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Epigenetic regulation plays a key role in the link between inflammation and cancer. Here we examine Mbd2, which mediates epigenetic transcriptional silencing by binding to methylated DNA. In separate studies the Mbd2 −/− mouse has been shown (1) to be resistant to intestinal tumourigenesis and (2) to have an enhanced inflammatory/immune response, observations that are inconsistent with the links between inflammation and cancer. To clarify its role in tumourigenesis and inflammation, we used constitutive and conditional models of Mbd2 deletion to explore its epithelial and non‐epithelial roles in the intestine. Using a conditional model, we found that suppression of intestinal tumourigenesis is due primarily to the absence of Mbd2 within the epithelia. Next, we demonstrated, using the DSS colitis model, that non‐epithelial roles of Mbd2 are key in preventing the transition from acute to tumour‐promoting chronic inflammation. Combining models revealed that prior to inflammation the altered Mbd2 −/− immune response plays a role in intestinal tumour suppression. However, following inflammation the intestine converts from tumour suppressive to tumour promoting. To summarise, in the intestine the normal function of Mbd2 is exploited by cancer cells to enable tumourigenesis, while in the immune system it plays a key role in preventing tumour‐enabling inflammation. Which role is dominant depends on the inflammation status of the intestine. As environmental interactions within the intestine can alter DNA methylation patterns, we propose that Mbd2 plays a key role in determining whether these interactions are anti‐ or pro‐tumourigenic and this makes it a useful new epigenetic model for inflammation‐associated carcinogenesis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

BackgroundMacrophages are pivotal in coordinating a range of important processes in the intestines, including controlling intracellular infections and limiting damaging inflammation against the microbiota. However, it is unclear how gut macrophages, relative to recruited blood monocytes and other myeloid cells contribute to the intestinal inflammatory milieu nor how macrophages and their monocyte precursors mediate recruitment of other immune cells to the inflamed intestine.Methods Myeloid cell populations isolated from colonic IBD or murine dextran sulphate sodium (DSS) induced colitis were assessed using flow cytometry and compared to healthy controls. In addition, mRNA expression profiles in human and murine colon samples, and in macrophages and monocytes from healthy and inflamed murine colons, were analysed by quantitative PCR (qPCR) and mRNA microarray. ResultsWe show that the macrophage:monocyte balance is disrupted in colon inflammation to favour recruitment of CD14+HLA-DRInt cells in humans, and Ly6CHi monocytes in mice. In addition, we identify that murine blood monocytes receive systemic signals enabling increased release of IL-1β prior to egress from the blood into the colon. Further, once within the colon and relative to other myeloid cells, monocytes represent the dominant local sources of both IL-1β and TNF. Finally, our data reveal that, independent of inflammation, murine colon macrophages act as major sources of Ccl7 and Ccl8 mRNA, chemokines that trigger further recruitment of their pro-inflammatory monocyte precursors. ConclusionsOur work suggests that strategies targeting macrophage-mediated monocyte recruitment may represent a promising approach for limiting the chronic inflammation that characterises IBD.

Retinoic acid modulates the functions of IL-4 in alternatively activated DCs, The archetypal Th2 cytokine IL-4 has previously been shown to alternatively activate murine macrophages and, more recently, dendritic cells (DCs) both in vitro and in vivo. IL-4 has also been shown to induce Aldh1a2 (aldehyde dehydrogenase 1a2) expression in murine macrophages recruited to the peritoneal cavity. However, the influence of IL-4 on DC Aldh1a2 induction in vivo has not yet been addressed. In this work, we found that DCs show enhanced aldehyde dehydrogenase enzyme activity in vivo, which led us to investigate the impact of the vitamin A metabolite all-trans retinoic acid (RA) on DC alternative activation and function. Antagonism of RA receptors reduced production of resistin-like molecule alpha by DCs responding to IL-4, while addition of exogenous RA enhanced production of this marker of alternative activation. Functionally, RA increased DC induction of CD4+ T-cell IL-10, while reducing CD4+ T-cell IL-4 and IL-13, revealing a previously unidentified role for RA in regulating the ability of alternatively activated DCs to influence Th2 polarization.

Dendritic cells (DCs) direct CD4+ T-cell differentiation into diverse helper (Th) subsets that are required for protection against varied infections. However, the mechanisms used by DCs to promote Th2 responses, which are important both for immunity to helminth infection and in allergic disease, are currently poorly understood. We demonstrate a key role for the protein methyl-CpG-binding domain-2 (Mbd2), which links DNA methylation to repressive chromatin structure, in regulating expression of a range of genes that are associated with optimal DC activation and function. In the absence of Mbd2, DCs display reduced phenotypic activation and a markedly impaired capacity to initiate Th2 immunity against helminths or allergens. These data identify an epigenetic mechanism that is central to the activation of CD4+ T-cell responses by DCs, particularly in Th2 settings, and reveal methyl-CpG-binding proteins and the genes under their control as possible therapeutic targets for type-2 inflammation., How anti-helminth and allergic immune responses are initiated is poorly understood. Here the authors show that to trigger these responses, dendritic cells specifically require methyl-CpG-binding domain-2, a protein promoting repressed chromatin state.

The effect that multiple percutaneous exposures to Schistosoma larvae has on the development of early CD4+ lymphocyte reactivity is unclear, yet it is important in the context of humans living in areas where schistosomiasis is endemic. In a murine model of multiple infections, we show that exposure of mice to repeated doses (4×) of Schistosoma mansoni cercariae, compared to a single dose (1×), results in CD4+ T cell hyporesponsiveness within the skin-draining lymph nodes (sdLN), manifested as reduced CD4+ cell proliferation and cytokine production. FoxP3+ CD4+ regulatory T cells were present in similar numbers in the sdLN of 4× and 1× mice and thus are unlikely to have a role in effecting hyporesponsiveness. Moreover, anergy of the CD4+ cell population from 4× mice was slight, as proliferation was only partly circumvented through the in vitro addition of exogenous interleukin-2 (IL-2), and the in vivo blockade of the regulatory molecule PD1 had a minimal effect on restoring responsiveness. In contrast, IL-10 was observed to be critical in mediating hyporesponsiveness, as CD4+ cells from the sdLN of 4× mice deficient for IL-10 were readily able to proliferate, unlike those from 4× wild-type cohorts. CD4+ cells from the sdLN of 4× mice exhibited higher levels of apoptosis and cell death, but in the absence of IL-10, there was significantly less cell death. Combined, our data show that IL-10 is a key factor in the development of CD4+ T cell hyporesponsiveness after repeated parasite exposure involving CD4+ cell apoptosis.

Th1 and Th2 cell fates are traditionally viewed as mutually exclusive, but recent work suggests that these lineages may be more plastic than previously thought. When isolating splenic CD4(+) T cells from mice infected with the parasitic helminth Schistosoma mansoni, we observed a defined population of IFN-γ/IL-4 double-positive cells. These IFN-γ(+) IL-4(+) cells showed differences in DNA methylation at the Ifng and Il4 loci when compared with IFN-γ(+) IL-4(-) (Th1) and IFN-γ(-) IL-4(+) (Th2) cells, demonstrating that they represent a distinct effector cell population. IFN-γ(+) IL-4(+) cells also displayed a discrete DNA methylation pattern at a CpG island within the body of the Gata3 gene, which encodes the master regulator of Th2 identity. DNA methylation at this region correlated with decreased Gata3 levels, suggesting a possible role in controlling Gata3 expression. These data provide important insight into the molecular mechanisms behind the co-existence of Th1 and Th2 characteristics.