Continuous generation of colitogenic CD4+ T cells in persistent colitis

Th9 cells and IL-9 in autoimmune disorders: Pathogenesis and therapeutic potentials

Naïve CD4⁺ T cells are pleiotropically divided into various T helper (Th) cell subsets, according to their pivotal roles in the regulation of immune responses. The differentiation of Th9 cells, an interleukin (IL)-9 producing subset, can be impacted by specific environmental cues, co-stimulation with transforming growth factor β (TGF-β) and IL-4, and other regulatory factors. Although IL-9 has been recognized as a classical Th2-related cytokine, recent studies have indicated that IL-9-producing cells contribute to a group of autoimmune disorders including systemic lupus erythematosus (SLE), multiple sclerosis (MS), inflammatory bowel diseases (IBD), rheumatoid arthritis (RA) and psoriasis. Studies of Th9 cells in autoimmune diseases, although in their infancy, are expected to be of growing interest in the study of potential mechanisms of cytokine regulatory pathways and autoimmune pathogenesis. Several in vitro and in vivo pre-clinical trials have been conducted to explore potential therapeutic strategies by targeting the IL-9 pathway. Specifically, anti-IL-9 monoclonal antibodies (mAbs) and IL-9 inhibitors may potentially be used for the clinical treatment of allergic diseases, autoimmune diseases or cancers. Here, we review recent research on Th9 cells and IL-9 pertaining to cell differentiation, biological characteristics and pivotal cellular inter-relationships implicated in the development of various diseases.

Tetrahydrobiopterin Attenuates DSS-evoked Colitis in Mice by Rebalancing Redox and Lipid Signalling

BACKGROUND AND AIMS

Guanosine triphosphate cyclohydrolase [GCH1] governs the production of the enzyme cofactor tetrahydrobiopterin [BH4] which is essential for biogenic amine synthesis, lipid metabolism via alkylglycerol monooxygenase [AGMO], and redox coupling of nitric oxide synthases [NOSs]. Inflammation-evoked unequal regulation of GCH1 and NOS or AGMO may cause redox stress and lipid imbalances.

METHODS

The present study assessed potential therapeutic effects of rebalancing these systems with BH4 in experimental colitis in mice.

RESULTS

Oral treatment with BH4 as a suspension of crushed tablets attenuated colitis, whereas inhibition of its production had opposite effects: aggravated weight loss, epithelial haemorrhages and ulcers, neutrophil infiltrates, production of reactive oxygen species, and unfavourable profile changes of endocannabinoids, ceramides, and lysophosphatidic acids. Conversely, oral BH4 normalised biopterin, reduced in vivo activity of oxidases and peroxidases in the inflamed gut, favoured nitric oxide over hydrogen peroxide, and maintained normal levels of lipid signalling molecules. BH4 favoured thereby resident CD3+CD8+ and regulatory CD3+CD25+ intraepithelial T cells that are important for epithelial integrity.

CONCLUSIONS

BH4 protected against colitis in mice via two major pathways: [i] by reduction of oxidative stress; and [ii] by re-orchestration of alkyl- and acylglycerolipid signalling via AGMO. Oral treatment with BH4 is a safe approved supplementary therapy for genetic BH4 deficiency and did not excessively increase systemic BH4 levels. Therefore, one may consider repurposing of oral BH4 as an adjunctive treatment for colitis.

Harnessing regulatory T cells for the treatment of inflammatory bowel disease

Regulatory CD4 T (Treg) cells are comprised of a heterogeneous population of cells that play a vital role in suppressing inflammation and maintaining immune tolerance. The immunoregulatory function of Treg cells is especially important in the intestine where the mucosa is exposed to a diverse array of foreign antigens-including those derived from food and commensal bacteria. Treg cells are enriched in the intestinal lamina propria and provide a crucial function in promoting tolerance to enteric antigens while modulating tissue inflammation. Correspondingly, Treg cell dysfunction is associated with a breakdown in intestinal tolerance and the induction of aberrant immune responses that may contribute to the pathogenesis of inflammatory bowel disease. This review will provide a brief overview of Treg cell biology with a focus on Foxp3 Treg and type 1 regulatory (Tr1) cells and summarize the evidence for defective Treg cells in experimental and human inflammatory bowel disease. The potential application of Treg cells as a treatment for inflammatory bowel disease will also be discussed in the context of Treg infusion therapy and the in vivo induction/expansion of intestinal Treg cells.

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.

Late Crohn's disease patients present an increase in peripheral Th17 cells and cytokine production compared with early patients

BACKGROUND

Th1 and Th17 cells have been implicated in Crohn's disease (CD) pathophysiology and may play a role in disease persistence. Aim To determine Th1 and Th17 responses in intestine and peripheral blood of early (<32 weeks since initial symptoms) and late (>2 years) CD patients.

METHODS

Cytokine mRNA in intestinal biopsies was determined by RT-PCR. Cytokine concentration in culture was measured by ELISA and cytokine-producing cells were identified by intracellular staining.

RESULTS

The inflamed mucosa showed significantly increased IL-17 mRNA levels compared with non-inflamed areas, both in early and late CD patients. However, only patients with late (n = 12), but not early (n = 9), active disease showed increased IL-17 production, as well as a significantly higher percentage of IL-17(+)CD4(+) cells in blood, compared with controls (n = 12) or patients in remission (n = 13). Moreover, cultured peripheral CD4(+) cells from late active CD patients presented significantly higher percentages of IL-17(+), IL-22(+) and IFN-gamma(+) and a significantly increased production of IL-17 and IL-22, but not IFN-gamma(+).

CONCLUSIONS

Increased IL-17 gene transcription is common to early and late CD mucosa. However, exacerbated Th17 responses in the peripheral blood appear only in late disease. We propose that this population may constitute a mechanism of perpetuating the disease.