Homing marker expression on circulating dendritic cells correlates with different phenotypes of Crohn's disease

Effects of Golimumab and Ustekinumab on Circulating Dendritic Cell Migratory Capacity in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic condition which includes ulcerative colitis (UC) and Crohn's disease (CD), the origins of which are not yet fully understood. Both conditions involve an exacerbated immune response in the intestinal tract, leading to tissue inflammation. Dendritic cells (DCs) are antigen-presenting cells crucial for maintaining tolerance in the gastrointestinal mucosa. Previous research has indicated that DC recruitment to the intestinal mucosa is more pronounced in individuals with IBD, but the specific mechanisms governing this migration remain unclear. This study aimed to assess the expression of various homing markers and the migratory abilities of circulating DC subsets in response to intestinal chemotactic signals. Additionally, this study examined how golimumab and ustekinumab impact these characteristics in individuals with IBD compared to healthy controls. The findings revealed that a particular subset of DCs known as type 2 conventional DCs (cDC2) displayed a more pronounced migratory profile compared to other DC subsets. Furthermore, the study observed that golimumab and ustekinumab had varying effects on the migratory profile of cDC1 in individuals with CD and UC. While CCL2 did not exert a chemoattractant effect on DC subsets in this patient cohort, treatment with golimumab and ustekinumab enhanced their migratory capacity towards CCL2 and CCL25 while reducing their migration towards MadCam1. In conclusion, this study highlights that cDC2 exhibits a heightened migratory profile towards the gastrointestinal mucosa compared to other DC subsets. This finding could be explored further for the development of new diagnostic biomarkers or the identification of potential immunomodulatory targets in the context of IBD.

Differential Effects of Anti-TNFα and Anti-α4β7 Drugs on Circulating Dendritic Cells Migratory Capacity in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is an idiopathic and chronic disorder that includes ulcerative colitis (UC) and Crohn’s disease (CD). Both diseases show an uncontrolled intestinal immune response that generates tissue inflammation. Dendritic cells (DCs) are antigen-presenting cells that play a key role in tolerance maintenance in the gastrointestinal mucosa. Although it has been reported that DC recruitment by the intestinal mucosa is more prominent in IBD patients, the specific mechanisms governing this migration are currently unknown. In this study, the expression of several homing markers and the migratory profile of circulating DC subsets towards intestinal chemo-attractants were evaluated and the effect of biological drugs with different mechanisms of action, such as anti-TNFα or anti-integrin α4β7 (vedolizumab), on this mechanism in healthy controls (HCs) and IBD patients was also assessed. Our results revealed that type 2 conventional DCs (cDC2) express differential homing marker profiles in UC and CD patients compared to HCs. Indeed, integrin β7 was differentially modulated by vedolizumab in CD and UC. Additionally, although CCL2 displayed a chemo-attractant effect over cDC2, while biological therapies did not modulate the expression of the homing markers, we paradoxically found that anti-TNF-treated cDC2 increased their migratory capacity towards CCL2 in HCs and IBD. Our results therefore suggest a key role for cDC2 migration towards the intestinal mucosa in IBD, something that could be explored in order to develop novel diagnostic biomarkers or to unravel new immunomodulatory targets in IBD.

Profiling of Human Circulating Dendritic Cells and Monocyte Subsets Discriminates Between Type and Mucosal Status in Patients With Inflammatory Bowel Disease

BACKGROUND

Intestinal dendritic cells (DC) and macrophages drive disease progression in patients with inflammatory bowel disease (IBD). We aimed to characterize the activation and homing profile of human circulating DC and monocyte subsets in healthy control patients (CP) and IBD patients.

METHODS

Eighteen CP and 64 patients with IBD were categorized by diagnoses of Crohn disease (CD) and ulcerative colitis (UC), either endoscopically active (inflamed) or quiescent. Circulating type 1 conventional DC, type 2 conventional DC, plasmacytoid DC, classical monocytes, nonclassical monocytes, and intermediate monocytes were identified by flow cytometry in each individual and characterized for the expression of 18 markers. Association between DC/monocytes and IBD risk was tested by logistic regression. Discriminant canonical analyses were performed to classify the patients in their own endoscopy category considering all markers on each subset.

RESULTS

CCRL1, CCR3, and CCR5 expression on circulating type 1 DC; CCRL1 expression on nonclassical monocytes; and CCR9 and β7 expression on classical monocytes allowed us to discriminate among the different study groups. Indeed, the same markers (excluding β7) were also associated with IBD when all DC and monocyte subsets were considered at the same time.

CONCLUSIONS

Monitoring the phenotype of human circulating DC and monocyte subsets may provide novel tools as biomarkers for disease diagnosis (CD/UC) or mucosal status (inflamed/noninflamed) in the absence of an invasive colonoscopy.

The Role of Inflammation in Crohn's Disease Recurrence after Surgical Treatment

Introduction

Postoperative recurrence after surgery for Crohn's disease (CD) is virtually inevitable, and its mechanism is poorly known.

Aim

To review the numerous factors involved in CD postoperative recurrence (POR) pathogenesis, focusing on single immune system components as well as the immune system as a whole and highlighting the clinical significance in terms of preventive strategies and future perspectives.

Methods

A systematic literature search on CD POR, followed by a review of the main findings.

Results

The immune system plays a pivotal role in CD POR, with many different factors involved. Memory T-lymphocytes retained in mesenteric lymph nodes seem to represent the main driving force. New pathophysiology-based preventive strategies in the medical and surgical fields may help reduce POR rates. In particular, surgical strategies have already been developed and are currently under investigation.

Conclusions

POR is a complex phenomenon, whose driving mechanisms are gradually being unraveled. New preventive strategies addressing these mechanisms seem promising.

Intestinal Dendritic Cells in Health and Gut Inflammation

Dendritic cells (DCs) mediate tolerance to food antigens, limit reactivity to the gut microbiota and are required for optimal response to intestinal pathogens. Intestinal DCs are heterogeneous but collectively generate both regulatory and effector T cell responses. The balance of outcomes is determined by the activity of functionally distinct DC subsets and their modulation by environmental cues. DCs constantly sample luminal content to monitor for pathogens; the significance of the various pathways by which this occurs is incompletely understood. Intestinal DC have distinctive properties shaped by local host, dietary and microbial signals. These properties include the ability to produce all-trans retinoic acid (RA) and imprint gut tropism on T cells they activate. In the steady-state, subsets of intestinal DC are potent generators of inducible Treg, aided by their ability to activate TGFβ and produce RA. However, responses induced by steady-state intestinal DCs are not exclusively regulatory in nature; effector T cells with specificity for commensal bacterial can be found in the healthy mucosa and these can be locally controlled to prevent inflammation. The ability of intestinal DCs to enhance effector responses in infection or sustain inflammation in disease is likely to involve both modulation of the local DC population and recruitment of additional populations. Immune pathways in the pathogenesis of inflammatory bowel disease can be mapped to DCs and in inflamed intestinal tissue, DCs show increased expression of microbial recognition machinery, activation, and production of key immunological mediators. Intestinal DCs may be targeted for disease therapy or to improve vaccine responses.

Human Intestinal Dendritic Cells in Inflammatory Bowel Diseases

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a serious, costly, and persistent health problem with an estimated prevalence in Western countries around 0.5% of the general population; its socioeconomic impact is comparable with that for chronic diseases such as diabetes. Conventional treatment involves escalating drug regimens with concomitant side effects followed, in some cases, by surgical interventions, which are often multiple, mainly in Crohn's disease. The goal of finding a targeted gut-specific immunotherapy for IBD patients is therefore an important unmet need. However, to achieve this goal we first must understand how dendritic cells (DC), the most potent antigen present cells of the immune system, control the immune tolerance in the gastrointestinal tract and how their properties are altered in those patients suffering from IBD. In this review, we summarize the current available information regarding human intestinal DC subsets composition, phenotype, and function in the human gastrointestinal tract describing how, in the IBD mucosa, DC display pro-inflammatory properties, which drive disease progression. A better understanding of the mechanisms inducing DC abnormal profile in IBD may provide us with novel tools to perform tissue specific immunomodulation.

Dendritic Cell-T-Cell Circuitry in Health and Changes in Inflammatory Bowel Disease and Its Treatment

BACKGROUND

Dendritic, antigen-presenting cells (DCs) determine not only whether lymphocytes produce different types of immune response but also tissue-homing profiles of lymphocytes they stimulate. For example, in health, mucosal DC stimulate T cells focused to home to the mucosa; DC/T-cell circuitry thus targets immune responses to specific tissue locations. Therapies being introduced for inflammatory bowel disease (IBD) include antibodies to gut-homing molecules such as α4β7 (Vedolizumab) used ostensibly to block gut-homing lymphocytes. However, such lymphocytes are dependent on the tissue specificity of DC that stimulated them.

KEY MESSAGES

In health, blood DCs have the potential to home to multiple tissues including gut (α4β7+) and skin (CLA+). DCs have become gut-specific within the intestinal microenvironment stimulated partially by local retinoid to express α4β7 (mucosal homing marker) and/or CCR9 (ileal homing marker) in the absence of skin-specific indicators. They spread veiled extensions, sample their environment, acquire/process antigens, produce cytokines and initiate innate immunity. Myeloid DC also traffic to draining lymph nodes where compartmentalization of adaptive immune responses is determined by DCs from the site of antigen exposure which dictate the homing profiles of lymphocytes they stimulate. In IBD, site and activity of disease are reflected in changes in homing/activation of gut DCs and T-cells they stimulate and also, in greater gut specificity and activation of blood DC. Homing potential of DC can be modulated toward mucosa or skin by vitamins A and D, respectively. Infliximab or interleukin-6 can divert homing profiles toward skin, perhaps predisposing to skin involvement in IBD. Probiotic bacteria or their products can also change homing profiles of gut DC toward skin homing and away from gut.

CONCLUSIONS

In conclusion, development of gut focused inflammation and its treatment relies on changes in DC tissue specificity; therefore, removal or diversion of gut-homing DC as well as T-cells is likely to be critical in prevention of gut-focused inflammation in IBD.