Bernardo S. Reis

Transcriptional reprogramming of mature CD4 + helper T cells generates distinct MHC class II-restricted cytotoxic T lymphocytes

TCRαβ thymocytes differentiate into either CD8αβ+ cytotoxic T lymphocytes or CD4+ helper T cells. This functional dichotomy is controlled by key transcription factors, including the helper T cell master regulator ThPOK, which suppresses the cytolytic program in major histocompatibility complex (MHC) class II–restricted CD4+ thymocytes. ThPOK continues to repress genes of the CD8 lineage in mature CD4+ T cells, even as they differentiate into effector helper T cell subsets. Here we found that the helper T cell fate was not fixed and that mature, antigen-stimulated CD4+ T cells terminated expression of the gene encoding ThPOK and reactivated genes of the CD8 lineage. This unexpected plasticity resulted in the post-thymic termination of the helper T cell program and the functional differentiation of distinct MHC class II–restricted CD4+ cytotoxic T lymphocytes.

Mutual expression of the transcription factors Runx3 and ThPOK regulates intestinal CD4+ T cell immunity

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

Lung dendritic cells induce migration of protective T cells to the gastrointestinal tract

Lung DCs induce the expression of gut-homing molecules on T cells, resulting in their migration to the GI tract and protection against Salmonella infection after immunization

Transcription Factor T-bet Regulates Intraepithelial Lymphocyte Functional Maturation

The intestinal epithelium harbors large populations of activated and memory lymphocytes, yet these cells do not cause tissue damage in the steady state. We investigated how intestinal T cell effector differentiation is regulated upon migration to the intestinal epithelium. Using gene loss- and gain-of-function strategies, as well as reporter approaches, we showed that cooperation between the transcription factors T-bet and Runx3 resulted in suppression of conventional CD4(+) T helper functions and induction of an intraepithelial lymphocyte (IEL) program that included expression of IEL markers such as CD8αα homodimers. Interferon-γ sensing and T-bet expression by CD4(+) T cells were both required for this program, which was distinct from conventional T helper differentiation but shared by other IEL populations, including TCRαβ(+)CD8αα(+) IELs. We conclude that the gut environment provides cues for IEL maturation through the interplay between T-bet and Runx3, allowing tissue-specific adaptation of mature T lymphocytes.

Tissue adaptation of regulatory and intraepithelial CD4+ T cells controls gut inflammation

Location matters for immunosuppression In the gut, food antigens and resident microbes can trigger unwanted immune responses. Immunosuppressive cell types in the gut, such as regulatory T cells (Tregs) and intraepithelial T lymphocytes (IELs), help to keep these responses at bay. Sujino et al. report that the specific anatomical location within the gut shapes the properties of the suppressive T cell populations that reside there (see the Perspective by Colonna and Cervantes-Barragan). Using mice, they find that Tregs primarily reside in the lamina propria. Tregs migrate to the intestinal epithelium, where they convert to IELs in a process that depends on the microbiota and the loss of a specific transcription factor. Tregs and IELs also play distinct but complementary roles in suppressing intestinal inflammation. Science, this issue p. 1581; see also p. 1515 The microenvironment shapes the phenotype and function of suppressive T lymphocyte populations in the gut. Foxp3+ regulatory T cells in peripheral tissues (pTregs) are instrumental in limiting inflammatory responses to nonself antigens. Within the intestine, pTregs are located primarily in the lamina propria, whereas intraepithelial CD4+ T cells (CD4IELs), 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 Tregs and CD4IELs. Upon migration to the epithelium, Tregs lose Foxp3 and convert to CD4IELs in a microbiota-dependent manner, an effect attributed to the loss of the transcription factor ThPOK. Finally, we demonstrate that pTregs and CD4IELs perform complementary roles in the regulation of intestinal inflammation. These results reveal intratissue specialization of anti-inflammatory T cells shaped by discrete niches of the intestine.

Leptin Receptor Signaling in T Cells Is Required for Th17 Differentiation

The hormone leptin plays a key role in energy homeostasis, and the absence of either leptin or its receptor (LepR) leads to severe obesity and metabolic disorders. To avoid indirect effects and to address the cell-intrinsic role of leptin signaling in the immune system, we conditionally targeted LepR in T cells. In contrast with pleiotropic immune disorders reported in obese mice with leptin or LepR deficiency, we found that LepR deficiency in CD4+ T cells resulted in a selective defect in both autoimmune and protective Th17 responses. Reduced capacity for differentiation toward a Th17 phenotype by lepr-deficient T cells was attributed to reduced activation of the STAT3 and its downstream targets. This study establishes cell-intrinsic roles for LepR signaling in the immune system and suggests that leptin signaling during T cell differentiation plays a crucial role in T cell peripheral effector function.

Intestinal Epithelial and Intraepithelial T Cell Crosstalk Mediates a Dynamic Response to Infection

Intestinal intraepithelial lymphocytes (IELs) are located at the critical interface between the intestinal lumen, which is chronically exposed to food and microbes, and the core of the body. Using high-resolution microscopy techniques and intersectional genetic tools, we investigated the nature of IEL responses to luminal microbes. We observed that TCRγδ IELs exhibit unique microbiota-dependent location and movement patterns in the epithelial compartment. This behavioral pattern quickly changes upon exposure to different enteric pathogens, resulting in increased interepithelial cell (EC) scanning, expression of antimicrobial genes, and glycolysis. Both dynamic and metabolic changes to γδ IEL depend on pathogen sensing by ECs. Direct modulation of glycolysis is sufficient to change γδ IEL behavior and susceptibility to early pathogen invasion. Our results uncover a coordinated EC-IEL response to enteric infections that modulates lymphocyte energy utilization and dynamics and supports maintenance of the intestinal epithelial barrier. VIDEO ABSTRACT.

The Role of the Intestinal Context in the Generation of Tolerance and Inflammation

The mucosal surface of the intestine alone forms the largest area exposed to exogenous antigens as well as the largest collection of lymphoid tissue in the body. The enormous amount of nonpathogenic and pathogenic bacteria and food-derived antigens that we are daily exposed sets an interesting challenge to the immune system: a protective immune activity must coexist with efficient regulatory mechanisms in order to maintain a health status of these organisms. This paper discusses how the immune system assimilates the perturbations from the environment without generating tissue damage.

Tissue adaptation: Implications for gut immunity and tolerance

Tissue adaptation is an intrinsic component of immune cell development, influencing both resistance to pathogens and tolerance. Chronically stimulated surfaces of the body, in particular the gut mucosa, are the major sites where immune cells traffic and reside. Their adaptation to these environments requires constant discrimination between natural stimulation coming from harmless microbiota and food, and pathogens that need to be cleared. This review will focus on the adaptation of lymphocytes to the gut mucosa, a highly specialized environment that can help us understand the plasticity of leukocytes arriving at various tissue sites and how tissue-related factors operate to shape immune cell fate and function.

Crucial role for T cell-intrinsic IL-18R-MyD88 signaling in cognate immune response to intracellular parasite infection

MyD88 is the main adaptor molecule for TLR and IL-1R family members. Here, we demonstrated that T-cell intrinsic MyD88 signaling is required for proliferation, protection from apoptosis and expression of activation/memory genes during infection with the intracellular parasite Trypanosoma cruzi, as evidenced by transcriptome and cytometry analyses in mixed bone-marrow (BM) chimeras. The lack of direct IL-18R signaling in T cells, but not of IL-1R, phenocopied the absence of the MyD88 pathway, indicating that IL-18R is a critical MyD88-upstream pathway involved in the establishment of the Th1 response against an in vivo infection, a presently controvert subject. Accordingly, Il18r1−/− mice display lower levels of Th1 cells and are highly susceptible to infection, but can be rescued from mortality by the adoptive transfer of WT CD4+ T cells. Our findings establish the T-cell intrinsic IL-18R/MyD88 pathway as a crucial element for induction of cognate Th1 responses against an important human pathogen.