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To understand the contribution of mononuclear phagocytes (MNP), which include monocyte-derived intestinal macrophages, to the pathogenesis of inflammatory bowel disease (IBD), it is necessary to identify functionally-different MNP populations. We aimed to characterise intestinal macrophage populations in patients with IBD. We developed 12-parameter flow cytometry protocols to identify and human intestinal MNPs. We used these protocols to purify and characterize colonic macrophages from colonic tissue from patients with Crohn’s disease (CD), ulcerative colitis (UC), or non-inflamed controls, in a cross-sectional study. We identify macrophage populations (CD45 + CD64 + HLA-DR + ) and describe two distinct subsets, differentiated by their expression of the mannose receptor, CD206. CD206 + macrophages expressed markers consistent with a mature phenotype: high levels of CD68 and CD163, higher transcription of IL-10 and lower expression of TREM1. CD206 − macrophages appear to be less mature, with features more similar to their monocytic precursors. We identified and purified macrophage populations from human colon. These appear to be derived from a monocytic precursor with high CCR2 and low CD206 expression. As these cells mature, they acquire expression of IL-10, CD206, CD63, and CD168. Targeting the newly recruited monocyte-derived cells may represent a fruitful avenue to ameliorate chronic inflammation in IBD.

Type 2 immunity is activated in response to both allergens and helminth infection. It can be detrimental or beneficial, and there is a pressing need to better understand its regulation. The immunosuppressive cytokine IL-10 is known as a T helper 2 (Th2) effector molecule, but it is currently unclear whether IL-10 dampens or promotes Th2 differentiation during infection. Here we show that helminth infection in mice elicits IL-10 expression in both the intestinal lamina propria and the draining mesenteric lymph node, with higher expression in the infected tissue. In vitro, exogenous IL-10 enhanced Th2 differentiation in isolated CD4+ T cells, increasing expression of GATA3 and production of IL-5 and IL-13. The ability of IL-10 to amplify the Th2 response coincided with its suppression of IFNγ expression and in vivo we found that, in intestinal helminth infection, IL-10 receptor expression was higher on Th1 cells in the small intestine than on Th2 cells in the same tissue, or on any Th cell in the draining lymph node. In vivo blockade of IL-10 signalling during helminth infection resulted in an expansion of IFNγ+ and Tbet+ Th1 cells in the small intestine and a coincident decrease in IL-13, IL-5 and GATA3 expression by intestinal T cells. These changes in Th2 cytokines correlated with reduced expression of type 2 effector molecules, such as RELMα, and increased parasite egg production. Together our data indicate that IL-10 signalling promotes Th2 differentiation during helminth infection at least in part by regulating competing Th1 cells in the infected tissue.

T-helper 2 (Th2) cell responses defend against parasites. Although dendritic cells (DCs) are vital for the induction of T-cell responses, the DC subpopulations that induce Th2 cells in the intestine are unidentified. Here we show that intestinal Th2 responses against Trichuris muris worms and Schistosoma mansoni eggs do not develop in mice with IRF-4-deficient DCs (IRF-4 f/f CD11c-cre). Adoptive transfer of conventional DCs, in particular CD11b-expressing DCs from the intestine, is sufficient to prime S. mansoni -specific Th2 responses. Surprisingly, transferred IRF-4-deficient DCs also effectively prime S. mansoni -specific Th2 responses. Egg antigens do not induce the expression of IRF-4-related genes. Instead, IRF-4 f/f CD11c-cre mice have fewer CD11b + migrating DCs and fewer DCs carrying parasite antigens to the lymph nodes. Furthermore, CD11b + CD103 + DCs induce Th2 responses in the small intestine, whereas CD11b + CD103 − DCs perform this role in the colon, revealing a specific functional heterogeneity among intestinal DCs in inducing Th2 responses. T helper 2 (Th2) cell responses are essential for immunity against parasites, but how Th2 response is modulated in the gut is still unclear. Here the authors show that distinct dendritic cell subsets distinguishable by CD11b, CD103 and IRF4 function in the small intestine or colon to promote Th2 responses.

FoxP3+ regulatory T cells (Tregs) control inflammation and maintain mucosal homeostasis, but their functions during infection are poorly understood. Th1, Th2, and Th17 cells can be identified by master transcription factors (TFs) T-bet, GATA3, and RORγT; Tregs also express these TFs. While T-bet+ Tregs can selectively suppress Th1 cells, it is unclear whether distinct Treg populations can alter Th bias. To address this, we used Salmonella enterica serotype Typhimurium to induce nonlethal colitis. Following infection, we observed an early colonic Th17 response within total CD4 T cells, followed by a Th1 bias. The early Th17 response, which contains both Salmonella-specific and non-Salmonella-specific cells, parallels an increase in T-bet+ Tregs. Later, Th1 cells and RORγT+ Tregs dominate. This reciprocal dynamic may indicate that Tregs selectively suppress Th cells, shaping the immune response. Treg depletion 1–2 days post-infection shifted the early Th17 response to a Th1 bias; however, Treg depletion 6–7 days post-infection abrogated the Th1 bias. Thus, Tregs are necessary for the early Th17 response, and for a maximal Th1 response later. These data show that Tregs shape the overall tissue CD4 T cell response and highlight the potential for subpopulations of Tregs to be used in targeted therapeutic approaches.

The balance of type 1 and type 2 immune responses plays a crucial role in anti-helminth immunity and can either support chronic infection or drive type 2 mediated expulsion of the parasite. Helminth antigens and secreted molecules directly influence this balance and induce a favorable immunological environment for the parasite's survival. However, less is known if the site of infection also influences the balance of type 1 and type 2 immunity. Here, we report that tissue-specific immune responses are mounted against helminth antigens, which elicited strong IL-4 responses when injected into the skin, while the same antigen, delivered into the intestinal subserosa, induced increased IFN- and reduced Th2 responses. Immune responses in individual mesenteric lymph nodes that drain defined regions of the intestine furthermore displayed a site-specific pattern of type 1 and type 2 immunity after or infection. egg-specific Th2 responses were detectable in all mesenteric lymph nodes but Th1 responses were only present in those draining the colon, while infection elicited mixed Th1 and Th2 responses in the lymph nodes associated with the site of infection. Similar site-specific type 1 and type 2 immune responses were observed in the draining lymph nodes after the controlled delivery of eggs into different segments of the small and large intestine using microsurgical techniques. Different subsets of intestinal dendritic cells were hereby responsible for the uptake and priming of Th1 and Th2 responses against helminth antigens. Migratory CD11b CD103 and especially CD11b CD103 DC2s transported egg antigens to the draining lymph nodes to induce Th1 and Th2 responses, while CD103 DC1s induced only IFN- responses. In contrast, antigens were predominantly transported by CD11b CD103 DC2s and CD103 DC1s and all DC subsets induced similar Th1 but weaker Th2 responses, compared to egg antigens. The development of adaptive anti-helminth immune responses is therefore influenced by the antigen itself, the uptake and priming characteristics of antigen-positive dendritic cell subsets and the site of infection, which shape the level of Th1 and Th2 responses in order to create a favorable immunological environment for the parasite.

While immune responses have been rigorously examined after intravenous ( ) infection, less is understood about its dissemination from the intestines or the induction of adaptive immunity after more physiologic models of foodborne infection. Consequently, this study focused on early events in the intestinal mucosa and draining mesenteric lymph nodes (MLN) using foodborne infection of mice with modified to invade murine intestinal epithelium (InlA . InlA trafficked intracellularly from the intestines to the MLN and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this, InlA initially disseminated from the gut to the MLN normally in mice. Activated migratory DC accumulated in the MLN by 3 days post-infection and surrounded foci of InlA . At this time mice displayed reduced InlA burdens, implicating cDC1 in maximal bacterial accumulation in the MLN. mice also exhibited profound defects in the induction and gut-homing of InlA -specific effector CD8 T cells. Restoration of pathogen burden did not rescue antigen-specific CD8 T cell responses in mice, indicating a critical role for in generating anti-InlA immunity following foodborne infection. Collectively, these data suggest that DC play diverse, dynamic roles in the early events following foodborne InlA infection and in driving the establishment of intestinal -specific effector T cells.

Conventional dendritic cells (cDCs) are important antigen presenting cells which link innate and adaptive immunity by transferring antigenic information from peripheral organs to T cells in lymph nodes (LNs). However, despite their central function in the induction of adaptive immune responses, the kinetics and molecular regulation of the cDC life cycle and migration remain poorly understood. Using a variety of in vivo techniques, we examine the kinetics of cDC turnover in the intestine and address the molecular changes throughout the various stages of the cDC life cycle – from tissue entry and differentiation to CCR7 upregulation and subsequent migration into draining LNs. Our data demonstrate that the life cycle of gut cDCs is highly dynamic, characterised by continuous alterations in transcriptome, protein expression and proliferation rates. These progressive changes culminate in cDC homeostatic activation and migration resulting in a resource-intensive daily turnover of up to a quarter of intestinal cDCs and an almost complete daily replacement of the migratory cDC compartment in the mesenteric LN. This high turnover rate ensures that the mesenteric LN maintains an accurate reflection of the intestinal immunological state, supporting rapid adaptation to emerging immune challenges. Conventional Dendritic cells (cDCs) continually migrate from peripheral tissues in homeostasis. Here, the authors analyse the homeostatic turnover of cDC subsets in the intestine from tissue entry to migration to the draining lymph nodes, noting a dynamic life cycle with changes in transcriptome and proliferation rates.

Current treatments for rheumatoid arthritis (RA) do not reverse underlying aberrant immune function. A genetic predisposition to RA, such as HLA-DR4 positivity, indicates that dendritic cells (DC) are of crucial importance to pathogenesis by activating auto-reactive lymphocytes. Here we show that microRNA-34a provides homoeostatic control of CD1c + DC activation via regulation of tyrosine kinase receptor AXL, an important inhibitory DC auto-regulator. This pathway is aberrant in CD1c + DCs from patients with RA, with upregulation of miR-34a and lower levels of AXL compared to DC from healthy donors. Production of pro-inflammatory cytokines is reduced by ex vivo gene-silencing of miR-34a. miR-34a-deficient mice are resistant to collagen-induced arthritis and interaction of DCs and T cells from these mice are reduced and do not support the development of Th17 cells in vivo . Our findings therefore show that miR-34a is an epigenetic regulator of DC function that may contribute to RA. Axl is a TAM receptor that can inhibit Toll-like receptor (TLR) -induced pro-inflammatory production by dendritic cells (DC). Here the authors show that miR-34a targets Axl to control CD1c+ DC activity in mice, and that miR-34a-deficient mice are resistant to collagen-induced arthritis, whereas DCs from patients with rheumatoid arthritis have high levels of miR- 34a.

The experiments presented here are based on the reconfiguration of an ancient medicine, Lemnian Earth (LE) ( terra sigillata , stamped earth , sphragis ), an acclaimed therapeutic clay with a 2500-year history of use. Based on our hypothesis that LE was not a natural material but an artificially modified one involving a clay-fungus interaction, we present results from experiments involving the co-culture of a common fungus, Penicillium purpurogenum ( Pp ), with two separate clay slurries, smectite and kaolin, which are the principal constituents of LE. Our results show: (a) the leachate of the Pp +smectite co-culture is antibacterial in vitro , inhibiting the growth of both Gram-positive and Gram-negative bacteria; (b) in vivo , supplementation of regular mouse diet with leachates of Pp +smectite increases intestinal microbial diversity; (c) Pp+ kaolin does not produce similar results; (d) untargeted metabolomics and analysis of bacterial functional pathways indicates that the Pp +smectite-induced microbiome amplifies production of short-chain fatty acids (SCFAs) and amino acid biosynthesis, known to modulate intestinal and systemic inflammation. Our results suggest that the combination of increased microbial diversity and SCFA production indicates beneficial effects on the host microbiome, thus lending support to the argument that the therapeutic properties of LE may have been based on the potential for modulating the gut microbiome. Our experiments involving reconfigured LE open the door to future research into small molecule-based sources for promoting gut health.

Adherent invasive Escherichia coli (AIEC) have been implicated as a causative agent of Crohn's disease (CD) due to their isolation from the intestines of CD sufferers and their ability to persist in macrophages inducing granulomas. The rapid intracellular multiplication of AIEC sets it apart from other enteric pathogens such as Salmonella Typhimurium which after limited replication induce programmed cell death (PCD). Understanding the response of infected cells to the increased AIEC bacterial load and associated metabolic stress may offer insights into AIEC pathogenesis and its association with CD. Here we show that AIEC persistence within macrophages and dendritic cells is facilitated by increased proteasomal degradation of caspase-3. In addition S-nitrosylation of pro- and active forms of caspase-3, which can inhibit the enzymes activity, is increased in AIEC infected macrophages. This S-nitrosylated caspase-3 was seen to accumulate upon inhibition of the proteasome indicating an additional role for S-nitrosylation in inducing caspase-3 degradation in a manner independent of ubiquitination. In addition to the autophagic genetic defects that are linked to CD, this delay in apoptosis mediated in AIEC infected cells through increased degradation of caspase-3, may be an essential factor in its prolonged persistence in CD patients.