ICOS expression is required for maintenance but not the formation of germinal centers in the spleen in response to P. yoelii infection.

Inducible T cell co-stimulator (ICOS) plays a key role in the differentiation and maintenance of follicular helper T (Tfh) cells and thus germinal center (GC) formation. Previously, our lab showed in a Plasmodium chabaudi infection model that Icos -/- mice were significantly impaired in their ability to form GCs despite a persistent infection and thus a continued antigen (Ag) load. Here, we show that resolution of a primary infection with P. yoelii , was delayed in Icos -/- mice. This phenotype was associated with a reduction in the accumulation of Tfh-like and GC Tfh cells and an early deficiency in Ag-specific antibody (Ab) production. However, Icos -/- mice could form GCs, though they were less frequent in number than in wild-type (WT) mice. Nonetheless, the Ag-specific Abs from Icos -/- mice lacked signs of affinity maturation, suggesting functional defects associated with these GCs. Eventually, these GC structures dissipated more rapidly in Icos -/- mice than in WT mice. Moreover, the ability of Icos -/- mice to form these GC structures is not reliant on the high Ag load associated with P. yoelii infections, as GC formation was preserved in Icos -/- mice treated with atovaquone. Finally, mice were unable to form secondary GCs in the absence of ICOS after re-challenge. Overall, these data demonstrate the necessity of ICOS in the maintenance of Tfh cells, the formation and maintenance of sufficient numbers of functioning GCs, and the ability to generate new GC structures after re-infection with P. yoelii .

Evidence for cGAS-STING signaling in the female genital tract resistance to Chlamydia trachomatis infection

Sexually transmitted Chlamydia trachomatis can ascend to the upper genital tract due to its resistance to innate immunity in the lower genital tract. C. trachomatis can activate cGAS-STING signaling pathway in cultured cells via either cGAS or STING. The current study was designed to evaluate the role of the cGAS-STING pathway in innate immunity against C. trachomatis in the mouse genital tract. Following intravaginal inoculation, C. trachomatis significantly declined by day 5 following a peak infection on day 3 while the mouse-adapted C. muridarum continued to rise for >1 week, indicating that C. trachomatis is susceptible to the innate immunity in the female mouse genital tract. This conclusion was supported by the observation of a similar shedding course in mice deficient in adaptive immunity. Thus, C. trachomatis can be used to evaluate innate immunity in the female genital tract. It was found that mice deficient in either cGAS or STING significantly increased the yields of live C. trachomatis on day 5, indicating an essential role of the cGAS-STING signaling pathway in innate immunity of the mouse genital tract. Comparison of live C. trachomatis recovered from different genital tissues revealed that the cGAS-STING-dependent immunity against C. trachomatis was restricted to the mouse lower genital tract regardless of whether C. trachomatis was inoculated intravaginally or transcervically. Thus, we have demonstrated an essential role of the cGAS-STING signaling pathway in innate immunity against chlamydial infection, laying a foundation for further illuminating the mechanisms of the innate immunity in the female lower genital tract.

Stabilization but no functional influence of HIF-1α expression in the intestinal epithelium during Salmonella Typhimurium infection

The hypoxia-inducible transcription factor 1 (HIF-1) has been shown to enhance microbial killing and to ameliorate the course of bacterial infections. While the impact of HIF-1 on inflammatory diseases of the gut has been studied intensively, its function in bacterial infections of the gastrointestinal tract remains largely elusive. With the help of a publicly available gene expression data set, we could infer significant activation of HIF-1 after oral infection of mice with Salmonella Typhimurium. Immunohistochemistry and western blot analysis confirmed marked HIF-1α protein stabilization, especially in the intestinal epithelium. This prompted us to analyze conditional Hif1a -deficient mice to examine cell type-specific functions of HIF-1 in this model. Our results demonstrate enhanced non-canonical induction of HIF-1 activity upon Salmonella infection in the intestinal epithelium as well as in macrophages. Surprisingly, Hif1a deletion in intestinal epithelial cells did not impact on inflammatory gene expression, bacterial spread or disease outcome. In contrast, Hif1a deletion in myeloid cells enhanced intestinal Cxcl2 expression and reduced the cecal Salmonella load. In vitro , HIF-1α-deficient macrophages showed an overall impaired transcription of mRNA encoding pro-inflammatory factors, however, intracellular survival of Salmonella was not impacted by HIF-1α deficiency.

A novel pneumococcal surface protein K of nonencapsulated Streptococcus pneumoniae promotes transmission among littermates in an infant mouse model with influenza A virus co-infection

We established an infant mouse model for colonization and transmission by nonencapsulated Streptococcus pneumoniae (NESp) strains to gain important information about its virulence among children. Invasive pneumococcal diseases have decreased dramatically since the worldwide introduction of pneumococcal capsular polysaccharide vaccines. Increasing prevalence of non-vaccine serotypes including NESp has been highlighted as a challenge in treatment strategy, but the virulence of NESp is not well understood. Protective strategy against NESp colonization and transmission between children require particularly urgent evaluation. NESp lacks capsules, a major virulent factor of pneumococci, but can cause a variety of infections in children and older people. PspK, a specific surface protein of NESp, is a key factor in establishing nasal colonization. In our infant mouse model for colonization and transmission by NESp strains, NESp could establish stable nasal colonization at the same level as encapsulated serotype 6A in infant mice, and could be transmitted between littermates. Transmission was promoted by NESp surface virulence factor PspK and influenza virus co-infection. However, PspK-deletion mutants lost the ability to colonize and transmit to new hosts. Promotion of NESp transmission by influenza was due to increased susceptibility of the new hosts. PspK was a key factor not only in establishment of nasal colonization, but also in transmission to new hosts. PspK may be targeted as a new candidate vaccine for NESp infection in children.

uvrY deletion and acetate reduce gut colonization of Crohn’s disease-associated adherent-invasive Escherichia coli by decreasing expression of type 1 fimbriae

Adherent-invasive Escherichia coli (AIEC) is involved in onset and/or exacerbation of Crohn’s disease. AIEC adapts to the gut environment by altering gene-expression programs, leading to successful gut-lumen colonization. However, the underlying mechanism of gut colonization is still far from clarified. Here, we show the role of UvrY, a response regulator of bacterial two-component signal transduction systems, in AIEC gut colonization. An AIEC mutant lacking the uvrY gene exhibited impairment of competitive colonization in the murine intestinal tract. UvrY contributes to functional expression of type 1 fimbriae by activating expression of small RNA CsrB, which confers adherence and invasion into epithelial cells on AIEC. In contrast, acetate suppresses the UvrY-dependent expression of type 1 fimbriae, resulting in less efficient cell invasion and attenuated gut colonization. Our findings might lead to therapeutic interventions for CD, in which inhibitions of UvrY activation and acetate supplementation reduce the colonization levels of AIEC by decreasing type-1 fimbriae expression.

Dual transcriptomics to determine interferon-gamma independent host response to intestinal Cryptosporidium parvum infection

Animals with a chronic infection of the parasite Toxoplasma gondii are protected against lethal secondary infection with other pathogens. Our group previously determined that soluble T. gondii antigens (STAg) can mimic this protection and be used as a treatment against several lethal pathogens. Because treatments are limited for the parasite Cryptosporidium parvum , we tested STAg as a C. parvum therapeutic. We determined that STAg treatment reduced C. parvum Iowa II oocyst shedding in IFNγ-KO mice. Murine intestinal sections were then sequenced to define the IFNγ independent transcriptomic response to C. parvum infection. Gene Ontology and transcript abundance comparisons showed host immune response and metabolism changes. Transcripts for type I interferon responsive genes were more abundant in C. parvum infected mice treated with STAg. Comparisons between PBS or STAg treatments showed no significant differences in C. parvum gene expression. C. parvum transcript abundance was highest in the ileum and mucin-like glycoproteins and the GDP-fucose transporter were among the most abundant. These results will assist the field in determining both host- and parasite-directed future therapeutic targets.

Distinct serotypes of streptococcal M proteins mediate fibrinogen-dependent platelet activation and pro-inflammatory effects

Sepsis is a life-threatening complication of infection that is characterised by a dysregulated inflammatory state and disturbed hemostasis. Platelets are the main regulators of hemostasis, and they also respond to inflammation. The human pathogen Streptococcus pyogenes can cause local infection that may progress to sepsis. There are more than 200 different serotypes of S. pyogenes defined according to sequence variations in the M protein. The M1 serotype is among ten serotypes that are predominant in invasive infection. M1 protein can be released from the surface and has previously been shown to generate platelet, neutrophil and monocyte activation. The platelet dependent pro-inflammatory effects of other serotypes of M protein associated with invasive infection (M3, M5, M28, M49 and M89) is now investigated using a combination of multiparameter flow cytometry, ELISA, aggregometry and quantitative mass spectrometry. We demonstrate that only M1-, M3- and M5 protein serotypes can bind fibrinogen in plasma and mediate fibrinogen and IgG dependent platelet activation and aggregation, release of granule proteins, upregulation of CD62P to the platelet surface, and complex formation with neutrophils and monocytes. Neutrophil and monocyte activation, determined as upregulation of surface CD11b, is also mediated by M1-, M3- and M5 protein serotypes, while M28-, M49- or M89 proteins failed to mediate activation of platelets or leukocytes. Collectively, our findings reveal novel aspects of the immunomodulatory role of fibrinogen acquisition and platelet activation during streptococcal infections.

Host defense mechanisms induce genome instability leading to rapid evolution in an opportunistic fungal pathogen

The ability to generate genetic variation facilitates rapid adaptation in stressful environments. The opportunistic fungal pathogen Candida albicans frequently undergoes large-scale genomic changes, including aneuploidy and loss-of heterozygosity (LOH), following exposure to host environments. However, the specific host factors inducing C. albicans genome instability remain largely unknown. Here, we leveraged the genetic tractability of nematode hosts to investigate whether innate immune components, including antimicrobial peptides (AMPs) and reactive oxygen species (ROS), induced host-associated C. albicans genome instability. C. albicans associated with immunocompetent hosts carried multiple large-scale genomic changes including LOH, whole chromosome, and segmental aneuploidies. In contrast, C. albicans associated with immunocompromised hosts deficient in AMPs or ROS production had reduced LOH frequencies and fewer, if any, additional genomic changes. To evaluate if extensive host-induced genomic changes had long-term consequences for C. albicans adaptation, we experimentally evolved C. albicans in either immunocompetent or immunocompromised hosts and selected for increased virulence. C. albicans evolved in immunocompetent hosts rapidly increased virulence, but not in immunocompromised hosts. Taken together, this work suggests that host-produced ROS and AMPs induces genotypic plasticity in C. albicans which facilitates rapid evolution.

Transcriptional Profiling of Early and Late Phases of Bovine Tuberculosis.

Bovine tuberculosis, caused by Mycobacterium tuberculosis var. bovis ( M. bovis ), is an important enzootic disease affecting mainly cattle, worldwide. Despite the implementation of national campaigns to eliminate the disease, bovine tuberculosis remains recalcitrant to eradication in several countries. Characterizing the host response to M. bovis infection is crucial for understanding the immunopathogenesis of the disease and for developing better control strategies. To profile the host responses to M. bovis infection, we analyzed the transcriptome of whole blood cells collected from experimentally infected calves with a virulent strain of M. bovis using RNA transcriptome sequencing (RNAseq). Comparative analysis of calf transcriptomes at early (8 weeks) vs. late (20 weeks) aerosol infection with M. bovis revealed divergent and unique profile for each stage of infection. Notably, at the early time point, transcriptional upregulation was observed among several of the top-ranking canonical pathways involved in T-cell chemotaxis. At the late time point, enrichment in the cell mediated cytotoxicity (e.g. Granzyme B) was the predominant host response. These results showed significant change in bovine transcriptional profiles and identified networks of chemokine receptors and monocyte chemoattractant protein (CCL) co-regulated genes that underline the host-mycobacterial interactions during progression of bovine tuberculosis in cattle. Further analysis of the transcriptomic profiles identified potential biomarker targets for early and late phases of tuberculosis in cattle. Overall, the identified profiles better characterized identified novel immunomodulatory mechanisms and provided a list of targets for further development of potential diagnostics for tuberculosis in cattle.

IL-10 deficiency protects hamsters from Leptospira infection

Leptospirosis is a globally spread zoonotic disease with outcomes ranging from subclinical infection to fatal Weil syndrome. In addition to antibiotics, some immune activators have shown protective effects against leptospirosis. However, the unclear relationship between Leptospira and cytokines, has limited the development of antileptospiral immunomodulators. In this study, the particular role of IL-10 in leptospirosis was explored by using IL-10 defective (IL-10 -/- ) hamsters. After Leptospira infection, an improved survival rate, reduced leptospiral burden and alleviation of organ lesions were found in IL-10 -/- hamsters compared with WT hamsters. In addition, the gene expression levels of IL-1β, IL-6 and TNF-α and the NO level were higher in IL-10 -/- hamsters than in WT hamsters. Our results indicate that IL-10 deficiency protects hamsters from Leptospira infection.