Biology subjects

Seman, B. G.

Publications and source records attributed to Seman, B. G..

3 recordsLinked to original sources

bioRxiv2020

Redundant Trojan horse and endothelial-circulatory mechanisms for host-mediated spread of Candida albicans yeast

The host innate immune system has developed elegant processes for the detection and clearance of invasive fungal pathogens. These strategies may also aid in the spread of pathogens in vivo, although technical limitations have previously hindered our ability to view the host innate immune and endothelial cells to probe their roles in spreading disease. Here, we have leveraged zebrafish larvae as a model to view the interactions of these host processes with the fungal pathogen Candida albicans in vivo. We examined three potential host-mediated mechanisms of fungal spread: movement inside phagocytes in a "Trojan Horse" mechanism, inflammation-assisted spread, and endothelial barrier passage. Utilizing both chemical and genetic tools, we systematically tested the loss of neutrophils and macrophages and the loss of blood flow on yeast cell spread. Both neutrophils and macrophages respond to yeast-locked and wild type C. albicans in our model and time-lapse imaging revealed that macrophages can support yeast spread in a "Trojan Horse" mechanism. Surprisingly, loss of immune cells or inflammation does not alter dissemination dynamics. On the other hand, when blood flow is blocked, yeast can cross into blood vessels but they are limited in how far they travel. Blockade of both phagocytes and circulation reduces rates of dissemination and significantly limits fungal spread distance from the infection site. Together, this data suggests a redundant two-step process whereby (1) yeast cross the endothelium inside phagocytes or via direct uptake, and then (2) they utilize blood flow or phagocytes to travel to distant sites. Author summaryAlthough Candida albicans is the most common cause of fungal bloodstream infection, we know little about how it spreads from one tissue to another. Host processes often inadvertently assist pathogens that can hijack immune cells or induce endothelial endocytosis. Here we have used transparent zebrafish to visualize how specific host cells and processes contribute to yeast spread in vivo. We find that Candida is a sophisticated pathogen that uses redundant strategies to disseminate in the host: it can either use host immune cells or cross into the circulatory system and use blood flow. These data suggest that both of these mechanisms must be targeted to limit Candida dissemination during infection.

microbiology↗

bioRxiv2019

Neonatal granulocytic MDSCs possess phagocytic properties during bacterial infection.

Myeloid-derived suppressor cells (MDSCs) are an immunosuppressive cell type found in high abundance in early life. Currently, there has been limited mechanistic understanding of MDSC phagocytosis of bacteria and the corresponding consequences in the context of acute infection. We set out to determine whether human granulocytic MDSCs have phagocytic capacity that is comparable to other professional phagocytes. To investigate these properties, we utilized fluorescent confocal microscopy, flow cytometry, and bacterial burden assays. We demonstrate that human granulocytic MDSCs phagocytose E. coli O1:K1:H7, and subsequently traffic the bacteria into acidic compartments similar to other phagocytes. However, MDSCs were significantly less efficient at bacterial uptake and killing compared to monocytes. This activity is associated with an inflammatory response, but the amount of TNF gene and protein expression was reduced in infected MDSCs compared to monocytes. Interestingly, we also found that MDSCs release DNA (MeDNA) into the extracellular space that resembles neutrophil extracellular traps. We found that MeDNA had some impact on bacterial viability in single cultures, with an increase in bacterial recovery in MDSCs treated with DNAse. However, MeDNA did not impact the ability of monocytes to eliminate bacteria in co-cultures, suggesting that MDSC extracellular DNA does not compromise monocyte function. Overall, our data reveals mechanistic insight into MDSC activity during infection that includes the kinetics and efficiency of bacterial uptake, elimination through trafficking to acidified compartments, and inflammatory contributions relative to primary human monocytes. These results enhance our understanding of MDSC contributions during acute bacterial infection and identify host-directed targets for immune intervention to improve outcomes and reduce susceptibility to infection early in life.

immunology↗

bioRxiv2019

Elevated levels of interleukin-27 in early life compromise protective immunity during neonatal sepsis

Neonates are at increased risk for bacterial sepsis as a result of immature immunity. We established that the immune suppressive cytokine interleukin (IL)-27 is elevated in early life. In the present work, we hypothesized that increased levels of IL-27 may predispose the neonatal population to more severe infection during sepsis. In a neonatal sepsis model, systemic IL-27 levels continued to rise during infection. Peripheral tissue analysis revealed systemic IL-27 expression, while myeloid cell profiling identified Gr-1 and F4/80-expressing cells as the most abundant producers of IL-27 during infection. Increased IL-27 levels were consistent with increased mortality that was improved in WSX-1-/- mice that lack a functional IL-27 receptor. Infected WSX-1-/- pups exhibited improved weight gain and reduced morbidity. IL-27 signaling in WT mice promoted increased bacterial burdens and systemic inflammation compared to WSX-1-/- neonates. This was consistent with more efficient bacterial killing by Ly6B.2+ myeloid cells and macrophages from WSX-1-deficient compared to wild-type neonates. Live animal imaging further supported a more severe and disseminated infection in WT neonates. This is the first report to describe the impact of elevated early life IL-27 on the host response in neonates while also defining the cell and tissue sources of cytokine. IL-27 is frequently associated with suppressed inflammation. In contrast, our findings demonstrate that IL-27 promotes inflammation during neonatal sepsis by directly compromising control of bacteria that drive the inflammatory response. Collectively, our results suggest that IL-27 represents a therapeutic target to limit susceptibility and improve infectious outcomes in neonatal sepsis.\n\nIMPORTANCEA number of differences in the neonatal immune response compared with adults have been well described. However, a mechanistic understanding of what needs to be overcome in the neonate to generate a more protective immune response during acute bacterial infection has been limited. The work described here helps fill the gap of what is necessary to overcome in order to achieve improved host response to infection. To further the novelty, IL-27 has not previously been attributed to dysfunction or deficiency in neonatal immunity. Our results enhance the understanding of IL-27 biology in the neonatal population while providing evidence that elevated IL-27 levels limit a protective immune response and are detrimental during neonatal sepsis. Strategies aimed at targeting circulating IL-27 concentrations early in life have the potential to improve control of bacterial infection in neonates.

immunology↗