Lysates of Methylococcus capsulatus Bath induce a lean-like microbiota, intestinal FoxP3+RORγt+IL-17+ Tregs and improve metabolism

Interactions between host and gut microbial communities are modulated by diets and play pivotal roles in immunological homeostasis and health. We show that exchanging the protein source in a high fat, high sugar, westernized diet from casein to whole-cell lysates of the non-commensal bacterium Methylococcus capsulatus Bath is sufficient to reverse western diet-induced changes in the gut microbiota to a state resembling that of lean, low fat diet-fed mice, both under mild thermal stress (T22 °C) and at thermoneutrality (T30 °C). Concomitant with microbiota changes, mice fed the Methylococcus-based western diet exhibit improved glucose regulation, reduced body and liver fat, and diminished hepatic immune infiltration. Intake of the Methylococcu-based diet markedly boosts Parabacteroides abundances in a manner depending on adaptive immunity, and upregulates triple positive (Foxp3+RORγt+IL-17+) regulatory T cells in the small and large intestine. Collectively, these data point to the potential for leveraging the use of McB lysates to improve immunometabolic homeostasis.publishedVersio

Characterization of group 3 innate lymphoid cell function in the innate and adaptive immune system

Group 3 innate lymphoid cells (ILC3s) play decisive roles in mammalian physiology including lymphoid tissue development, tissue repair and immune regulation. So far, the functions of ILC3s in the adult immune system have been mainly linked to their capacity to release cytokines in response to microbial or inflammatory signals. It could be demonstrated that ILC3s are indispensable for protective immunity against the mouse intestinal pathogen Citrobacter rodentium by the early production of IL-22 in response to IL-23 secreted mainly by dendritic cells (DCs) upon microbial exposure. However, whether ILC3s are able to directly sense and respond to the presence of pathogens thereby contributing to innate immunity is not yet known. Furthermore, whether these cells are capable to interact with cells of the adaptive immune system to meaningfully regulate adaptive immune responses has to be explored. In the present study, I could show that ILC3s directly responded to microbial products such as the Toll-like receptor (TLR) ligands CpG and Poly I:C in vitro. They up-regulated the surface expression of the early activation marker CD69 and secreted IL-22, a cytokine known for its protective immune function in the mucosa. Additionally, I could demonstrate that in vivo challenge with TLR ligands CpG and LPS was able to induce ILC3 activation in vivo. Furthermore, ILC3s produced high amounts of IL-17 and IL-22 upon exposure to the pro-inflammatory cytokine IL-1β. IL-1β emerged as a strong activator of ILC3s as its presence induced the production of a broad range of cytokines by ILC3s. Altogether, the response of ILC3s varied depending on the nature of innate stimuli. In addition, I could demonstrate that upon IL-1β exposure, peripheral ILC3s up-regulated the expression of surface major histocompatibility complex class II (MHC II) molecules and expressed co-stimulatory molecules reminiscent of an antigen-presenting cell-like phenotype. Further, I found that ILC3s could take up latex beads, process protein antigen (Ag) and consequently prime CD4+ T cell responses in vitro. The cognate interaction of ILC3s and CD4+ T cells led to T cell proliferation both in vitro and in vivo. By using a mouse model with MHC II deficiency exclusively in ILC3s I could demonstrate that the disruption of Ag-dependent interaction of ILC3s and CD4+ T cells impaired specific T cell and T-dependent B cell responses in vivo. In addition, I found that IL-1β-activated peripheral ILC3s were more efficient than non-activated ILC3s in the induction of CD4+ T cell responses. ILC3-CD4+ T cell interactions turned out to be bidirectional and led to the activation of ILC3s. The activating feedback loop of CD4+ T cells to ILC3s was most likely mediated by soluble factors produced by CD4+ T cells upon Ag encounter. Taken together, my data reveal an activation-dependent function of peripheral ILC3s in eliciting cognate CD4+ T cell immune responses, ascribing to them a novel function in adaptive immunity. Finally, I found that small intestinal ILC3s and peripheral ILC3s differed from each other in regard to their phenotype, responsiveness to IL-1β and immune function. In contrast to peripheral ILC3s, small intestinal ILC3s expressed high levels of CD69 on their surface suggesting an activated phenotype. I could show that CD69 expression was independent of TLR- and IL-1R signaling, the presence of T and B cells, or the microbiota as well as the availability of IL-23. In addition, small intestinal ILC3s were not able to increase the expression of MHC II molecules and to express co-stimulatory molecules upon IL-1β exposure. Although they were able to take up latex beads and to process exogenous Ag, they were far less efficient in CD4+ T cell activation than peripheral ILC3s. However, they were capable to produce high amounts of IL-22 in response to IL-1β stimulation. Taken together, these data suggest that the immune functions of ILC3s are tissue specific and might be regulated by environmental factors and/or interactions with tissue-specific cells

Flt3 Ligand Regulates the Development of Innate Lymphoid Cells in Fetal and Adult Mice

Flt3 ligand (Flt3L) promotes survival of lymphoid progenitors in the bone marrow and differentiation of dendritic cells (DCs), but its role in regulating innate lymphoid cells (ILCs) during fetal and adult life is not understood. By using Flt3L knockout and transgenic mice, we demonstrate that Flt3L controls ILC numbers by regulating the pool of α4β7(-) and α4β7(+) lymphoid tissue inducer cell progenitors in the fetal liver and common lymphoid progenitors in the bone marrow. Deletion of flt3l severely reduced the number of fetal liver progenitors and lymphoid tissue inducer cells in the neonatal intestine, resulting in impaired development of Peyer's patches. In the adult intestine, NK cells and group 2 and 3 ILCs were severely reduced. This effect occurred independently of DCs as ILC numbers were normal in mice in which DCs were constitutively deleted. Finally, we could show that administration of Flt3L increased the number of NKp46(-) group 3 ILCs in wild-type and even in Il7(-/-) mice, which generally have reduced numbers of ILCs. Taken together, Flt3L significantly contributes to ILC and Peyer's patches development by targeting lymphoid progenitor cells during fetal and adult life

Microbiota-induced tissue signals regulate ILC3-mediated antigen presentation

Abstract Although group 3 innate lymphoid cells (ILC3s) are efficient inducers of T cell responses in the spleen, they fail to induce CD4+ T cell proliferation in the gut. The signals regulating ILC3-T cell responses remain unknown. Here, we show that transcripts associated with MHC II antigen presentation are down-modulated in intestinal natural cytotoxicity receptor (NCR)- ILC3s. Further data implicate microbiota-induced IL-23 as a crucial signal for reversible silencing of MHC II in ILC3s, thereby reducing the capacity of ILC3s to present antigen to T cells in the intestinal mucosa. Moreover, IL-23-mediated MHC II suppression is dependent on mTORC1 and STAT3 phosphorylation in NCR- ILC3s. By contrast, splenic interferon-γ induces MHC II expression and CD4+ T cell stimulation by NCR- ILC3s. Our results thus identify biological circuits for tissue-specific regulation of ILC3-dependent T cell responses. These pathways may have implications for inducing or silencing T cell responses in human diseases. Conflict of interest statemen

Bifidobacterium species associated with breastfeeding produce aromatic lactic acids in the infant gut

Breastfeeding profoundly shapes the infant gut microbiota, which is critical for early life immune development, and the gut microbiota can impact host physiology in various ways, such as through the production of metabolites. However, few breastmilk-dependent microbial metabolites mediating host–microbiota interactions are currently known. Here, we demonstrate that breastmilk-promoted Bifidobacterium species convert aromatic amino acids (tryptophan, phenylalanine and tyrosine) into their respective aromatic lactic acids (indolelactic acid, phenyllactic acid and 4-hydroxyphenyllactic acid) via a previously unrecognized aromatic lactate dehydrogenase (ALDH). The ability of Bifidobacterium species to convert aromatic amino acids to their lactic acid derivatives was confirmed using monocolonized mice. Longitudinal profiling of the faecal microbiota composition and metabolome of Danish infants (n = 25), from birth until 6 months of age, showed that faecal concentrations of aromatic lactic acids are correlated positively with the abundance of human milk oligosaccharide-degrading Bifidobacterium species containing the ALDH, including Bifidobacterium longum, B. breve and B. bifidum. We further demonstrate that faecal concentrations of Bifidobacterium-derived indolelactic acid are associated with the capacity of these samples to activate in vitro the aryl hydrocarbon receptor (AhR), a receptor important for controlling intestinal homoeostasis and immune responses. Finally, we show that indolelactic acid modulates ex vivo immune responses of human CD4+ T cells and monocytes in a dose-dependent manner by acting as an agonist of both the AhR and hydroxycarboxylic acid receptor 3 (HCA3). Our findings reveal that breastmilk-promoted Bifidobacterium species produce aromatic lactic acids in the gut of infants and suggest that these microbial metabolites may impact immune function in early life