Greenfield, Kara G

Abstract Description Fungal species, such as Candida albicans, are commonly found as part of the normal microbiota in both the skin and intestine. However, these fungal species, including C. albicans, can also become opportunistic pathogens and have been associated with intestinal and allergic disorders. We hypothesized C. albicans colonization could occur in early life when the neonatal microbiota is permissive to pathogens and lacks colonization resistance compared to later times in life. To investigate this question, we sequenced stool of premature and term infants and frequently found C. albicans colonization, suggesting fungal colonization within the human GI tract. To investigate the impact of long-term C. albicans colonization to the immune system, we established colonization by oral administration of C. albicans to neonatal mice. Colonization of C. albicans was associated with increased diversity of bacterial species in the intestinal microbiota at weaning. Additionally, we observed significant increases of inflammatory cytokines IL-17 and G-CSF in the serum. Future research will expand on the impact of C. albicans colonization on the intestinal microbiota and immune systems. Funding Sources Center for Individualized Medicine Microbiome Program Research Team Science Award, Mayo Clinic NIH, NIDDK R01 DK134366 Topic Categories Mucosal and Regional Immunology (MUC)

Abstract Late-onset neonatal sepsis (LOS), a leading cause of neonatal death, can result from pathogenic bacteria disseminating to the bloodstream from the intestinal microbiota. E. coli is the second most commonly isolated pathogen causing LOS. During sepsis, there are significant immune discrepancies between infants and adults, including elevated IL-6 levels in neonates, demonstrating the need for age-specific research. We have developed a murine model of LOS that uses clinical isolates of gut-resident E. coli, which results in rapid pro-inflammatory cytokine production within 6 hours and neonatal mortality within 2–3 days post-infection. Not all enteric E. coli results in inflammation and mortality, and we have classified isolates as “commensal” or “pathogenic”. TLR4−/− mice infected with pathogenic E. coli have a delayed mortality to sepsis, suggesting innate bacterial recognition is required for acute inflammation. To further determine the source of this delay, we have begun investigating signaling pathways during bacterial infection. We found the immune signaling pathway NFκB/AP1 is consistently activated in murine macrophages by commensal and pathogenic bacterial strains. However, only pathogenic bacteria induce elevated IL-6 production by murine macrophages. Interestingly, this response required live bacteria, suggesting lipopolysaccharide alone from E. coli is not sufficient to recapitulate LOS inflammation. Our future directions will explore alternative signaling pathways that are activated uniquely during pathogenic infection and induce a robust inflammatory response. Through this work, we will determine the consequence of specific pro-inflammatory cytokines in neonatal mice during pathogenic infection. Research supported by R03 DK122187.

Abstract Bacterial bloodstream infections (BSIs) remain a significant contributor to neonatal mortality, despite improved hygienic practices in the NICU. Although the understanding of the neonatal immune system has increased greatly over the past decade, why neonates, but not older infants, are susceptible to severe adverse immunopathology – sepsis – in response to bacteremia remains poorly understood. In the present study, we find that postnatal day 5 (P5) neonatal γδ T cells are highly inflammatory during a mouse model of E. coli BSI and are associated with mortality. Furthermore, γδ T cells in P5 mice rapidly produce pro-inflammatory cytokines, such as IFN-γ, IL-17A, and TNFα, and increase their expression of cytotoxic molecules such as granzyme and perforin. Interestingly, blockade of the γδ TCR in vivo is associated with increased survival and decreased pro-inflammatory cytokine production in P5 pups. Signaling and activation via the γδ TCR was confirmed using Nur77-GFP mice, with P5 γδ T cells significantly upregulating expression of Nur77 during in vivo infection. Intriguingly, E. coli BSI in P15 pups results in markedly different γδ T cells responses compared to neonates, despite similar systemic bacterial burden. During bacterial bloodstream infection, P15 pups do not experience mortality, and unergo minimal activation of γδ T cells and production of IFN-γ, IL-17A, and TNFα. Furthermore, BSI infection in P15 Nur77-GFP mice revealed lack of TCR signaling in P15 γδ T cells at this age. In conclusion, the present study reveals rapid age-dependent changes to γδ T cell responses during early life and suggests neonates may be uniquely susceptible to γδ T cell-mediated immunopathology during bacterial bloodstream infection. T32 AI170478-01

Abstract Peripherally-derived RORγt+ regulatory T cells (Tregs) induced in early life are crucial for maintaining oral tolerance later in life, and the loss of these long-lived cells is associated with increased allergic and inflammatory phenotypes in several animal models. We have identified a predominant pathway of luminal antigen delivery that is associated with Treg development. Around weaning, microbial and dietary proteins are delivered to the colonic lamina propria via goblet cell-associated antigen passages (GAPs) and taken up by antigen presenting cells. GAP formation is inhibited by breastmilk-derived epidermal growth factor (EGF) which is highest in maternal milk at parturition and is diminished by weaning. We have previously shown that disruption of this process – via EGF receptor inhibition (EGFRi) day of life (DOL)4–8 or by conditional deletion of EGFR from goblet cells – results in premature antigen delivery. Consequently, this results in an early initial increase in FoxP3 expression in the colon that is unstable and, ultimately, lost by Tregs primed pre-weaning; this suggests that earlier education of T cells is incompatible with regulatory T cell differentiation in early life. EGFRi-treated FoxP3eGFP-Cre-ERT2ROSAlsl-YFP mice, whose FoxP3+ cells were YFP-labeled at DOL21, had a larger number of YFP+ T cells that lost FoxP3 expression than that of control mice, by DOL28. Further, compared to controls, wild-type mice treated with EGFRi DOL4–8 had increased IFNγ, TNFα, and IL-17a-expressing CD4 T cells when challenged with DSS colitis later in life. This suggests that early antigen delivery-associated FoxP3 instability may contribute to an increased propensity toward an inflammatory phenotype later in life.

Abstract Perturbations of the mucosal immune system and the microbiota can lead to allergic disorders with a lifelong impact. With up to 90% of cases diagnosed by age 6, atopic dermatitis represents a unique allergic disorder during early life. Diagnosis of atopic dermatitis is associated with an increased risk for other allergic disorders throughout life. The opportunistic fungal species Candida albicans is often found as part of a dysbiotic microbiota and its presence is associated with increased risk of atopy. While adult mice are unable to be stably colonized with C. albicans without the use of antibiotics, we have found that mice exposed to C. albicans prior to weaning maintain long term colonization in the gut and on the skin. In mice colonized in early life with C. albicans in the GI tract, FoxP3+ T cells were significantly decreased post-weaning in the mesenteric lymph node as well as in the small intestine and colon lamina propria. Colonization by C. albicans resulted in an increased Th17 response, with increased RORγt+ and c-Maf+ T cells in the colon lamina propria. In a clinical observation study, we found C. albicans colonization in the intestine of prematurely born infants, suggesting colonization of the human GI tract with C. albicans may frequently occur. As the microbiota develops with age, the presence of C. albicans may impact the normal course of increasing complexity and diversity in this ecosystem. The establishment of regulatory T cells in early life is vital to maintaining tolerance to commensal organisms throughout life; this disruption in regulatory T cells potentially links colonization by C. albicans to the development of atopy and allergic responses. Supported by grants from Mayo Clinic Center for Individualized Medicine

Abstract Bloodstream infections, causing late-onset neonatal sepsis (LOS), have an incidence rate of 10% in very low birth weight (<1500 grams) infants. Despite the prevalence in neonates, the current understanding of bloodstream infections and the resulting immune response is predominately based on research in adults, which is often a complication of surgery. In contrast, sepsis in infants is often a result of the dissemination of bacteria from the gut. Additionally, observations have shown differences in the neonatal immune response, such as a decrease in gene expression associated with TLR signaling pathways, compared to adults. One question remaining in the field is the age dependent differences in pathogen detection by innate cells, including dendritic cells and macrophages. Use RAW-Blue reporter cells, and splenocytes cultured from mice at different ages, we have found disparate responses to gut-resident E. coli dependent on pathogen status of the bacteria. Specifically, we have observed differential increases in IL-6, TNFα, and IL-1β, along with NFκB activation that is dependent on live bacteria. Additionally, changes in this response were associated with age, suggesting differences in the innate immune response throughout early life. Future directions include measuring RNA expression of dendritic cells and macrophages between the age groups and exploring how the differences contribute to infection outcomes in a model of sepsis. Supported by grants from NIH (DK122187).

Abstract The intestinal epithelial barrier is vital in preventing translocating bacteria and subsequent systemic infections. This protection is provided by host factors, by the intestinal microbiota, and, during early life, by breast milk. While the beneficial functions of breast milk are numerous to the nursing infant, it has been observed that proteins such as antibodies and growth factors are secreted in higher concentrations early during lactation and decrease as the milk matures. One such growth factor, epidermal growth factor (EGF), regulates the development of colonic goblet cell-associated antigen passages (GAPs). Decrease of EGF through disruption of synchronous breastfeeding or deletion of the epidermal growth factor receptor from goblet cells alters the kinetics of GAP formation, which can serve as a passage for pathogenic bacteria. In a murine model of early GAP formation utilizing an inhibitor of EGF receptor, we observed a variety of gut-resident pathogens were able to utilize GAPs to disseminate systemically and cause disease, including Escherichia coli, Enterococcus faecalis, Enterobacter cloacae, and Pseudomonas aeruginosa. In human studies, we found a strong correlation between concentrations of EGF in the diet and stool of very low birth weight infants. Notably, formula-fed infants contained significantly less EGF in both diet and stool. Future work will assess EGF in donor milk, which we find has highly variable EGF concentration. This work has strong implications for how diet influences risk of developing infections from gut-resident pathogens and how maternal EGF present in breastmilk is synchronized to the newborn infant to provide appropriate protection in early life. Supported by grants from NIH (AI144721, DK122187)

Abstract Neonatal sepsis remains a leading cause of death in preterm and low-birthweight infants and can be separated into two groups: early-onset sepsis (EOS) and late-onset sepsis (LOS). Previous studies have shown that LOS can result from translocation of enteric bacteria across the intestinal epithelium, resulting in bloodstream infection. Through metagenomic sequencing we have observed, unsurprisingly, potential sepsis-causing organisms such as Escherichia coli, Staphylococcus aureus, Enterobacter cloacae, and Group B Streptococcus (GBS) in the stool of neonatal intensive care unit patients. Our previous work has shown E. coli can disseminate from the intestines via goblet cells in a model of LOS, but how other bacterial pathogens disseminate remains unclear. GBS is often associated with EOS following in utero infections and vertical transmission from the mother during pregnancy and delivery. However, the ability of gut-residing GBS to cause sepsis in a murine model of LOS is still unknown. Here we infected five-day-old mice by oral gavage with different strains of GBS, but we did not observe GBS translocating the intestinal epithelium in the pups, unlike E. coli. We next induced EOS in newborn mice by vaginally inoculating pregnant mice to assess GBS dissemination and compare the EOS model to our LOS model. After in utero infection, most pups were intestinally colonized with GBS and, interestingly, only pups with GBS colonies in the lungs had systemic GBS infections. This data suggests neonates are at risk of GBS infection in utero, but not following delivery, even if GBS colonizes the neonatal intestine. This work could elucidate the pathogenesis of EOS as compared to LOS, leading to a deeper understanding of modes of GBS transmission. Supported by NIH: DK122187

Abstract The microbiota present on every mucosal surface of the body is imperative for the development and maintenance of the immune system. Disruption of the microbiota from environmental factors can affect immune components in both the mucosal and the systemic immune compartments. Following birth in mammals including humans and mice, the microbiota rapidly develops and matures into a composition generally seen in adults when infants are weaned. Gut microbiota composition is directly affected by feeding type, breast-fed vs formula-feeding, in humans, and the microbiota associated with breastfeeding has been shown to promote intestinal health. As the composition of breastmilk changes throughout lactation, we hypothesize maternal provided factors within breastmilk support the development of the microbiota in a temporally sensitive manner. To address this question we asynchronously cross-fostered (ACF) litters born on day 1 to dams who had delivered 2 weeks earlier. Gut microbiota composition was assessed by 16S analysis of stool samples at the time of weaning, and while the microbiota of synchronous cross-fostered pups resembled the microbiota of their foster dam, the microbiota of ASF mice was different from both their foster dam and the healthy microbiota seen in weanling mice. ACF mice had a significant reduction in bacteroides and firmicute species, species that generally represent the majority of the bacteria within a healthy microbiota, and expansion in prevotella species, which include clinically important opportunistic pathogens, suggesting ACF mice contain a dysbiotic microbiota. Future work will explore and identify what temporally dependent components in breast milk support the development of a healthy microbiota.