Human transferrin and lactoferrin cooperatively support Neisseria meningitidis colonization in the murine nasopharynx.

Neisseria meningitidis is a human-restricted bacteria that is a normal nasopharyngeal resident, yet it can also disseminate, causing invasive meningococcal disease. Meningococci are highly adapted to life in humans, with human-specific virulence factors contributing to bacterial adhesion, nutrient acquisition and immune evasion. While these factors have been explored in isolation, their relative contribution during infection has not been considered due to their absence in small animal models and their expression by different human cell types not readily combined in either in vitro or ex vivo systems. Herein, we show that transgenic expression of the iron-binding glycoproteins human transferrin and lactoferrin can each facilitate N. meningitidis replication in mouse serum but that transferrin was required to support infection-induced sepsis. While these host proteins are insufficient to allow nasopharyngeal colonization alone, mice co-expressing these and human CEACAM1 support robust colonization. In this case, meningococcal colonization elicits an acute elevation in both transferrin and lactoferrin levels within the upper respiratory mucosa, with transferrin levels remaining elevated while lactoferrin returns to basal levels after establishment of infection. Competitive infection of triple transgenic animals with transferrin- and lactoferrin- binding protein mutants selects for bacteria expressing the transferrin receptor, implicating the critical contribution of transferrin-based iron acquisition to support colonization. These transgenic animals have thus allowed us to disentangle the relative contribution of three virulence factors during colonization and invasive disease, and provides a novel in vivo model that can support extended meningococcal colonization, opening a new avenue to explore the meningococcal lifestyle within its primary niche.

Meningococcal vaccine Bexsero elicits a robust cellular immune response that targets but is not consistently protective against Neisseria gonorrhoeae during murine vaginal infection.

Retrospective epidemiological studies suggest that the licensed serogroup B meningococcal vaccine 4CMenB (Bexsero) provides some protection against the closely related pathogen Neisseria gonorrhoeae in humans. This result has been replicated in murine models of gonococcal colonization, with a gonococci-reactive humoral response and more rapid clearance of vaginal infection. However, immunization with Bexsero consistently elicits a robust humoral response but does not protect all individuals, so the correlates of protection remain undefined. Herein, we exploit the fact that Bexsero promotes clearance in only a subset of immunized mice to perform a broad analysis of the adaptive response in animals that are or are not protected. We observe that Bexsero vaccination induces high levels of anti-neisserial antibodies in both serum and the vaginal lumen, and a robust cellular response highlighted by an increase in both conventional naive and memory populations as well as unconventional lymphocyte subsets. Multiplex and flow cytometry results show that Bexsero vaccination generates a robust, multi-faceted cytokine response that spans numerous T cell subsets (TH1, TH2, Treg and TH17 responses) and that non-T non-B lymphocytes play an important role in this response, as indicated by an unbiased principal component analysis. Together, this work provides the first comprehensive analysis of the robust humoral and complex cellular response to Bexsero so as to reveal the effector mechanisms that may contribute to immunity against vaginal gonococcal infection.

Glucose Mediates Niche-Specific Repression of Staphylococcus aureus Toxic Shock Syndrome Toxin-1 through the Activity of CcpA in the Vaginal Environment.

Staphylococcus aureus chronically colonizes up to 30% of the human population on the skin or mucous membranes, including the nasal tract or vaginal canal. While colonization is often benign, this bacterium also has the capability to cause serious infections. Menstrual toxic shock syndrome (mTSS) is a serious toxinosis associated with improper use of tampons, which can induce an environment that is favorable to the production of the superantigen known as toxic shock syndrome toxin-1 (TSST-1). To better understand environmental signaling that influences TSST-1 production, we analyzed expression in the prototype mTSS strain S. aureus MN8. Using transcriptional and protein-based analysis in two niche-related media, we observed that TSST-1 expression was significantly higher in synthetic nasal medium (SNM) than in vaginally defined medium (VDM). One major divergence in medium composition was high glucose concentration in VDM. The glucose-dependent virulence regulator gene ccpA was deleted in MN8, and, compared with wild-type MN8, we observed increased TSST-1 expression in the ΔccpA mutant when grown in VDM, suggesting that TSST-1 is repressed by catabolite control protein A (CcpA) in the vaginal environment. We were able to relieve CcpA-mediated repression by modifying the glucose level in vaginal conditions, confirming that changes in nutritional conditions contribute to the overexpression of TSST-1 that can lead to mTSS. We also compared CcpA-mediated repression to other key regulators of tst, finding that CcpA regulation is dominant compared to other characterized regulatory mechanisms. This study underlines the importance of environmental signaling for S. aureus pathogenesis in the context of mTSS. IMPORTANCE Menstrual toxic shock syndrome (mTSS) is caused by strains of Staphylococcus aureus that overproduce a toxin known as toxic shock syndrome toxin-1 (TSST-1). This work studied how glucose levels in a model vaginal environment could influence the amount of TSST-1 that is produced by S. aureus. We found that high levels of glucose repress TSST-1 production, and this is done by a regulatory protein called catabolite control protein A (CcpA). The research also demonstrated that, compared with other regulatory proteins, the CcpA regulator appears to be the most important for maintaining low levels of TSST-1 in the vaginal environment, and this information helps to understand how changes in the vaginal environmental can lead to mTSS.

GLP-1 receptor signaling increases PCSK1 and ß cell features in human α cells.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that potentiates glucose-stimulated insulin secretion. GLP-1 is classically produced by gut L cells; however, under certain circumstances α cells can express the prohormone convertase required for proglucagon processing to GLP-1, prohormone convertase 1/3 (PC1/3), and can produce GLP-1. However, the mechanisms through which this occurs are poorly defined. Understanding the mechanisms by which α cell PC1/3 expression can be activated may reveal new targets for diabetes treatment. Here, we demonstrate that the GLP-1 receptor (GLP-1R) agonist, liraglutide, increased α cell GLP-1 expression in a ß cell GLP-1R-dependent manner. We demonstrate that this effect of liraglutide was translationally relevant in human islets through application of a new scRNA-seq technology, DART-Seq. We found that the effect of liraglutide to increase α cell PC1/3 mRNA expression occurred in a subcluster of α cells and was associated with increased expression of other ß cell-like genes, which we confirmed by IHC. Finally, we found that the effect of liraglutide to increase bihormonal insulin+ glucagon+ cells was mediated by the ß cell GLP-1R in mice. Together, our data validate a high-sensitivity method for scRNA-seq in human islets and identify a potentially novel GLP-1-mediated pathway regulating human α cell function.