Bacterial dysbiosis is associated with Crohn’s disease (CD), a chronic intestinal inflammatory disorder thought to result from an abnormal immune response against intestinal bacteria in genetically susceptible individuals. However, it is unclear whether dysbiosis is a cause or consequence of intestinal inflammation and whether overall dysbiosis or specific bacteria trigger the disease. Here, we show that the combined deficiency of NOD2 and phagocyte NADPH oxidase, two CD susceptibility genes, triggers early-onset spontaneous TH1-type intestinal inflammation in mice with the pathological hallmarks of CD. Disease was induced byMucispirillum schaedleri, a Gram-negative mucus-dwelling anaerobe. NOD2 and CYBB deficiencies led to marked accumulation ofMucispirillum, which was associated with impaired neutrophil recruitment and killing of the bacterium by luminal neutrophils. Maternal immunoglobulins againstMucispirillumprotected mutant mice from disease during breastfeeding. Our results indicate that a specific intestinal microbe triggers CD-like disease in the presence of impaired clearance of the bacterium by innate immunity.

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The activation of thymic B cells is critical for their licensing as antigen presenting cells and resulting ability to mediate T cell central tolerance. The processes leading to licensing are still not fully understood. By comparing thymic B cells to activated Peyer’s patch B cells at steady state, we found that thymic B cell activation starts during the neonatal period and is characterized by TCR/CD40-dependent activation, followed by immunoglobulin class switch recombination (CSR) without forming germinal centers. Transcriptional analysis also demonstrated a strong interferon signature, which was not apparent in the periphery. Thymic B cell activation and CSR were primarily dependent on type III IFN signaling, and loss of type III IFN receptor in thymic B cells resulted in reduced thymocyte regulatory T cell (T reg ) development. Finally, from TCR deep sequencing, we estimate that licensed B cells induce development of a substantial fraction of the T reg cell repertoire. Together, these findings reveal the importance of steady-state type III IFN in generating licensed thymic B cells that induce T cell tolerance to activated B cells.

OBJECTIVES/GOALS: Phagocytes, diverse cells that ingest material, are the primary cell type infected by Mycobacterium tuberculosis (Mtb) and the executors of protective mechanisms. T cells play a critical role by helping phagocytes control the infection. Understanding the precise T cell-dependent mechanisms by which phagocytic cell types contain Mtb is critical. METHODS/STUDY POPULATION: To determine the impact T cells have on different phagocyte cell populations’ host defense mechanisms, groups of wild–type and T cell deficient TCRa-/- mice were infected with an Mtb strain expressing fluorescent mScarlet protein. At four weeks post-infection, a time when T cell help contributes to control of Mtb, lungs were homogenized and cells sorted based on detection of mScarlet, indicating Mtb-infected cells. Cell suspensions from each mouse background were underwent single-cell RNA sequencing analysis to reveal the heterogenous cellular transcriptional response of different phagocyte populations. RESULTS/ANTICIPATED RESULTS: We found that Mtb-infected phagocytes from wild-type and TCRa-/- mouse lungs contain the same dominant cell phenotypic clusters, but these have different patterns of gene expression. Without T cells, phagocytes are prone to a more inflammatory phenotype. DISCUSSION/SIGNIFICANCE: This will translate fundamental biological data to test the hypothesis that Mtb encounters different environmental stresses exerted by different phagocytic cell types. This work could reveal host intracellular niches that enable bacterial persistence and elucidate new pathways that could be targeted for traditional antibiotic therapies for TB.