nonsurvivors (day 5 versus day 7) and had lower mean peak viremia levels compared with nonsurvivors (7.46 log cp/ml; 95% CI, 7.17–7.76 vs. 8.60 log cp/ml; 95% CI, 8.27–8.93). Before reaching peak values, EBOV viremia similarly increased both in survivors and nonsurvivors; however, the decay of viremia after the peak was much stronger in survivors than in nonsurvivors.

CONCLUSION. Our results demonstrate that plasma concentrations of EBOV are markedly different between survivors and nonsurvivors at very early time points after symptom onset and may be predicative of outcome. Further studies focused on the early phase of the disease will be required to identify the causal and prognostic factors that determine patient outcome.

FUNDING. Italian Ministry of Health; Italian Ministry of Foreign Affairs; EMERGENCY’s private donations; and Royal Engineers for DFID–UK.

Authors

Simone Lanini, Gina Portella, Francesco Vairo, Gary P Kobinger, Antonio Pesenti, Martin Langer, Soccoh Kabia, Giorgio Brogiato, Jackson Amone, Concetta Castilletti, Rossella Miccio, Alimuddin Zumla, Maria Rosaria Capobianchi, Antonino Di Caro, Gino Strada, Giuseppe Ippolito, INMI-EMERGENCY EBOV Sierra Leone Study group

STIM1 controls T cell–mediated immune regulation and inflammation in chronic infection

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Abstract

Chronic infections induce a complex immune response that controls pathogen replication, but also causes pathology due to sustained inflammation. Ca²⁺ influx mediates T cell function and immunity to infection, and patients with inherited mutations in the gene encoding the Ca²⁺ channel ORAI1 or its activator stromal interaction molecule 1 (STIM1) are immunodeficient and prone to chronic infection by various pathogens, including Mycobacterium tuberculosis (Mtb). Here, we demonstrate that STIM1 is required for T cell–mediated immune regulation during chronic Mtb infection. Compared with WT animals, mice with T cell–specific Stim1 deletion died prematurely during the chronic phase of infection and had increased bacterial burdens and severe pulmonary inflammation, with increased myeloid and lymphoid cell infiltration. Although STIM1-deficient T cells exhibited markedly reduced IFN-γ production during the early phase of Mtb infection, bacterial growth was not immediately exacerbated. During the chronic phase, however, STIM1-deficient T cells displayed enhanced IFN-γ production in response to elevated levels of IL-12 and IL-18. The lack of STIM1 in T cells was associated with impaired activation-induced cell death upon repeated TCR engagement and pulmonary lymphocytosis and hyperinflammation in Mtb-infected mice. Chronically Mtb-infected, STIM1-deficient mice had reduced levels of inducible regulatory T cells (iTregs) due to a T cell–intrinsic requirement for STIM1 in iTreg differentiation and excessive production of IFN-γ and IL-12, which suppress iTreg differentiation and maintenance. Thus, STIM1 controls multiple aspects of T cell–mediated immune regulation to limit injurious inflammation during chronic infection.

Authors

Ludovic Desvignes, Carl Weidinger, Patrick Shaw, Martin Vaeth, Theo Ribierre, Menghan Liu, Tawania Fergus, Lina Kozhaya, Lauren McVoy, Derya Unutmaz, Joel D. Ernst, Stefan Feske

Biomarkers on patient T cells diagnose active tuberculosis and monitor treatment response

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Abstract

BACKGROUND. The identification and treatment of individuals with tuberculosis (TB) is a global public health priority. Accurate diagnosis of pulmonary active TB (ATB) disease remains challenging and relies on extensive medical evaluation and detection of Mycobacterium tuberculosis (Mtb) in the patient’s sputum. Further, the response to treatment is monitored by sputum culture conversion, which takes several weeks for results. Here, we sought to identify blood-based host biomarkers associated with ATB and hypothesized that immune activation markers on Mtb-specific CD4⁺ T cells would be associated with Mtb load in vivo and could thus provide a gauge of Mtb infection.

METHODS. Using polychromatic flow cytometry, we evaluated the expression of immune activation markers on Mtb-specific CD4⁺ T cells from individuals with asymptomatic latent Mtb infection (LTBI) and ATB as well as from ATB patients undergoing anti-TB treatment.

RESULTS. Frequencies of Mtb-specific IFN-γ⁺CD4⁺ T cells that expressed immune activation markers CD38 and HLA-DR as well as intracellular proliferation marker Ki-67 were substantially higher in subjects with ATB compared with those with LTBI. These markers accurately classified ATB and LTBI status, with cutoff values of 18%, 60%, and 5% for CD38⁺IFN-γ⁺, HLA-DR⁺IFN-γ⁺, and Ki-67⁺IFN-γ⁺, respectively, with 100% specificity and greater than 96% sensitivity. These markers also distinguished individuals with untreated ATB from those who had successfully completed anti-TB treatment and correlated with decreasing mycobacterial loads during treatment.

CONCLUSION. We have identified host blood-based biomarkers on Mtb-specific CD4⁺ T cells that discriminate between ATB and LTBI and provide a set of tools for monitoring treatment response and cure.

TRIAL REGISTRATION. Registration is not required for observational studies.

FUNDING. This study was funded by Emory University, the NIH, and the Yerkes National Primate Center.

Authors

Toidi Adekambi, Chris C. Ibegbu, Stephanie Cagle, Ameeta S. Kalokhe, Yun F. Wang, Yijuan Hu, Cheryl L. Day, Susan M. Ray, Jyothi Rengarajan

Collective nitric oxide production provides tissue-wide immunity during Leishmania infection

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Abstract

Nitric oxide (NO) production is critical for the host defense against intracellular pathogens; however, it is unclear whether NO-dependent control of intracellular organisms depends on cell-intrinsic or cell-extrinsic activity of NO. For example, NO production by infected phagocytes may enable these cells to individually control their pathogen burden. Alternatively, the ability of NO to diffuse across cell membranes might be critical for infection control. Here, using a murine ear infection model, we found that, during infection with the intracellular parasite Leishmania major, expression of inducible NO synthase does not confer a cell-intrinsic ability to lower parasite content. We demonstrated that the diffusion of NO promotes equally effective parasite killing in NO-producing and bystander cells. Importantly, the collective production of NO by numerous phagocytes was necessary to reach an effective antimicrobial activity. We propose that, in contrast to a cell-autonomous mode of pathogen control, this cooperative mechanism generates an antimicrobial milieu that provides the basis for pathogen containment at the tissue level.

Authors

Romain Olekhnovitch, Bernhard Ryffel, Andreas J. Müller, Philippe Bousso

Soluble TNFRp75 regulates host protective immunity against Mycobacterium tuberculosis

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Abstract

Development of host protective immunity against Mycobacterium tuberculosis infection is critically dependent on the inflammatory cytokine TNF. TNF signals through 2 receptors, TNFRp55 and TNFRp75; however, the role of TNFRp75-dependent signaling in immune regulation is poorly defined. Here we found that mice lacking TNFRp75 exhibit greater control of M. tuberculosis infection compared with WT mice. TNFRp75^–/– mice developed effective bactericidal granulomas and demonstrated increased pulmonary recruitment of activated DCs. Moreover, IL-12p40–dependent migration of DCs to lung draining LNs of infected TNFRp75^–/– mice was substantially higher than that observed in WT M. tuberculosis–infected animals and was associated with enhanced frequencies of activated M. tuberculosis–specific IFN-γ–expressing CD4⁺ T cells. In WT mice, TNFRp75 shedding correlated with markedly reduced bioactive TNF levels and IL-12p40 expression. Neutralization of TNFRp75 in M. tuberculosis–infected WT BM-derived DCs (BMDCs) increased production of bioactive TNF and IL-12p40 to a level equivalent to that produced by TNFRp75^–/– BMDCs. Addition of exogenous TNFRp75 to TNFRp75^–/– BMDCs infected with M. tuberculosis decreased IL-12p40 synthesis, demonstrating that TNFRp75 shedding regulates DC activation. These data indicate that TNFRp75 shedding downmodulates protective immune function and reduces host resistance and survival; therefore, targeting TNFRp75 may be beneficial for improving disease outcome.

Authors

Roanne Keeton, Nasiema Allie, Ivy Dambuza, Brian Abel, Nai-Jen Hsu, Boipelo Sebesho, Philippa Randall, Patricia Burger, Elizabeth Fick, Valerie F.J. Quesniaux, Bernhard Ryffel, Muazzam Jacobs