Roles of T cell-associated L-selectin and β7 integrins during induction and regulation of chronic colitis

Chemokinergic and Dopaminergic Signalling Collaborates through the Heteromer Formed by CCR9 and Dopamine Receptor D5 Increasing the Migratory Speed of Effector CD4+ T-Cells to Infiltrate the Colonic Mucosa

Inflammatory bowel diseases (IBDs) involve chronic inflammation of the gastrointestinal tract, where effector CD4+ T-cells play a central role. Thereby, the recruitment of T-cells into the colonic mucosa represents a key process in IBD. We recently found that CCR9 and DRD5 might form a heteromeric complex on the T-cell surface. The increase in CCL25 production and the reduction in dopamine levels associated with colonic inflammation represent a dual signal stimulating the CCR9:DRD5 heteromer, which promotes the recruitment of CD4+ T-cells into the colonic lamina propria. Here, we aimed to analyse the molecular requirements involved in the heteromer assembly as well as to determine the underlying cellular mechanisms involved in the colonic tropism given by the stimulation of the CCR9:DRD5 complex. The results show that dual stimulation of the CCR9:DRD5 heteromer potentiates the phosphorylation of the myosin light chain 2 (MLC2) and the migration speed in confined microchannels. Accordingly, disrupting the CCR9:DRD5 assembly induced a sharp reduction in the pMLC2 in vitro, decreased the migratory speed in confined microchannels, and dampened the recruitment of CD4+ T-cells into the inflamed colonic mucosa. Furthermore, in silico analysis confirmed that the interface of interaction of CCR9:DRD5 is formed by the transmembrane segments 5 and 6 from each protomer. Our findings demonstrated that the CCR9:DRD5 heteromeric complex plays a fundamental role in the migration of CD4+ T-cells into the colonic mucosa upon inflammation. Thereby, the present study encourages the design of strategies for disassembling the formation of the CCR9:DRD5 as a therapeutic opportunity to treat IBD.

The role of T-lymphocytes in central nervous system diseases

The central nervous system (CNS) has been considered an immunologically privileged site. In the past few decades, research on inflammation in CNS diseases has mostly focused on microglia, innate immune cells that respond rapidly to injury and infection to maintain CNS homeostasis. Discoveries of lymphatic vessels within the dura mater and peripheral immune cells in the meningeal layer indicate that the peripheral immune system can monitor and intervene in the CNS. This review summarizes recent advances in the involvement of T lymphocytes in multiple CNS diseases, including brain injury, neurodegenerative diseases, and psychiatric disorders. It emphasizes that a deep understanding of the pathogenesis of CNS diseases requires intimate knowledge of T lymphocytes. Aiming to promote a better understanding of the relationship between the immune system and CNS and facilitate the development of therapeutic strategies targeting T lymphocytes in neurological diseases.

The Heteromeric Complex Formed by Dopamine Receptor D5 and CCR9 Leads the Gut Homing of CD4+ T Cells Upon Inflammation

BACKGROUND AND AIMS

CD4+ T cells constitute central players in inflammatory bowel diseases (IBDs), driving inflammation in the gut mucosa. Current evidence indicates that CCR9 and the integrin α4β7 are necessary and sufficient to imprint colonic homing on CD4+ T cells upon inflammation. Interestingly, dopaminergic signaling has been previously involved in leukocyte homing. Despite dopamine levels are strongly reduced in the inflamed gut mucosa, the role of dopamine in the gut homing of T cells remains unknown. Here, we study how dopaminergic signaling affects T cells upon gut inflammation.

METHODS

Gut inflammation was induced by transfer of naïve T cells into Rag1-/- mice or by administration of dextran sodium sulfate. T cell migration and differentiation were evaluated by adoptive transfer of congenic lymphocytes followed by flow cytometry analysis. Protein interaction was studied by bioluminescence resonance energy transfer analysis, bimolecular fluorescence complementation, and in situ proximity ligation assays.

RESULTS

We show the surface receptor providing colonic tropism to effector CD4+ T cells upon inflammation is not CCR9 but the complex formed by CCR9 and the dopamine receptor D5 (DRD5). Assembly of the heteromeric complex was demonstrated in vitro and in vivo using samples from mouse and human origin. The CCR9:DRD5 heteroreceptor was upregulated in the intestinal mucosa of IBD patients. Signaling assays confirmed that complexes behave differently than individual receptors. Remarkably, the disruption of CCR9:DRD5 assembly attenuated the recruitment of CD4+ T cells into the colonic mucosa.

CONCLUSIONS

Our findings describe a key homing receptor involved in gut inflammation and introduce a new cell surface module in immune cells: macromolecular complexes formed by G protein-coupled receptors integrating the sensing of multiple molecular cues.

Activation of Peripheral Blood CD4+ T-Cells in IBS is not Associated with Gastrointestinal or Psychological Symptoms

Immune activation may underlie the pathogenesis of irritable bowel syndrome (IBS), but the evidence is conflicting. We examined whether peripheral CD4+ T-cells from IBS patients demonstrated immune activation and changes in cytokine production. To gain mechanistic insight, we examined whether immune activation correlated with psychological stress and changing symptoms over time. IBS patients (n = 29) and healthy volunteers (HV; n = 29) completed symptom and psychological questionnaires. IBS patients had a significant increase in CD4+ T-cells expressing the gut homing marker integrin β7 (p = 0.023) and lymphoid marker CD62L (p = 0.026) compared to HV. Furthermore, phytohaemagglutinin stimulated CD4+ T-cells from IBS-D patients demonstrated increased TNFα secretion when compared to HV (p = 0.044). Increased psychological scores in IBS did not correlate with TNFα production, while stress hormones inhibited cytokine secretion from CD4+ T-cells of HV in vitro. IBS symptoms, but not markers of immune activation, decreased over time. CD4+ T-cells from IBS-D patients exhibit immune activation, but this did not appear to correlate with psychological stress measurements or changing symptoms over time. This could suggest that immune activation is a surrogate of an initial trigger and/or ongoing parallel peripheral mechanisms.

T-Cell-Driven Inflammation as a Mediator of the Gut-Brain Axis Involved in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder affecting mainly the dopaminergic neurons of the nigrostriatal pathway, a neuronal circuit involved in the control of movements, thereby the main manifestations correspond to motor impairments. The major molecular hallmark of this disease corresponds to the presence of pathological protein inclusions called Lewy bodies in the midbrain of patients, which have been extensively associated with neurotoxic effects. Importantly, different research groups have demonstrated that CD4⁺ T-cells infiltrate into the substantia nigra of PD patients and animal models. Moreover, several studies have consistently demonstrated that T-cell deficiency results in a strong attenuation of dopaminergic neurodegeneration in animal models of PD, thus indicating a key role of adaptive immunity in the neurodegenerative process. Recent evidence has shown that CD4⁺ T-cell response involved in PD patients is directed to oxidised forms of α-synuclein, one of the main constituents of Lewy bodies. On the other hand, most PD patients present a number of non-motor manifestations. Among non-motor manifestations, gastrointestinal dysfunctions result especially important as potential early biomarkers of PD, since they are ubiquitously found among confirmed patients and occur much earlier than motor symptoms. These gastrointestinal dysfunctions include constipation and inflammation of the gut mucosa and the most distinctive pathologic features associated are the loss of neurons of the enteric nervous system and the generation of Lewy bodies in the gut. Moreover, emerging evidence has recently shown a pivotal role of gut microbiota in triggering the development of PD in genetically predisposed individuals. Of note, PD has been positively correlated with inflammatory bowel diseases, a group of disorders involving a T-cell driven inflammation of gut mucosa, which is strongly dependent in the composition of gut microbiota. Here we raised the hypothesis that T-cell driven inflammation, which mediates dopaminergic neurodegeneration in PD, is triggered in the gut mucosa. Accordingly, we discuss how structural components of commensal bacteria or how different mediators produced by gut-microbiota, including short-chain fatty acids and dopamine, may affect the behaviour of T-cells, triggering the development of T-cell responses against Lewy bodies, initially confined to the gut mucosa but later extended to the brain.

Suppression of Th17 Cell Response in the Alleviation of Dextran Sulfate Sodium-Induced Colitis by Ganoderma lucidum Polysaccharides

Background

Ganoderma lucidum polysaccharides (GLP) has anti-inflammatory and immunomodulatory effects. Dysregulated immune responses are involved in the pathogenesis of dextran sulfate sodium (DSS)-induced colitis. The aim of this study was to assess the therapeutic potential of GLP to alleviate DSS-induced colitis.

Methods

The mice were administered with GLP by intragastric gavage daily for two weeks prior to the DSS treatment. Mice were orally administered with 2.5% DSS dissolved in drinking water with GLP or water treatment for 6 days. The mice were killed on day 7 after induction of colitis. Survival rates, body weight loss, colon lengths, histological changes, and disease activity index scores (DAI) were evaluated.

Results

GLP significantly improved survival rates, colon length shortening, body weight loss, histopathological score, and DAI scores in mice with DSS-induced colitis. GLP markedly suppressed the secretions of TNF-α, IL-1β, IL-6, IL-17A, and IL-4 and significantly affected populations of Th17 cells, B cells, NK cells, and NKT cells in the lamina propria lymphocytes.

Conclusions

GLP prevented inflammation, maintained intestinal homeostasis, and regulated the intestinal immunological barrier functions in mice with DSS-induced colitis.

A Critical Role for Monocytes/Macrophages During Intestinal Inflammation-associated Lymphangiogenesis

BACKGROUND

Inflammation-associated lymphangiogenesis (IAL) is frequently observed in inflammatory bowel diseases. IAL is believed to limit inflammation by enhancing fluid and immune cell clearance. Although monocytes/macrophages (MΦ) are known to contribute to intestinal pathology in inflammatory bowel disease, their role in intestinal IAL has never been studied mechanistically. We investigated contributions of monocytes/MΦ to the development of intestinal inflammation and IAL.

METHODS

Because inflammatory monocytes express CC chemokine receptor 2 (CCR2), we used CCR2 diphtheria toxin receptor transgenic (CCR2.DTR) mice, in which monocytes can be depleted by diphtheria toxin injection, and CCR2 mice, which have reduced circulating monocytes. Acute or chronic colitis was induced by dextran sodium sulfate or adoptive transfer of CD4CD45RB T cells, respectively. Intestinal inflammation was assessed by flow cytometry, immunofluorescence, disease activity, and histopathology, whereas IAL was assessed by lymphatic vessel morphology and density.

RESULTS

We demonstrated that intestinal MΦ expressed vascular endothelial growth factor-C/D. In acute colitis, monocyte-depleted mice were protected from intestinal injury and showed reduced IAL, which was reversed after transfer of wild-type monocytes into CCR2 mice. In chronic colitis, CCR2 deficiency did not attenuate inflammation but reduced IAL.

CONCLUSIONS

We propose a dual role of MΦ in (1) promoting acute inflammation and (2) contributing to IAL. Our data suggest that intestinal inflammation and IAL could occur independently, because IAL was reduced in the absence of monocytes/MΦ, even when inflammation was present. Future inflammatory bowel disease therapies might exploit promotion of IAL and suppression of MΦ independently, to restore lymphatic clearance and reduce inflammation.

β7-Integrin exacerbates experimental DSS-induced colitis in mice by directing inflammatory monocytes into the colon

Leukocyte recruitment is pivotal for the initiation and perpetuation of inflammatory bowel disease (IBD) and controlled by the specificity and interactions of chemokines and adhesion molecules. Interactions of the adhesion molecules α4β7-integrin and mucosal addressin cell-adhesion molecule-1 (MAdCAM-1) promote the accumulation of pathogenic T-cell populations in the inflamed intestine. We aimed to elucidate the significance of β7-integrin expression on innate immune cells for the pathogenesis of IBD. We demonstrate that β7-integrin deficiency protects recombination-activating gene-2 (RAG-2)-deficient mice from dextran sodium sulfate (DSS)-induced colitis and coincides with decreased numbers of colonic effector monocytes. We also show that β7-integrin is expressed on most CD11b(+)CD64(low)Ly6C(+) bone marrow progenitors and contributes to colonic recruitment of these proinflammatory monocytes. Importantly, adoptive transfer of CD115(+) wild-type (WT) monocytes partially restored the susceptibility of RAG-2/β7-integrin double-deficient mice to DSS-induced colitis, thereby demonstrating the functional importance of β7-integrin-expressing monocytes for the development of DSS colitis. We also reveal that genetic ablation of MAdCAM-1 ameliorates experimental colitis in RAG-2-deficient mice as well. In summary, we demonstrate a previously unknown role of α4β7-integrin-MAdCAM-1 interactions as drivers of colitis by directing inflammatory monocytes into the colon.

T cell-associated α4β7 but not α4β1 integrin is required for the induction and perpetuation of chronic colitis

Anti-adhesion therapies that target α(4) integrins (e.g., natalizumab) are thought to work by blocking T-cell recruitment to the intestinal tissues in patients with Crohn's disease (CD); however, little direct evidence is available to confirm this contention. We wished to evaluate the importance of T cell-associated α(4) integrins in a chronic colitis model in mice and to determine the effect of natalizumab treatment on intestinal tissue T-cell accumulation in human CD. Adoptive transfer of T cells lacking α(4) (α(4)(-/-)) but not β(1) integrin into immunodeficient mice produced significantly attenuated disease. This was correlated with reduced numbers of colon CD4 T cells compared with the control mice; however, tissue distribution of T helper type 1 (Th1) and T helper type 17 (Th17) cells and regulatory T cells (Tregs) was not affected by the lack of α(4). Furthermore, α(4)(-/-) T cells demonstrated defective homing to the chronically inflamed small intestines and colons. Finally, patients treated with natalizumab showed significant reduction in mucosal CD4 T cells and no skewing in the foxp3(+) Treg or T-bet(+)Th1 fractions thereof. These results demonstrate a direct role for T cell-associated α(4)β(7) but not α(4)β(1) integrins during initiation and perpetuation of chronic colitis. Moreover, our data demonstrated that natalizumab treatment reduced mucosal CD4 T-cell accumulation in CD patients.