No abstract

Summary Proper adaptation to environmental perturbations is essential for tissue homeostasis. In the intestine, diverse environmental cues can be sensed by immune cells, which must balance resistance to microorganisms with tolerance, avoiding excess tissue damage. By applying imaging and transcriptional profiling tools, we interrogated how distinct microenvironments in the gut regulate resident macrophages. We discovered that macrophages exhibit a high degree of gene-expression specialization dependent on their proximity to the gut lumen. Lamina propria macrophages (LpMs) preferentially expressed a pro-inflammatory phenotype when compared to muscularis macrophages (MMs), which displayed a tissue-protective phenotype. Upon luminal bacterial infection, MMs further enhanced tissue-protective programs, and this was attributed to swift activation of extrinsic sympathetic neurons innervating the gut muscularis and norepinephrine signaling to β2 adrenergic receptors on MMs. Our results reveal unique intra-tissue macrophage specialization and identify neuro-immune communication between enteric neurons and macrophages that induces rapid tissue-protective responses to distal perturbations.

TCRαβ thymocytes differentiate to either CD8αβ cytotoxic T lymphocytes or CD4+ T helper cells. This functional dichotomy is controlled by key transcription factors, including the T helper master regulator, ThPOK, which suppresses the cytolytic program in MHC class II-restricted CD4+ thymocytes. ThPOK continues to repress CD8-lineage genes in mature CD4+ T cells, even as they differentiate to T helper effector subsets. Here we show that the T helper-fate was not fixed and that mature antigen-stimulated CD4+ T cells could terminate Thpok expression and reactivate CD8-lineage genes. This unexpected plasticity resulted in the post-thymic termination of the T helper-program and the functional differentiation of distinct MHC class II-restricted CD4+ cytotoxic T lymphocytes.

The gut mucosa hosts large numbers of activated lymphocytes, exposed to stimuli from diet, microbiota and pathogens. Although CD4+ T cells are crucial for defense, intestinal homeostasis precludes exaggerated response towards luminal contents, harmful or not. We investigated mechanisms used by CD4+ T cells to avoid excessive activation within the intestine. Using genetic tools to label and interfere with T cell development transcription factors we show that CD4+ T cells acquired CD8-lineage transcription factor Runx3 while losing CD4-lineage transcription factor ThPOK along with their TH17 differentiation and colitogenic potential, in a transforming growth factor-β (TGF-β) and retinoic-acid-dependent manner. These results show a remarkable plasticity in the CD4+ T cell lineage that allows chronic exposure to luminal antigens without pathological inflammation.

Therapeutic harnessing of adaptive immunity via checkpoint inhibition has transformed the treatment of many cancers. Despite unprecedented long-term responses, most patients do not respond to these therapies. Immunotherapy non-responders often harbor high levels of circulating myeloid-derived suppressor cells (MDSCs)-an immunosuppressive innate cell population. Through genetic and pharmacological approaches, we uncovered a pathway governing MDSC abundance in multiple cancer types. Therapeutic liver-X nuclear receptor (LXR) agonism reduced MDSC abundance in murine models and in patients treated in a first-in-human dose escalation phase 1 trial. MDSC depletion was associated with activation of cytotoxic T lymphocyte (CTL) responses in mice and patients. The LXR transcriptional target ApoE mediated these effects in mice, where LXR/ApoE activation therapy elicited robust anti-tumor responses and also enhanced T cell activation during various immune-based therapies. We implicate the LXR/ApoE axis in the regulation of innate immune suppression and as a target for enhancing the efficacy of cancer immunotherapy in patients.

Foxp3 + regulatory T cells in peripheral tissues (pT regs ) are instrumental in limiting inflammatory responses to non-self antigens. Within the intestine, pT regs are located primarily in the lamina propria, while intraepithelial CD4 + T cells (CD4 IELs ), which also exhibit anti-inflammatory properties and depend on similar environmental cues, reside in the epithelium. Using intravital microscopy, we show distinct cell dynamics of intestinal T regs and CD4 IELs . Upon migration to the epithelium, T regs lose Foxp3 and convert to CD4 IELs in a microbiota-dependent fashion, an effect attributed to the loss of the transcription factor ThPOK. Finally, we demonstrate that pT regs and CD4 IELs perform complementary roles in the regulation of intestinal inflammation. These results reveal intra-tissue specialization of anti-inflammatory T cells shaped by discrete niches of the intestine.The gut mucosa is exposed to large amounts of both harmless and potentially pathogenic stimuli on a daily basis, hence diverse immune regulatory mechanisms must operate to avoid inflammatory diseases (1). Peripheral Foxp3-expressing regulatory T cells (pT regs ) mediate suppression of a variety of immune cells and actively prevent inflammatory bowel diseases and food allergies (2-7). Similar to pT regs , Foxp3 − CD8αα + CD4 + intraepithelial lymphocytes (CD4 IELs ) depend on retinoic acid (RA) and transforming growth factor (TGF)-β signaling for their development and also have anti-inflammatory properties (4,(8)(9)(10)(11)(12)(13). However, while CD4 IELs accumulate in the intestinal epithelium, very few total T regs (including pT regs or thymically-derived T regs ) can be found at this site ( fig. S1A and B fig. S2A). Because previous studies have demonstrated that the majority of "ex-Foxp3" cells in the steady state were derived from uncommitted precursors that transiently upregulated Foxp3 (18), we also performed fate mapping after pulse-labeling iFoxp3 Tomato mice with tamoxifen (14), a strategy more likely to target bona fide T regs (19). Nevertheless, while stable Foxp3 expression was again observed in several peripheral tissues examined, over 50% of Tomato + CD4 + T cells that accumulated in the small intestine and almost 10% in the large intestine epithelium isolated from iFoxp3 Tomato mice no longer expressed Foxp3 fives weeks post tamoxifen administration ( fig. S2B and C). The contribution of Tomato + cells to the CD8αα + and CD8αβ + CD4 IEL pools was roughly 10% and 25%, respectively ( fig. S2D). Consistent with a ThPOK-dependent process, ex-T regs that underwent IEL differentiation showed low levels of ThPOK ( fig. S2E). These results indicate that a substantial proportion of intestinal T regs physiologically convert to CD4 IELs .Commensal bacteria play a major role in the induction of lamina propria pT regs in the large intestine (3,(5)(6)(7)20). In contrast, we observed an increased frequency of pT regs (Neuropilin-1 − Foxp3 + ) in the small intestinal epithelium isolated from germ-free (GF) mice when compared to...

The intestinal immune system has the challenging task of tolerating foreign nutrients and the commensal microbiome, while excluding or eliminating ingested pathogens. Failure in such balance leads to severe diseases such as inflammatory bowel diseases (IBD), food allergies or invasive gastrointestinal infections 1 . Multiple immune mechanisms are therefore in place to maintain tissue integrity, including balanced generation of effector T (T H ) cells and FOXP3 + regulatory T (pTreg) cells, which mediate resistance to pathogens and regulate excessive immune activation, respectively 1 – 4 . The gut–draining lymph nodes (gLNs) are critical sites for orchestrating adaptive immunity to luminal perturbations 5 – 7 . However, how they manage to simultaneously support tolerogenic and inflammatory reactions is incompletely understood. Here we report that gLNs are immunologically unique according to the functional gut segment they drain. Stromal and dendritic cell gene signatures as well as T cell polarization against the same luminal antigen differed between gLNs, the proximal small intestine–draining gLNs preferentially giving rise to tolerogenic and the distal gLNs to pro-inflammatory T cell responses. This segregation permitted targeting distal gLNs for vaccination and maintenance of duodenal pTreg cell induction during colonic infection. Conversely, the compartmentalized dichotomy was perturbed by surgical removal of select distal gLNs and duodenal infection, impacting both lymphoid organ and tissue immune responses. Our findings reveal that the conflict between tolerogenic and inflammatory intestinal responses is in part resolved by discrete gLN drainage, and encourage gut segment-specific antigen targeting for therapeutic immune modulation.

Highlights d Enteric pathogens trigger reversible neuronal loss and longterm GI symptoms d Enteric infection-triggered neuronal loss is Nlrp6and caspase 11-dependent d Intestinal muscularis macrophages (MMs) rapidly respond to enteric pathogens d Neuronal death is limited by a MM-b 2 -adrenergic-arginase 1polyamine axis