Immunosenescent colitogenic CD4(+) T cells convert to regulatory cells and suppress colitis

Senescent T cells: Beneficial and detrimental roles

As the thymus involutes during aging, the T-cell pool has to be maintained by the periodic expansion of preexisting T cells during adulthood. A conundrum is that repeated episodes of activation and proliferation drive the differentiation of T cells toward replicative senescence, due to telomere erosion. This review discusses mechanisms that regulate the end-stage differentiation (senescence) of T cells. Although these cells, within both CD4 and CD8 compartments, lose proliferative activity after antigen-specific challenge, they acquire innate-like immune function. While this may confer broad immune protection during aging, these senescent T cells may also cause immunopathology, especially in the context of excessive inflammation in tissue microenvironments.

Regulatory T cells in inflammation and resolution of acute lung injury

Introduction

Acute respiratory distress syndrome (ARDS) is characterized by hypoxemia and increased lung permeability and would result in acute respiratory failure and with high mortality. In patients who survive from acute lung injury (ALI)/ARDS, it is an active process of the transition from injury to resolution depending on the coordinated immune system. The roles of regulatory CD4⁺T cells (Tregs) are now gradually being clarified during inflammation and resolution of ARDS. However, clear conclusions about roles of Tregs in ALI/ARDS are only a few.

Objective

This review provides an overview of phenotype, differentiation, and suppressive mechanisms of Tregs and focuses on keys of biology of Tregs in alveolar space during the inflammatory response and resolution of ALI/ARDS.

Data Source

Literature search of Web of Science, PubMed, and EMBASE was made to find relative articles about Tregs in ALI/ARDS. We used the following search terms: Tregs, ALI, ARDS, inflammation, and resolution.

Conclusion

More and more studies have indicated Tregs involved in the processes of inflammation and resolution of ALI/ARDS. A deep understanding of the roles of Tregs may indicate new treatments for patients of ARDS. Therapies aimed at expansion or adaptive transfer of Tregs could be an effective therapy to ARDS patients.

Metformin ameliorates chronic colitis in a mouse model by regulating interferon-γ-producing lamina propria CD4+ T cells through AMPK activation

Metformin, a commonly prescribed drug for type 2 diabetes mellitus, has been shown to activate AMP-activated protein kinase (AMPK). Notably, AMPK activation has recently been observed to be associated with anti-inflammatory responses. Metformin is also reported to elicit anti-inflammatory responses in CD4+ T cells, resulting in improvement in experimental chronic inflammatory diseases, such as systemic lupus erythematosus. To investigate the effect of metformin on inflammatory bowel disease (IBD), we developed a T cell-transfer model of chronic colitis in which SCID mice were injected with CD4+ CD45RBhigh T cells to induce colitis. We examined the effects of metformin via in vitro and in vivo experiments on lamina propria (LP) CD4+ T cells. We observed that metformin suppresses the frequency of interferon (IFN) -γ-producing LP CD4+ T cells in vitro, which were regulated by AMPK activation, a process possibly induced by the inhibition of oxidative phosphorylation. Furthermore, we examined the effects of metformin on an in vivo IBD model. Metformin-treated mice showed AMPK activation in LP CD4+ T cells and ameliorated colitis. Our study demonstrates that metformin-induced AMPK activation in mucosal CD4+ T cells contributes to the improvement of IBD by suppressing IFN-γ production. Moreover, our results indicate that AMPK may be a target molecule for the regulation of mucosal immunity and inflammation. Thus, AMPK-activating drugs such as metformin may be potential therapeutic agents for the treatment of IBD.

Distribution of mucosal PD-1 expressing T cells in patients with colitis of different etiologies

BACKGROUND

Immunotherapy, targeting programmed death-1 (PD-1) enhances antitumor T-cell activity in patients with malignancies. Blocking PD-1 or its ligand may lead to fulminant colitis as serious adverse event in these patients. Since little is known of the presence and role of PD-1⁺T cells in colitis of different etiologies, we determined PD-1⁺T cells in mucosal specimens of patients with inflammatory bowel disease, infectious colitis (InfC), immunotherapy-related colitis (ImC) and healthy controls (HC).

METHODS

Newly diagnosed patients with ulcerative colitis (UC, n = 73), Crohn's disease (CD, n = 50), InfC (n = 5), ImC (n = 8) and HC (n = 8) were included. Baseline inflamed colonic biopsies were studied with immunohistochemistry and flowcytometry.

RESULTS

Using immunohistochemistry, PD-1 was not present on lymphocytes in the epithelium of all patients, nor in HC. The percentage PD-1⁺ of all lymphocytes in the lamina propria was 40% in UC, 5% in InfC, 3% in ImC and 0% in HC. Flowcytometry showed significant higher percentages of PD-1⁺T cells in inflamed biopsy specimens of UC patients (22%) compared to all other groups: CD patients (13%), InfC (12%), ImC (5%) and HC (6%).

CONCLUSION

There are relevant differences in distribution and frequencies of mucosal PD-1⁺ T-cell subsets in patients with UC, CD, InfC and ImC, supporting the hypothesis that these types of colitis are driven by different immunological pathways. The increased numbers of PD-1⁺ and PD-L1⁺ lymphocytes in the colonic mucosa of UC patients suggest that the PD-1/PD-L1 pathway might be more activated in UC than in CD.

IRF5 Acts as a Potential Therapeutic Marker in Inflammatory Bowel Diseases

BACKGROUND

Inflammatory bowel diseases (IBDs), including ulcerative colitis (UC) and Crohn's disease (CD), are chronic inflammatory disorders. As is well known, interferon regulatory factor (IRF) 5 is closely associated with the pathogenesis of various inflammatory diseases. But the exact role of IRF5 in IBD remains unclear.

METHODS

In this study, we detected IRF5 expression in peripheral blood mononuclear cells (PBMCs) and inflamed mucosa from IBD patients by immunohistochemistry, western blot, and quantitative real-time polymerase chain reaction. Peripheral blood CD4+ T cells were stimulated with inflammatory cytokines and transfected by lentivirus.

RESULTS

In active IBD patients, the expression of IRF5 in PBMCs and inflamed colonic tissues was obviously increased and significantly associated with disease activity. Ectopic overexpression of IRF5 could promote the differentiation of IBD CD4+ T cells into Th1 and Th17 cells by regulating T-bet and RAR related orphan receptor C, whereas knockdown of IRF5 had the opposite effects. Tumor necrosis factor (TNF)-α upregulated expression of IRF5 in CD4+ T cells, but anti-TNF treatment with infliximab could markedly reduce IRF5 expression in CD4+ T cells and intestinal mucosa of CD patients.

CONCLUSION

Our study reveals a novel mechanism that IRF5 levels are correlated with disease activity in IBD and might function as a possible marker for the management of IBD via regulating Th1 and Th17 immune responses and cytokine production.

Role of PD-L1 in Gut Mucosa Tolerance and Chronic Inflammation

The gastrointestinal (GI) mucosa is among the most complex systems in the body. It has a diverse commensal microbiome challenged continuously by food and microbial components while delivering essential nutrients and defending against pathogens. For these reasons, regulatory cells and receptors are likely to play a central role in maintaining the gut mucosal homeostasis. Recent lessons from cancer immunotherapy point out the critical role of the B7 negative co-stimulator PD-L1 in mucosal homeostasis. In this review, we summarize the current knowledge supporting the critical role of PD-L1 in gastrointestinal mucosal tolerance and how abnormalities in its expression and signaling contribute to gut inflammation and cancers. Abnormal expression of PD-L1 and/or the PD-1/PD-L1 signaling pathways have been observed in the pathology of the GI tract. We also discuss the current gap in our knowledge with regards to PD-L1 signaling in the GI tract under homeostasis and pathology. Finally, we summarize the current understanding of how this pathway is currently targeted to develop novel therapeutic approaches.

Berberine Administration in Treatment of Colitis: A Review

Berberine (Brb) is one of the well-known naturally occurring compounds exclusively found in Berberis vulgaris and other members of this family, such as Berberis aristata, Berberis aroatica, and Berberis aquifolium. This plant-derived natural compound has a variety of therapeutic impacts, including anti-oxidant, anti-inflammatory, anti-diabetic, and anti-tumor. Multiple studies have demonstrated that Brb has great anti-inflammatory activity and is capable of reducing the levels of proinflammatory cytokines, while it enhances the concentrations of anti-inflammatory cytokines, making it suitable for the treatment of inflammatory disorders. Colitis is an inflammatory bowel disease with chronic nature. Several factors are involved in the development of colitis and it appears that inflammation and oxidative stress are the most important ones. With respect to the anti-inflammatory and antioxidant effects of Brb, its administration seems to be beneficial in the treatment of colitis. In the present review, the protective effects of Brb in colitis treatment and its impact on molecular pathways are discussed.

Berberine improved experimental chronic colitis by regulating interferon-γ- and IL-17A-producing lamina propria CD4+ T cells through AMPK activation

The herbal medicine berberine (BBR) has been recently shown to be an AMP-activated protein kinase (AMPK) productive activator with various properties that induce anti-inflammatory responses. We investigated the effects of BBR on the mechanisms of mucosal CD4⁺T cell activation in vitro and on the inflammatory responses in T cell transfer mouse models of inflammatory bowel disease (IBD). We examined the favorable effects of BBR in vitro, using lamina propria (LP) CD4⁺ T cells in T cell transfer IBD models in which SCID mice had been injected with CD4⁺CD45RB^high T cells. BBR suppressed the frequency of IFN-γ- and Il-17A-producing LP CD4⁺ T cells. This effect was found to be regulated by AMPK activation possibly induced by oxidative phosphorylation inhibition. We then examined the effects of BBR on the same IBD models in vivo. BBR-fed mice showed AMPK activation in the LPCD4⁺ T cells and an improvement of colitis. Our study newly showed that the BBR-induced AMPK activation of mucosal CD4⁺ T cells resulted in an improvement of IBD and underscored the importance of AMPK activity in colonic inflammation.

Expression of Programmed Death-Ligand 1 by Human Colonic CD90+ Stromal Cells Differs Between Ulcerative Colitis and Crohn's Disease and Determines Their Capacity to Suppress Th1 Cells

Background and Aims

The role of programmed cell death protein 1 (PD-1) and its ligands in the dysregulation of T helper immune responses observed in the inflammatory bowel disease (IBD) is unclear. Recently, a novel concept emerged that CD90⁺ colonic (myo)fibroblasts (CMFs), also known as stromal cells, act as immunosuppressors, and are among the key regulators of acute and chronic inflammation. The objective of this study was to determine if the level of the PD-1 ligands is changed in the IBD inflamed colonic mucosa and to test the hypothesis that changes in IBD-CMF-mediated PD-1 ligand-linked immunosuppression is a mechanism promoting the dysregulation of Th1 cell responses.

Methods

Tissues and cells derived from Crohn's disease (CD), ulcerative colitis (UC), and healthy individuals (N) were studied in situ, ex vivo, and in culture.

Results

A significant increase in programmed death-ligand 1 (PD-L1) was observed in the inflamed UC colonic mucosa when compared to the non-inflamed matched tissue samples, CD, and healthy controls. UC-CMFs were among the major populations in the colonic mucosa contributing to the enhanced PD-L1 expression. In contrast, PD-L1 expression was decreased in CD-CMFs. When compared to CD-CMFs and N-CMFs, UC-CMFs demonstrated stronger suppression of IL-2, Th1 transcriptional factor Tbet, and IFN-γ expression by CD3/CD28-activated CD4⁺ T cells, and this process was PD-L1 dependent. Similar observations were made when differentiated Th1 cells were cocultured with UC-CMFs. In contrast, CD-CMFs showed reduced capacity to suppress Th1 cell activity and addition of recombinant PD-L1 Fc to CD-CMF:T cell cocultures partially restored the suppression of the Th1 type responses.

Conclusion

We present evidence showing that increased PD-L1 expression suppresses Th1 cell activity in UC. In contrast, loss of PD-L1 expression observed in CD contributes to the persistence of the Th1 inflammatory milieu in CD. Our data suggest that dysregulation of the Th1 responses in the inflamed colonic mucosa of IBD patients is promoted by the alterations in PD-L1 expression in the mucosal mesenchymal stromal cell compartment.

PD-1/PD-L and autoimmunity: A growing relationship

Programmed death 1 (PD-1) and its ligands, namely PD-L1 and PD-L2, are one of the key factors responsible for inhibitory T cell signaling, mediating the mechanisms of tolerance and providing immune homeostasis. Mounting evidence demonstrates that impaired PD-1:PD-L function plays an important role in a variety of autoimmune diseases such as Type 1 diabetes (T1D), encephalomyelitis, inflammatory bowel diseases (IBD), Rheumatoid Arthritis (RA), autoimmune hepatitis (AIH), Behcet's disease (BD), myasthenia gravis (MG), autoimmune uveitis (AU), Sjögren's syndrome (SjS), systemic lupus erythematosus (SLE), systemic sclerosis (SSc), myocarditis, and ankylosing spondylitis (AS). By investigating the candidate genes, genome-wide association studies, and identification of single nucleotide polymorphisms (SNPs) in PD-1 gene in humans, it has been shown that there is a higher risk in relevant genetic associations with developing autoimmune diseases in certain ethnic groups. In this review we have tried to present a comprehensive role of PD-1:PD-L in all recently studied autoimmune diseases.

Disrupted regulatory T cell homeostasis in inflammatory bowel diseases

In the gut, where billions of non-self-antigens from the food and the microbiota are present, the immune response must be tightly regulated to ensure both host protection against pathogenic microorganisms and the absence of immune-related pathologies. It has been well documented that regulatory T cells (Tregs) play a pivotal role in this context. Indeed, Tregs are able to prevent excessive inflammation, which can lead to the rupture of intestinal homeostasis observed in inflammatory bowel diseases (IBDs). Both the worldwide incidence and prevalence of such diseases have increased throughout the latter part of the 20^th century. Therefore, it is crucial to understand how Tregs suppress the colitogenic immune cells to establish new treatments for patients suffering from IBDs. In this review, we will first summarize the results obtained in animal model studies that highlight the importance of Tregs in maintaining intestinal homeostasis and describe the specific suppressive mechanisms involved. Next, our current knowledge about Tregs contribution to human IBDs will be reviewed, as well as the current therapeutic perspective on using Tregs for clinical IBD treatment and the challenges that remain to be resolved to ensure both the safety and effectiveness of these therapies in targeting this critical immune-regulatory cell population.

Protective effects of Fc-fused PD-L1 on two different animal models of colitis

OBJECTIVE

Programmed death-ligand 1 (PD-L1) has been shown to negatively regulate immune responses via its interaction with PD-1 receptor. In this study, we investigated the effects of PD-L1-Fc treatment on intestinal inflammation using two murine models of inflammatory colitis induced by dextran sulfate sodium (DSS) and T-cell transfer.

DESIGN

The anti-colitis effect of adenovirus expressing Fc-conjugated PD-L1 (Ad/PD-L1-Fc) and recombinant PD-L1-Fc protein was evaluated in DSS-treated wild-type and Rag-1 knockout (KO) mice. We examined differentiation of T-helper cells, frequency of innate immune cells, and cytokine production by dendritic cells (DCs) in the colon from DSS-treated mice after PD-L1-Fc administration. In Rag-1 KO mice reconstituted with CD4 CD45RB(high) T cells, we assessed the treatment effect of PD-L1-Fc protein on the development of colitis.

RESULTS

Administration of Ad/PD-L1-Fc significantly ameliorated DSS-induced colitis, which was accompanied by diminished frequency of interleukin (IL)-17A-producing CD4 T cells and increased interferon-γ-producing CD4 T cells in the colon of DSS-fed mice. The anti-colitic effect of PD-L1-Fc treatment was also observed in DSS-treated Rag-1 KO mice, indicating lymphoid cell independency. PD-L1-Fc modulated cytokine production by colonic DCs and the effect was dependent on PD-1 expression. Furthermore, PD-L1-Fc protein could significantly reduce the severity of colitis in CD4 CD45RB(high) T-cell-transferred Rag-1 KO mice.

CONCLUSIONS

Based on the protective effect of PD-L1-Fc against DSS-induced and T-cell-induced colitis, our results suggest that PD-1-mediated inhibitory signals have a crucial role in limiting the development of colonic inflammation. This implicates that PD-L1-Fc may provide a novel therapeutic approach to treat inflammatory bowel disease.

Classical Th1 cells obtain colitogenicity by co-existence of RORγt-expressing T cells in experimental colitis

BACKGROUND

Both Th1 and Th17 cell types are involved in the pathogenesis of chronic intestinal inflammation. We recently demonstrated that retinoid-related orphan receptor gamma t (RORγt)-expressing Th17 cells are progenitor cells for alternative Th1 cells, which have the potential to induce colitis. However, the involvement of classical Th1 (cTh1) cells generated directly from naive T cells without RORγt expression in the pathogenesis of colitis remains poorly understood.

METHODS

We performed a series of in vivo experiments using a murine chronic colitis model induced by adoptive transfer of splenic CD4CD45RB(high) T cells obtained from wild-type, RORγt(gfp/gfp), or RORγt(gfp/gfp) mice into RAG-2(-/-) mice.

RESULTS

RAG-2(-/-) mice receiving transfer of in vitro-manipulated RORγt(gfp/gfp) Th1 cells developed colitis. RAG-2(-/-) mice co-transferred with splenic CD4CD45RB(high) T cells obtained from wild-type mice and RORγt(gfp/gfp) mice developed colitis with a significant increase in RORγt cTh1 cell numbers when compared with noncolitic mice transferred with splenic CD4CD45RB(high) T cells obtained from RORγt(gfp/gfp) mice. Furthermore, RAG-2(-/-) mice transferred with in vivo-manipulated RORγt(gfp/gfp) cTh1 cells developed colitis with a significant increase in RORγt(gfp/gfp) cTh1 cell numbers.

CONCLUSIONS

These findings indicate that both alternative Th1 cells and cTh1 cells have the potential to be colitogenic in an adaptive transfer model. The development of cTh1 cells was dependent on the co-existence of RORγt-expressing T cells, suggesting a critical role for the interactions of these cell types in the development of chronic intestinal inflammation.

A single strain of Clostridium butyricum induces intestinal IL-10-producing macrophages to suppress acute experimental colitis in mice

Imbalance in gut bacterial composition provokes host proinflammatory responses causing diseases such as colitis. Colonization with a mixture of Clostridium species from clusters IV and XIVa was shown to suppress colitis through the induction of IL-10-producing regulatory T (Treg) cells. We demonstrate that a distinct Clostridium strain from cluster I, Clostridium butyricum (CB), prevents acute experimental colitis in mice through induction of IL-10, an anti-inflammatory cytokine. However, while CB treatment had no effect on IL-10 production by T cells, IL-10-producing F4/80(+)CD11b(+)CD11c(int) macrophages accumulated in the inflamed mucosa after CB treatment. CB directly triggered IL-10 production by intestinal macrophages in inflamed mucosa via the TLR2/MyD88 pathway. The colitis-preventing effect of CB was negated in macrophage-specific IL-10-deficient mice, suggesting that induction of IL-10 by intestinal macrophages is crucial for the probiotic action of CB. Collectively, CB promotes IL-10 production by intestinal macrophages in inflamed mucosa, thereby preventing experimental colitis in mice.

Effects of the modulation of microbiota on the gastrointestinal immune system and bowel function

The gastrointestinal tract harbors a tremendous number and variety of commensal microbiota. The intestinal mucosa simultaneously absorbs essential nutrients and protects against detrimental antigens or pathogenic microbiota as the first line of defense. Beneficial interactions between the host and microbiota are key requirements for host health. Although the gut microbiota has been previously studied in the context of inflammatory diseases, it has recently become clear that this microbial environment has a beneficial role during normal homeostasis, by modulating the immune system or bowel motor function. Recent studies revealed that microbiota, including their metabolites, modulate key signaling pathways involved in the inflammation of the mucosa or the neurotransmitter system in the gut-brain axis. The underlying molecular mechanisms of host-microbiota interactions are still unclear; however, manipulation of microbiota by probiotics or prebiotics is becoming increasingly recognized as an important therapeutic option, especially for the treatment of the dysfunction or inflammation of the intestinal tract.

IL-7 promotes long-term in vitro survival of unique long-lived memory subset generated from mucosal effector memory CD4+ T cells in chronic colitis mice

Colitogenic memory CD4(+) T cells are important in the pathogenesis of inflammatory bowel disease (IBD). Although memory stem cells with high survival and self-renewal capacity were recently identified in both mice and humans, it is unclear whether a similar subset is present in chronic colitis mice. We sought to identify and purify a long-lived subset of colitogenic memory CD4(+) T cells, which may be targets for treatment of IBD. A long-lived subset of colitogenic memory CD4(+) T cells was purified using a long-term culture system. The characteristics of these cells were assessed. Interleukin (IL)-7 promoted the in vitro survival for >8 weeks of lamina propria (LP) CD4(+) T cells from colitic SCID mice previously injected with CD4(+)CD45RB(high) T cells. These cells were in a quiescent state and divided a maximum of 5 times in 4 weeks. LP CD4(+) T cells expressed higher levels of Bcl-2, integrin-α4β7, CXCR3 and CD25 after than before culture, as well as secreting high concentrations of IL-2 and low concentrations of IFN-γ and IL-17 in response to intestinal bacterial antigens. LP CD4(+) T cells from colitic mice cultured with IL-7 for 8 weeks induced more severe colitis than LP CD4(+) T cells cultured for 4 weeks. We developed a novel culture system to purify a long-lived, highly pathogenic memory subset from activated LP CD4(+) T cells. IL-7 promoted long-term in vitro survival of this subset in a quiescent state. This subset will be a novel, effective target for the treatment of IBD.

CD73 is a phenotypic marker of effector memory Th17 cells in inflammatory bowel disease

Purinergic signaling and associated ectonucleotidases, such as CD39 and CD73, have been implicated in the pathogenesis of inflammatory bowel disease (IBD). CD39 is known to be a Treg memory cell marker, and here we determine the phenotype and function of CD73(+) CD4(+) T lymphocytes in patients with IBD. We describe elevated levels of CD73(+) CD4(+) T cells in the peripheral blood and intestinal lamina propria of patients with active IBD. The functional phenotype of these CD73(+) CD4(+) T cells was further determined by gene expression, ecto-enzymatic activity, and suppressive assays. Increased numbers of CD73(+) CD4(+) T cells in the periphery and lamina propria were noted during active inflammation, which returned to baseline levels following anti-TNF treatment. Peripheral CD73(+) CD4(+) T cells predominantly expressed CD45RO, and were enriched with IL-17A(+) cells. The CD73(+) CD4(+) cell population expressed higher levels of RORC, IL-17A, and TNF, and lower levels of FOXP3 and/or CD25, than CD73(-) CD4(+) T cells. Expression of CD73 by peripheral CD4(+) T cells was increased by TNF, and decreased by an anti-TNF monoclonal antibody (infliximab). In vitro, these peripheral CD73(+) CD4(+) T cells did not suppress proliferation of CD25(-) effector cells, and expressed higher levels of pro-inflammatory markers. We conclude that the CD73(+) CD4(+) T-cell population in patients with active IBD are enriched with cells with a T-helper type 17 phenotype, and could be used to monitor disease activity during treatment.

Small intestine CD11c+ CD8+ T cells suppress CD4+ T cell-induced immune colitis

The large (LI) and small intestine (SI) differ in patterns of susceptibility to chronic mucosal inflammation. In this study, we evaluated whether this might, in part, reflect differences in resident mucosal CD11c(+) T cells. These cells comprised 39-48% (SI) and 12-17% (LI) of the intraepithelial compartment, most of which were T-cell receptor-αβ(+). In the SI, the majority of these cells were CD103(+) CD8(+) NK1.1(-), whereas the opposite phenotype prevailed in the LI. In transfer models of CD4(+) T cell-induced colitis, small numbers (2.5 × 10(5)) of SI CD11c(+) CD8(+) T cells suppressed proinflammatory cytokine-producing CD4(+) T cells in mesenteric lymph nodes and mucosa-associated lymphoid compartments (SI and LI) and protected mice from chronic inflammation. On a per-cell basis, the regulatory function of SI CD11c(+) T cells in CD4(+) T cell colitis was potent compared with other reported regulatory CD4(+) or CD8(+) T cells. In contrast, neither LI CD11c(+) T cells nor SI CD11c(-) T cells were effective in such immunoregulation. SI CD11c(+) CD8(+) T cells were similarly effective in suppressing CD4(+)CD45RB(hi) T cell colitis, as evidenced by inhibition of intracellular proinflammatory cytokine expression and histological inflammation. These findings indicate that SI CD11c(+) CD8(+) T cells are a distinct intestinal T cell population that plays an immunoregulatory role in control of proinflammatory CD4(+) T cells and maintenance of intestinal mucosal homeostasis.

New prebiotics from rice bran ameliorate inflammation in murine colitis models through the modulation of intestinal homeostasis and the mucosal immune system

BACKGROUND

Enzyme-treated rice fiber (ERF) is a recently developed prebiotic product made from rice bran by heat-resistant amylase, protease and hemicellulase treatment. Although the detailed mechanism of inflammatory bowel disease (IBD) is still unclear, the role of the resident luminal bacteria and its interaction on the mucosal barrier seem to be an important factor in the development of IBD and its chronicity. With the objective of manipulating the intestinal microbiota in IBD, this study was carried out to evaluate the effects of ERF on IBD with using experimental colitis models.

METHODS

Three colitis models were used and they were induced by the oral administration of dextran sodium sulfate in male Sprague-Dawley rats or BALB/c mice and transferring CD4+ CD45RB(high) T cells to female SCID mice, sequentially their CD4+ T cells were retransferred to new SCID mice. The evaluation included the measurement of body weight, spleen weight, colon length, histological examination, serum and mucosal cytokine (tumor necrosis factor-alpha (TNF-α), an interferon-gamma (IFN-γ), interleukin-12 p70 (IL-12p70), IL-1β, IL-6, IL-4) analysis, mucosal serotonin (5HT), and organic acid production and a microbiota analysis of the cecal contents. The characteristics of T cell surface markers including CD4, CD69, CD45RB of spleen and mesenteric lymph nodes (MLN) were also analyzed. In addition, the effects of ERF on the change in the induction of dendritic cells (DCs) were evaluated.

RESULTS

The preventive effect of ERF on colitis was significantly superior to that of raw material rice bran or control group. An overexpression of inflammatory cytokine production was attenuated by ERF treatment, which was accompanied with a decrease in both the colonic mucosal damage and 5HT production. Furthermore, ERF significantly attenuated the T cell activation (CD4+CD69+) of spleen and MLN, and this characteristic was inherited by the retransferred mice. ERF significantly suppressed the growth of Clostiridium, and increased short-chain fatty acids (acetate, propionate and butyrate) content in colitis. The relatively hydrophilic fraction of ERF (ethanol-methanol soluble fraction) is therefore considered to have a potent ability to attenuate the induction of DCs.

CONCLUSION

A new prebiotic, ERF, reduced inflammation by modulating the colonic environment and regulating immune cell differentiation. Although a more detailed study is required, this study showed the promising anti-inflammatory effects of an adjunctive prebiotic treatment for IBD.

IL-2 is positively involved in the development of colitogenic CD4+ IL-7R alpha high memory T cells in chronic colitis

IL-2 and IL-7 share a common gamma-chain receptor and are critical for T-cell homeostasis. We aimed to clarify the reciprocal roles of IL-2 and IL-7 in the development and persistence of chronic colitis. We performed a series of adoptive transfers of IL-2(-/-) CD4(+)CD45RB(high) T cells into RAG-2(-/-) mice and assessed the role of IL-2 in the induction of IL-7R alpha on colitogenic CD4(+) T cells and the development of chronic colitis. RAG-2(-/-) mice transferred with WT but not with IL-2(-/-) CD4(+)CD45RB(high) T cells developed Th1/Th17-mediated colitis. Consistently, re-expression of IL-7R alpha was severely impaired on IL-2(-/-) but not on WT CD4(+) T cells from the transferred mice. To exclude a contribution of the preclinical autoimmunity of IL-2(-/-)mice, WT Ly5.1(+) or IL-2(-/-) Ly5.2(+) CD4(+)CD45RB(high) T cells from GFP mice previously transplanted with the same number of WT and IL-2(-/-) BM cells were transferred into RAG-2(-/-) mice. RAG-2(-/-) mice transferred with IL-2(-/-)-derived CD4(+)CD45RB(high) T cells did not develop colitis, but their splenic CD4(+) T cells changed from effector-memory to central-memory type. These results show that IL-2 is critically involved in the establishment and maintenance of IL-7-dependent colitogenic memory CD4(+)IL-7R alpha(high) T cells.

Platelet-rich plasma may prevent titanium-mesh exposure in alveolar ridge augmentation with anorganic bovine bone

OBJECTIVE

Bone augmentation with the titanium-mesh (Ti-mesh) technique is susceptible to a large rate of complications such as morbidity of bone graft donor site, and mesh exposure to the oral cavity. The purpose of this study was to evaluate the effectiveness of anorganic bovine bone (ABB) in alveolar bone augmentation with the Ti-mesh technique. In addition, we investigated the effect of platelet-rich plasma (PRP) in preventing mesh exposure by using it to cover the Ti-mesh.

PATIENTS AND METHODS

Patients included in the clinical trial were randomly allocated by a blinded assistant into two groups. The 30 patients recruited for this study underwent 43 alveolar bone augmentation with the Ti-mesh technique using ABB as graft material in all of them. In 15 patients, the Ti-meshes were covered with PRP (PRP group) whereas in the other 15 the Ti-meshes were not (control group). After 6 months, patients were called for clinical, radiographic, and histological evaluation, and implant placement surgery. A total of 97 implants were placed in the augmented bone and their evolution was followed up for a period of 24 months.

RESULTS

Significant differences were found between the two study groups in terms of complications and bone formation. In the control group, 28.5% of the cases suffered from mesh exposure, while in the PRP group, no exposures were registered. Radiographic analysis revealed that bone augmentation was higher in the PRP group than in the control group. Overall, 97.3% of implants placed in the control group and 100% of those placed in the PRP group were successful during the monitoring period. We suggest that the positive effect of PRP on the Ti-mesh technique is due to its capacity to improve soft tissue healing, thereby protecting the mesh and graft material secured beneath the gingival tissues.

CONCLUSIONS

Alveolar bone augmentation using ABB alone in the Ti-mesh technique is sufficient for implant rehabilitation. Besides, covering the Ti-meshes with PRP was a determining factor in avoiding mesh exposure. Ti-mesh exposure provoked significant bone loss, but in most cases it did not affect the subsequent placement of implants.

The PD-1 pathway in tolerance and autoimmunity

Regulatory T cells (Tregs) and the PD-1: PD-ligand (PD-L) pathway are both critical to terminating immune responses. Elimination of either can result in the breakdown of tolerance and the development of autoimmunity. The PD-1: PD-L pathway can thwart self-reactive T cells and protect against autoimmunity in many ways. In this review, we highlight how PD-1 and its ligands defend against potentially pathogenic self-reactive effector T cells by simultaneously harnessing two mechanisms of peripheral tolerance: (i) the promotion of Treg development and function and (ii) the direct inhibition of potentially pathogenic self-reactive T cells that have escaped into the periphery. Treg cells induced by the PD-1 pathway may also assist in maintaining immune homeostasis, keeping the threshold for T-cell activation high enough to safeguard against autoimmunity. PD-L1 expression on non-hematopoietic cells as well as hematopoietic cells endows PD-L1 with the capacity to promote Treg development and enhance Treg function in lymphoid organs and tissues that are targets of autoimmune attack. At sites where transforming growth factor-beta is present (e.g. sites of immune privilege or inflammation), PD-L1 may promote the de novo generation of Tregs. When considering the consequences of uncontrolled immunity, it would be therapeutically advantageous to manipulate Treg development and sustain Treg function. Thus, this review also discusses how the PD-1 pathway regulates a number of autoimmune diseases and the therapeutic potential of PD-1: PD-L modulation.

Costimulation of Th17 cells: Adding fuel or putting out the fire in the inflamed gut?

Inflammatory bowel disease, typified by Crohn's disease and ulcerative colitis, is a common disorder characterized by recurrent and serious inflammation of the gastrointestinal tract. It is well documented that T cells play a pivotal role in the development of inflammatory bowel disease. Th17 cells are a unique T cell subpopulation implicated in inflammatory bowel disease and many other autoimmune/inflammatory diseases. However, the regulatory mechanism of Th17 activation and proliferation has not been defined completely. Recent studies have shown that the ligation of several costimulatory receptor-ligand pairs contributes to the activation, differentiation, and proliferation of T lymphocytes including the Th17 subset. In this review, we will discuss the emerging evidence on the role of Th17 cells in inflammatory bowel disease pathogenesis as well as the effect of costimulatory molecules on Th17 development and consider if the need for such costimulation of T lymphocytes provides a target for the development of novel therapeutic strategy.

Homeostatic (IL-7) and effector (IL-17) cytokines as distinct but complementary target for an optimal therapeutic strategy in inflammatory bowel disease

PURPOSE OF REVIEW

This review focuses on CD4+ T cells involved in the mediation of inflammatory tissue damage in murine models of inflammatory bowel diseases (IBDs). In particular, we describe the distinct roles of the homeostatic cytokine IL-7, which is essential to the maintenance of colitogenic memory CD4+ cells, and the newly discovered effector cytokine IL-17. We also discuss the close correlation between colitogenic Th17-type CD4+ T cells and inducible CD4+CD25+Foxp3+ regulatory T cells.

RECENT FINDINGS

IBDs are characterized by wasting and chronic intestinal inflammation induced by many different cytokine-mediated pathways. It is clearly recognized that medical and surgical interventions do not cure Crohn's disease because relapse is the rule after remission. Until a few years ago, IBD was classified into Th1-dependent, that is, Crohn's disease, and Th2-dependent, that is, ulcerative colitis, phenotypes. However, in recent years, it has been shown that new T-cell subclasses, that is, Th17 and regulatory T cells (T(R)), exist independently of Th1 and Th2 and that they play a central role in modulating IBD.

SUMMARY

The persistence of IL-7-dependent colitogenic memory CD4+ T cells is critical to the maintenance of experimental colitis. On the other hand, though Th1 and Th2 colitogenic memory CD4+ cells exist, in recent years the central role of IL-17-producing Th17-type cells in IBD has attracted renewed interest. The development of molecularly targeted therapies aimed at a variety of different Th-dependent pathogenic mechanisms may represent a novel approach to IBD therapy.