Signalling mechanisms driving homeostatic and inflammatory effects of interleukin-15 on tissue lymphocytes

There is an intriguing dichotomy in the function of cytokine interleukin-15-at low levels, it is required for the homeostasis of the immune system, yet when it is upregulated in response to pathogenic infections or in autoimmunity, IL-15 drives inflammation. IL-15 associates with the IL-15Rα within both myeloid and non-haematopoietic cells, where IL-15Rα trans-presents IL-15 in a membrane-bound form to neighboring cells. Alongside homeostatic maintenance of select lymphocyte populations such as NK cells and tissue-resident T cells, when upregulated, IL-15 also promotes inflammatory outcomes by driving effector function and cytotoxicity in NK cells and T cells. As chronic over-expression of IL-15 can lead to autoimmunity, IL-15 expression is tightly regulated. Thus, blocking dysregulated IL-15 and its downstream signalling pathways are avenues for immunotherapy. In this review we discuss the molecular pathways involved in IL-15 signalling and how these pathways contribute to both homeostatic and inflammatory functions in IL-15-dependent mature lymphoid populations, focusing on innate, and innate-like lymphocytes in tissues.</p

Signalling mechanisms driving homeostatic and inflammatory effects of interleukin-15 on tissue lymphocytes

There is an intriguing dichotomy in the function of cytokine interleukin-15-at low levels, it is required for the homeostasis of the immune system, yet when it is upregulated in response to pathogenic infections or in autoimmunity, IL-15 drives inflammation. IL-15 associates with the IL-15Rα within both myeloid and non-haematopoietic cells, where IL-15Rα trans-presents IL-15 in a membrane-bound form to neighboring cells. Alongside homeostatic maintenance of select lymphocyte populations such as NK cells and tissue-resident T cells, when upregulated, IL-15 also promotes inflammatory outcomes by driving effector function and cytotoxicity in NK cells and T cells. As chronic over-expression of IL-15 can lead to autoimmunity, IL-15 expression is tightly regulated. Thus, blocking dysregulated IL-15 and its downstream signalling pathways are avenues for immunotherapy. In this review we discuss the molecular pathways involved in IL-15 signalling and how these pathways contribute to both homeostatic and inflammatory functions in IL-15-dependent mature lymphoid populations, focusing on innate, and innate-like lymphocytes in tissues.</p

Nanocomplejos del receptor para el antígeno de linfocitos T: agruparse para cooperar

The T cell antigen receptor (TCR·CD3) is a multi-subunit complex responsible for triggering an adaptive immune response. It shows high specificity and sensitivity while having a low affinity for the ligand. Furthermore, T cells respond to antigen over a wide concentration range. The stoichiometry and architecture of TCR·CD3 in the membrane have been under intense scrutiny because they might be key to explaining its paradoxical properties. This review highlights new evidence that TCR·CD3 is found on intact, unstimulated T cells in monovalent (one ligand-binding site per receptor) as well as in several distinct multivalent forms. This is in contrast to the TCR·CD3 stoichiometries determined by several biochemical means, but these data can be explained by the effects of different detergents on the integrity of the receptor. Here, we discuss a model in which the multivalent receptors are important for the detection of low concentrations of ligand, and therefore confer sensitivity, whereas the co-expressed monovalent TCR·CD3s allow a wide dynamic range.Key Words: Stoichiometry, Conformational change, T cell antigen receptor, Signal transduction, Transmembrane interactions

Rewiring of the TCR signalosome in natural intestinal Intraepithelial T lymphocytes drives non-deletional tolerance

Intraepithelial T lymphocytes (T-IEL) are a large population of cytotoxic T cells that protect the small intestinal epithelium against pathogens. Based on ontogeny, T-IEL can be categorized into two major subsets: induced and natural. Natural T-IEL are agonistically selected in the thymus on self-antigens before migrating directly to the small intestine. Despite having self-reactive T cell antigen receptors (TCR), natural T-IEL are maintained in a tolerized state in the gut by unknown mechanisms. We therefore investigated TCR signaling in T-IEL using multiplexed fluorescent cell barcoding, phosphoproteomics and TCR signaling reporter mouse models, which revealed that TCR signaling is intrinsically suppressed in natural, but not induced, T-IEL. Unexpectedly, we discover that this cell intrinsic suppression was mediated through altered TCR signalosome components. Specifically, downregulation of the key signaling adaptor, Linker for activation of T cells (LAT) during thymic selection is a vital checkpoint for the development and tolerization of natural IELs. Thus, TCR signaling is rewired in self-reactive natural T-IEL to promote tolerance and prevent inappropriate inflammation in the gut.One sentence summary Self-reactive natural intestinal intraepithelial T lymphocytes are developmentally tolerized by rewiring the T cell antigen receptor signaling pathway through the downregulation of the adaptor protein, LAT

Rewiring of the TCR signalosome in natural intestinal Intraepithelial T lymphocytes drives non-deletional tolerance

Intraepithelial T lymphocytes (T-IEL) are a large population of cytotoxic T cells that protect the small intestinal epithelium against pathogens. Based on ontogeny, T-IEL can be categorized into two major subsets: induced and natural. Natural T-IEL are agonistically selected in the thymus on self-antigens before migrating directly to the small intestine. Despite having self-reactive T cell antigen receptors (TCR), natural T-IEL are maintained in a tolerized state in the gut by unknown mechanisms. We therefore investigated TCR signaling in T-IEL using multiplexed fluorescent cell barcoding, phosphoproteomics and TCR signaling reporter mouse models, which revealed that TCR signaling is intrinsically suppressed in natural, but not induced, T-IEL. Unexpectedly, we discover that this cell intrinsic suppression was mediated through altered TCR signalosome components. Specifically, downregulation of the key signaling adaptor, Linker for activation of T cells (LAT) during thymic selection is a vital checkpoint for the development and tolerization of natural IELs. Thus, TCR signaling is rewired in self-reactive natural T-IEL to promote tolerance and prevent inappropriate inflammation in the gut.One sentence summary Self-reactive natural intestinal intraepithelial T lymphocytes are developmentally tolerized by rewiring the T cell antigen receptor signaling pathway through the downregulation of the adaptor protein, LAT

Tissue environment, not ontogeny, defines murine intestinal intraepithelial T lymphocytes

Tissue-resident intestinal intraepithelial T lymphocytes (T-IEL) patrol the gut and have important roles in regulating intestinal homeostasis. T-IEL include both induced T-IEL, derived from systemic antigen-experienced lymphocytes, and natural T-IEL, which are developmentally targeted to the intestine. While the processes driving T-IEL development have been elucidated, the precise roles of the different subsets and the processes driving activation and regulation of these cells remain unclear. To gain functional insights into these enigmatic cells, we used high-resolution, quantitative mass spectrometry to compare the proteomes of induced T-IEL and natural T-IEL subsets, with naive CD8(+) T cells from lymph nodes. This data exposes the dominant effect of the gut environment over ontogeny on T-IEL phenotypes. Analyses of protein copy numbers of >7000 proteins in T-IEL reveal skewing of the cell surface repertoire towards epithelial interactions and checkpoint receptors; strong suppression of the metabolic machinery indicating a high energy barrier to functional activation; upregulated cholesterol and lipid metabolic pathways, leading to high cholesterol levels in T-IEL; suppression of T cell antigen receptor signalling and expression of the transcription factor TOX, reminiscent of chronically activated T cells. These novel findings illustrate how T-IEL integrate multiple tissue-specific signals to maintain their homeostasis and potentially function

Stoichiometry and intracellular fate of TRIM-containing TCR complexes

<p>Abstract</p> <p>Background</p> <p>Studying the stoichiometry and intracellular trafficking of the T cell antigen receptor (TCR) is pivotal in understanding its mechanisms of activation. The αβTCR includes the antigen-binding TCRαβ heterodimer as well as the signal transducing CD3εγ, CD3εδ and ζ₂subunits. Although the TCR-interacting molecule (TRIM) is also part of the αβTCR complex, it has not been included in most reports so far.</p> <p>Results</p> <p>We used the native antibody-based mobility shift (NAMOS) assay in a first dimension (1D) blue native (BN)-PAGE and a 2D BN-/BN-PAGE to demonstrate that the stoichiometry of the digitonin-solublized TRIM-containing αβTCR is TCRαβCD3ε₂γδζ₂TRIM₂. Smaller αβTCR complexes possess a TCRαβ CD3ε₂γδζ₂stoichiometry. Complexes of these sizes were detected in T cell lines as well as in primary human and mouse T cells. Stimulating the αβTCR with anti-CD3 antibodies, we demonstrate by confocal laser scanning microscopy that CD3ε colocalizes with ζ and both are degraded upon prolonged stimulation, possibly within the lysosomal compartment. In contrast, a substantial fraction of TRIM does not colocalize with ζ. Furthermore, TRIM neither moves to lysosomes nor is degraded. Immunoprecipitation studies and BN-PAGE indicate that TRIM also associates with the γδTCR.</p> <p>Conclusions</p> <p>Small αβTCR complexes have a TCRαβ CD3ε₂γδζ₂stoichiometry; whereas those associated with one TRIM dimer are TCRαβ CD3ε₂γδζ₂TRIM₂. TRIM is differentially processed compared to CD3 and ζ subunits after T cell activation and is not degraded. The γδTCR also associates with TRIM.</p

IL-15 and PIM kinases direct the metabolic programming of intestinal intraepithelial lymphocytes

Intraepithelial lymphocytes (IEL) respond to IL-15 complexed with IL-15Ra but how this intrinsically affects IEL is unclear. Here the authors use proteomics analyses of the main mouse IEL subsets and identify PIM kinases as essential for IEL proliferation, metabolism and effector function downstream of IL-15

Intestinal intraepithelial lymphocyte activation promotes innate antiviral resistance.

Unrelenting environmental challenges to the gut epithelium place particular demands on the local immune system. In this context, intestinal intraepithelial lymphocytes (IEL) compose a large, highly conserved T cell compartment, hypothesized to provide a first line of defence via cytolysis of dysregulated intestinal epithelial cells (IEC) and cytokine-mediated re-growth of healthy IEC. Here we show that one of the most conspicuous impacts of activated IEL on IEC is the functional upregulation of antiviral interferon (IFN)-responsive genes, mediated by the collective actions of IFNs with other cytokines. Indeed, IEL activation in vivo rapidly provoked type I/III IFN receptor-dependent upregulation of IFN-responsive genes in the villus epithelium. Consistent with this, activated IEL mediators protected cells against virus infection in vitro, and pre-activation of IEL in vivo profoundly limited norovirus infection. Hence, intraepithelial T cell activation offers an overt means to promote the innate antiviral potential of the intestinal epithelium.Support was provided by the Wellcome Trust (A.C.H., J.L.H., G.R) and Cancer Research UK (A.C.H.), Department of Health via the National Institute for Health Research (NIHR) comprehensive Biomedical Research Centre award to Guy’s & St Thomas’ NHS Foundation Trust (L.A.-D.; A.C.H.); Marie Curie and EMBO fellowships (M.S.).This is the final published version. It first appeared at http://www.nature.com/ncomms/2015/150519/ncomms8090/full/ncomms8090.html