No abstract

Neonatal meningitis-associated Escherichia coli (NMEC) is among the leading causes of bacterial meningitis and sepsis in newborn infants. Several virulence factors have been identified as common among NMEC, and have been shownto play an important role in the development of bacteremia and/or meningitis.However, there is significant variability in virulence factor expression between NMEC isolates, and relatively little research has been done to assess the impact of variable virulence factor expression on immune cell activation and the outcome of infection. Here, we investigated the role of NMEC strain-dependent P2X receptor (P2XR) signaling on the outcome of infection in neonatal mice. We found that alpha-hemolysin (HlyA)-expressing NMEC (HlyA + ) induced robust P2XRdependent macrophage cell death in vitro, while HlyA − NMEC did not. P2XRdependent cell death was inflammasome independent, suggesting an uncoupling of P2XR and inflammasome activation in the context of NMEC infection. In vivo inhibition of P2XRs was associated with increased mortality in neonatal mice infected with HlyA + NMEC, but had no effect on the survival of neonatal mice infected with HlyA − NMEC. Furthermore, we found that P2XR-dependent protection against HlyA + NMEC in vivo required macrophages, but not neutrophils or NLRP3. Taken together, these data suggest that HlyA + NMEC activates P2XRs which in turn confers macrophage-dependent protection against infection in neonates. In addition, our findings indicate that strain-dependent virulence factor expression should be taken into account when studying the immune response to NMEC.

Brucellosis, caused by intracellular pathogens of the Brucella genus, often results in chronic and/or lifelong infection. While T cells can contribute to control of Brucella, this typically does not result in sterile immunity, and the mechanisms underlying the inability of T cells to clear infection remain unclear. We previously found that B cells promote susceptibility to Brucella in a CD4+ T cell dependent manner. Here we report that B cell MHCII expression enhances susceptibility to infection, and investigated the role of B cell antigen specificity and presentation in this process. We found that B cell receptor specificity facilitates enhanced susceptibility to infection as well as Brucella entry into B cells in vivo. Investigation of the role of individual B cell subsets demonstrated that follicular B cells can inhibit protective CD4+ T cell responses. Evaluation of CD4+ T cell populations revealed that B lymphocytes promote FoxP3 expression preferentially amongst T follicular cell populations following Brucella infection. Additionally, CD40L blockade enhances protection against Brucella in a B cell dependent manner concomitant with a decrease in T follicular regulatory cells (TFR). Interestingly, PD-1 blockade resulted in an increase in TFR populations as well as an increased susceptibility to Brucella infection in a B and CD4+ T cell-dependent manner. Together, these data suggest B and CD4+ T cell interactions within the follicle promote TFR cell populations which in turn could promote susceptibility to Brucella infection. Supported by NIH Grant:1R21AI135160 NIH Grant:1R01AI150797

Neonatal meningitis-associated Escherichia coli (NMEC) are among the leading causes of bacterial meningitis and sepsis in newborn infants. Several virulence factors have been identified as common among NMEC, and have been shown to play an important role in the development of bacteremia and/or meningitis. However, there is significant variability in virulence factor expression between NMEC isolates, and relatively little research has been done to assess the impact of variable virulence factor expression on immune cell activation and the outcome of infection. Here we investigated the role of NMEC strain-dependent P2X receptor (P2XR) signaling on the outcome of infection in neonatal mice. We found that alpha hemolysin (HlyA)-expressing NMEC (HlyA+) induced robust P2XR-dependent macrophage cell death in vitro, while HlyA− NMEC did not. P2XR-dependent cell death was inflammasome independent, suggesting an uncoupling of P2XR and inflammasome activation in the context of NMEC infection. In vivo inhibition of P2XRs was associated with increased mortality in neonatal mice infected with HlyA+ NMEC, but had no effect on the survival of neonatal mice infected with HlyA− NMEC. Furthermore, we found that P2XR-dependent protection against HlyA+ NMEC in vivo required macrophages, but not neutrophils or NLRP3. Taken together, these data suggest that HlyA+ NMEC activate P2XRs which in turn confers macrophage dependent protection against infection in neonates. In addition, our findings indicate that strain-dependent virulence factor expression should be taken into account when studying the immune response to NMEC. Supported by University of Missouri College of Veterinary Medicine Committee on Research.