Early and Sustained Improvements in Symptoms and Quality of Life with Upadacitinib in Adults and Adolescents with Moderate-to-Severe Atopic Dermatitis: 52-Week Results from Two Phase III Randomized Clinical Trials (Measure Up 1 and Measure Up 2)

BACKGROUND

Atopic dermatitis is a chronic inflammatory disease characterized by increased itch, skin pain, poor sleep quality, and other symptoms that negatively affect patient quality of life. Upadacitinib, an oral selective Janus kinase (JAK) inhibitor with greater inhibitory potency for JAK1 than JAK2, JAK3, or tyrosine kinase 2, is approved to treat moderate-to-severe atopic dermatitis.

OBJECTIVE

We aimed to evaluate the effect of upadacitinib on patient-reported outcomes over 52 weeks in adults and adolescents with moderate-to-severe atopic dermatitis.

METHODS

Data from two phase III monotherapy trials of upadacitinib (Measure Up 1, NCT03569293; Measure Up 2, NCT03607422) were integrated. Changes in pruritus, pain, other skin symptoms, sleep, quality of life, mental health, and patient impression were evaluated. Patient-reported outcome assessments included the Worst Pruritus Numerical Rating Scale, Patient-Oriented Eczema Measure, Dermatology Life Quality Index, Atopic Dermatitis Symptom Scale, Atopic Dermatitis Impact Scale, Hospital Anxiety and Depression Scale, SCORing Atopic Dermatitis index, Patient Global Impression of Severity, Patient Global Impression of Change, and Patient Global Impression of Treatment. Minimal clinically important differences, achievement of scores representing minimal disease burden, and the change from baseline were evaluated in patients who received upadacitinib through week 52 and in patients who received placebo through week 16.

RESULTS

This analysis included 1609 patients (upadacitinib 15 mg, N = 557; upadacitinib 30 mg, N = 567; placebo, N = 485). Baseline demographics and disease characteristics were generally similar across all arms. The proportion of patients treated with upadacitinib reporting improvements in itch increased rapidly by week 1, increased steadily through week 8, and was sustained through week 52. Patients receiving upadacitinib also experienced improvements in pain and other skin symptoms by week 1, which continued through week 16; improvements were maintained through week 52. Patient reports of improved sleep increased rapidly from baseline to week 1, increased steadily through week 32, and were sustained through week 52. Patients experienced quality-of-life improvements through week 8, which were maintained through week 52. By week 1, patients in both upadacitinib groups experienced rapid improvements in emotional state, and by week 12, patients also achieved meaningful improvements in anxiety and depression. Improvements in mental health continued steadily through week 32 and were maintained through week 52. Patients treated with upadacitinib 30 mg generally experienced improvements in patient-reported outcomes earlier than those treated with upadacitinib 15 mg. Through week 16, patients receiving upadacitinib experienced greater improvements versus those receiving placebo in all assessed patient-reported outcomes.

CONCLUSIONS

Adults and adolescents with moderate-to-severe atopic dermatitis treated with once-daily upadacitinib 15 or 30 mg experienced early improvements in itch, pain, other skin symptoms, sleep, quality of life, and mental health that were sustained through week 52.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifiers NCT03569293 (13 August 2018) and NCT03607422 (27 July 2018).

Aggregate Response Benefit in Skin Clearance and Itch Reduction With Upadacitinib or Dupilumab in Patients With Moderate-to-Severe Atopic Dermatitis

Background: In patients with moderate-to-severe atopic dermatitis (AD), greater skin clearance and itch reduction are associated with more pronounced improvements in quality of life (QoL). Objective: To characterize the aggregate response benefit with upadacitinib versus dupilumab or placebo in patients with moderate-to-severe AD. Methods: Degree of skin clearance and itch response in 3 phase 3 studies (Heads Up [NCT03738397] and Measure Up 1/2 [integrated; NCT03569293/NCT03607422]) were assessed by the Eczema Area and Severity Index (EASI) and Worst Pruritus Numerical Rating Scale (WP-NRS), respectively, using mutually exclusive categories. The aggregate response benefit with upadacitinib over dupilumab or placebo was determined by summing incremental differences for each EASI or WP-NRS category across the full distribution of patient responses. Results: Comparisons across EASI improvement threshold distributions, EASI severity levels, and WP-NRS categories demonstrated an aggregate response benefit favoring upadacitinib over dupilumab as early as week 4 and continuing at weeks 16 and 24. Similar trends were observed for upadacitinib 15 and 30 mg versus placebo. Conclusions: The aggregate response benefit in skin clearance and itch reduction favored upadacitinib 30 mg over dupilumab and upadacitinib 15 or 30 mg over placebo. These benefits may translate to overall greater improvements in patient QoL.

The role of Janus kinase signaling in the pathology of atopic dermatitis

Atopic dermatitis (AD) is a heterogeneous, chronic, relapsing, inflammatory skin disease associated with considerable physical, psychological, and economic burden. The pathology of AD includes complex interactions involving abnormalities in immune and skin barrier genes, skin barrier disruption, immune dysregulation, microbiome disturbance, and other environmental factors. Many of the cytokines involved in AD pathology, including IL-4, IL-13, IL-22, IL-31, thymic stromal lymphopoietin, and IFN-γ, signal through the Janus kinase (JAK)-signal transducer and activation of transcription (STAT) pathway. The JAK family includes JAK1, JAK2, JAK3, and tyrosine kinase 2; the STAT family includes STAT1, STAT2, STAT3, STAT4, STAT5A/B, and STAT6. Activation of the JAK-STAT pathway has been implicated in the pathology of several immune-mediated inflammatory diseases, including AD. However, the exact mechanisms of JAK-STAT involvement in AD have not been fully characterized. This review aims to discuss current knowledge about the role of the JAK-STAT signaling pathway and, specifically, the role of JAK1 in the pathology and symptomology of AD.

Efficacy and Safety of Upadacitinib Treatment in Adolescents With Moderate-to-Severe Atopic Dermatitis: Analysis of the Measure Up 1, Measure Up 2, and AD Up Randomized Clinical Trials

Importance

Atopic dermatitis onset usually occurs in childhood. Persistence of disease into adolescence and adulthood is common. It is important to evaluate new treatment options in adolescents because of the high unmet need in this population.

Objective

To assess the efficacy and safety of upadacitinib to treat moderate-to-severe atopic dermatitis in adolescents.

Design, Setting, and Participants

Prespecified analysis of adolescents enrolled in 3 randomized, double-blind, placebo-controlled phase 3 clinical trials in more than 20 countries across Europe, North and South America, Oceania, the Middle East, and the Asia-Pacific region from July 2018 through December 2020. Participants were adolescents aged 12 to 17 years with moderate-to-severe atopic dermatitis. Data analysis was performed from April to August 2021.

Interventions

Patients were randomized (1:1:1) to once-daily oral upadacitinib 15 mg, upadacitinib 30 mg, or placebo alone (Measure Up 1 and Measure Up 2) or with topical corticosteroids (AD Up).

Main Outcomes and Measures

Safety and efficacy, including at least a 75% improvement in the Eczema Area and Severity Index from baseline and validated Investigator Global Assessment for Atopic Dermatitis score of 0 (clear) or 1 (almost clear) at week 16 (coprimary end points).

Results

A total of 552 adolescents (290 female; 262 male) were randomized. Mean (SD) age was 15.4 (1.8), 15.5 (1.7), and 15.3 (1.8) years for adolescents in Measure Up 1, Measure Up 2, and AD Up, respectively. In Measure Up 1, Measure Up 2, and AD Up, respectively, a greater proportion of adolescents (% [95% CI]) achieved at least 75% improvement in the Eczema Area and Severity Index at week 16 with upadacitinib 15 mg (73% [63%-84%], 69% [57%-81%], 63% [51%-76%]), and upadacitinib 30 mg (78% [68%-88%], 73% [62%-85%], 84% [75%-94%]), than with placebo (12% [4%-20%], 13% [5%-22%], 30% [19%-42%]; nominal P < .001 for all comparisons vs placebo). Similarly, a greater proportion of adolescents treated with upadacitinib achieved a validated Investigator Global Assessment for Atopic Dermatitis score of 0 or 1 at week 16 and improvements in quality of life with upadacitinib than with placebo. Upadacitinib was generally well tolerated in adolescents. Acne was the most common adverse event, and all acne events were mild or moderate.

Conclusions and Relevance

In this analysis of 3 randomized clinical trials, upadacitinib was an effective treatment for adolescents with moderate-to-severe atopic dermatitis, with an acceptable safety profile.

Trial Registration

ClinicalTrials.gov Identifiers: NCT03569293 (Measure Up 1), NCT03607422 (Measure Up 2), and NCT03568318 (AD Up).

Macrophages Subvert Adaptive Immunity to Urinary Tract Infection

Urinary tract infection (UTI) is one of the most common bacterial infections with frequent recurrence being a major medical challenge. Development of effective therapies has been impeded by the lack of knowledge of events leading to adaptive immunity. Here, we establish conclusive evidence that an adaptive immune response is generated during UTI, yet this response does not establish sterilizing immunity. To investigate the underlying deficiency, we delineated the naïve bladder immune cell compartment, identifying resident macrophages as the most populous immune cell. To evaluate their impact on the establishment of adaptive immune responses following infection, we measured bacterial clearance in mice depleted of either circulating monocytes, which give rise to macrophages, or bladder resident macrophages. Surprisingly, mice depleted of resident macrophages, prior to primary infection, exhibited a nearly 2-log reduction in bacterial burden following secondary challenge compared to untreated animals. This increased bacterial clearance, in the context of a challenge infection, was dependent on lymphocytes. Macrophages were the predominant antigen presenting cell to acquire bacteria post-infection and in their absence, bacterial uptake by dendritic cells was increased almost 2-fold. These data suggest that bacterial uptake by tissue macrophages impedes development of adaptive immune responses during UTI, revealing a novel target for enhancing host responses to bacterial infection of the bladder.

Urinary tract infection is a common infection with a high propensity for recurrence. The majority of infections are caused by uropathogenic E. coli, a growing public health concern with increasing prevalence of antibiotic resistant strains. Finding therapeutic options that circumvent the need for antibiotics, while boosting patients’ immune response to infection is desirable to counteract further increases in antibiotic resistance and to provide long-lasting resistance to infection. Currently, little is known about how adaptive immune responses, which typically prevent recurrent infection in other organs, arise from the bladder during urinary tract infection. Here, we investigated the initial interactions between immune cell populations of the bladder and uropathogenic E. coli, finding that macrophages are the principal cell population to engulf bacteria. Interestingly, these same cells appear to inhibit the development of adaptive immunity to the bacteria, as their depletion, prior to primary infection, results in a stronger immune response during bacterial challenge. We found that in the absence of macrophages, dendritic cells, which are the most potent initiators of adaptive immunity, are able to take up more bacteria for presentation. Our study has revealed a mechanism in which specific immune cells may act in a manner detrimental to host immunity.

Collecting lymphatic vessel permeability facilitates adipose tissue inflammation and distribution of antigen to lymph node-homing adipose tissue dendritic cells

Collecting lymphatic vessels (CLVs), surrounded by fat and endowed with contractile muscle and valves, transport lymph from tissues after it is absorbed into lymphatic capillaries. CLVs are not known to participate in immune responses. In this study, we observed that the inherent permeability of CLVs allowed broad distribution of lymph components within surrounding fat for uptake by adjacent macrophages and dendritic cells (DCs) that actively interacted with CLVs. Endocytosis of lymph-derived Ags by these cells supported recall T cell responses in the fat and also generated Ag-bearing DCs for emigration into adjacent lymph nodes (LNs). Enhanced recruitment of DCs to inflammation-reactive LNs significantly relied on adipose tissue DCs to maintain sufficient numbers of Ag-bearing DCs as the LN expanded. Thus, CLVs coordinate inflammation and immunity within adipose depots and foster the generation of an unexpected pool of APCs for Ag transport into the adjacent LN.

Normal dendritic cell mobilization to lymph nodes under conditions of severe lymphatic hypoplasia

To address the requirement for lymphatic capillaries in dendritic cell (DC) mobilization from skin to lymph nodes (LNs), we used mice bearing one inactivated allele of vascular endothelial growth factor receptor 3 (VEGFR3) where skin lymphatic capillaries are reported absent. Unexpectedly, DC mobilization from the back skin to draining LNs was similar in magnitude, and kinetics to control mice and humoral immunity appeared intact. By contrast, DC migration from body extremities, including ear and forepaws, was ablated. An evaluation in different regions of skin revealed rare patches of lymphatic capillaries only in body trunk areas where migration was intact. That is, whereas the ear skin was totally devoid of lymphatic capillaries, residual capillaries in the back skin were present though retained only at ∼10% normal density. This reduction in density markedly reduced the clearance of soluble tracers, indicating that normal cell migration was spared under conditions when lymphatic transport function was poor. Residual lymphatic capillaries expressed slightly higher levels of CCL21 and migration of skin DCs to LNs remained dependent on CCR7 in Chy mice. DC migration from the ear could be rescued by the introduction of a limited number of lymphatic capillaries through skin transplantation. Thus, the development of lymphatic capillaries in the skin of body extremities was more severely impacted by a mutant copy of VEGFR3 than trunk skin, but lymphatic transport function was markedly reduced throughout the skin, demonstrating that even under conditions when a marked loss in lymphatic capillary density reduces lymph transport, DC migration from skin to LNs remains normal.

Lymphatic vasculature mediates macrophage reverse cholesterol transport in mice

Reverse cholesterol transport (RCT) refers to the mobilization of cholesterol on HDL particles (HDL-C) from extravascular tissues to plasma, ultimately for fecal excretion. Little is known about how HDL-C leaves peripheral tissues to reach plasma. We first used 2 models of disrupted lymphatic drainage from skin--1 surgical and the other genetic--to quantitatively track RCT following injection of [3H]-cholesterol-loaded macrophages upstream of blocked or absent lymphatic vessels. Macrophage RCT was markedly impaired in both models, even at sites with a leaky vasculature. Inhibited RCT was downstream of cholesterol efflux from macrophages, since macrophage efflux of a fluorescent cholesterol analog (BODIPY-cholesterol) was not altered by impaired lymphatic drainage. We next addressed whether RCT was mediated by lymphatic vessels from the aortic wall by loading the aortae of donor atherosclerotic Apoe-deficient mice with [2H]6-labeled cholesterol and surgically transplanting these aortae into recipient Apoe-deficient mice that were treated with anti-VEGFR3 antibody to block lymphatic regrowth or with control antibody to allow such regrowth. [2H]-Cholesterol was retained in aortae of anti-VEGFR3-treated mice. Thus, the lymphatic vessel route is critical for RCT from multiple tissues, including the aortic wall. These results suggest that supporting lymphatic transport function may facilitate cholesterol clearance in therapies aimed at reversing atherosclerosis.

Dendritic cell migration through the lymphatic vasculature to lymph nodes

The mobilization of antigen-presenting dendritic cells (DCs) from peripheral tissues to draining lymph nodes drives the initiation of adaptive immune responses. Recent advances have been made in understanding how and where DCs enter the lymphatic vasculature and what mechanisms control this process. In this chapter, we highlight these advances. Delineating DC-lymphatic vessel interactions is critical for our fundamental understanding of DC trafficking in states of health and disease and for efforts to manipulate DC mobilization for immunotherapy and vaccination.

Plasmacytoid dendritic cells: biomarkers or potential therapeutic targets in atherosclerosis?

Plasmacytoid dendritic cells (pDCs) represent a unique subset of dendritic cells that play distinct and critical roles in the immune response. Importantly, pDCs play a pivotal role in several chronic autoimmune diseases strongly characterized by an increased risk of vascular pathology. Clinical studies have shown that pDCs are detectable in atherosclerotic plaques and others have suggested an association between reduced numbers of circulating pDCs and cardiovascular events. Although the causal relationship between pDCs and atherosclerosis is still uncertain, recent results from mouse models are starting to define the specific role(s) of pDCs in the disease process. In this review, we will discuss the role of pDCs in innate and adaptive immunity, the emerging evidence demonstrating the contribution of pDCs to vascular pathology and we will consider the possible impact of pDCs on the acceleration of atherosclerosis in chronic inflammatory autoimmune diseases. Finally, we will discuss how pDCs could be targeted for therapeutic utility.

Abstract 17: Reverse Cholesterol Transport Relies on a Functional Lymphatic Network

Introduction: HDL accepts free cholesterol from cells within extravascular tissues and transports it to the liver for excretion. Little is known about how HDL-C leaves such tissues to reach the blood. HDL-C is found in lymph, but it is unclear if lymphatics are critical for mobilization of HDL-C from tissues.

Methods & Results: We employed models of disrupted lymphatic drainage--one a surgical resection of lymphatics in the mouse tail and the other a genetic lack of skin lymphatics due to a mutation in VEGFR3--to quantify the role of lymphatic vessels in movement of HDL-C out of skin to plasma. We implanted bone marrow macrophages loaded with [ 3 H]-cholesterol in skin sites and then quantified [ 3 H]-cholesterol in plasma, liver, and feces. [ 3 H]-cholesterol movement into plasma was reduced by 80% in both models of disrupted lymphatics, and this result was unaffected by conditions of a leaky blood vessels. To ensure that this reduction reflected events between efflux and appearance of cholesterol in plasma rather than altered macrophage cholesterol efflux, we substituted [ 3 H]-cholesterol-loaded macrophages with congenic macrophages loaded with a fluorescently modified cholesterol compound that allowed us to monitor ABCA1/ABCG1-dependent efflux from individual macrophages in the same assays and models. Flow cytometric analysis of bodipy-cholesterol-loaded macrophages retrieved from injection sites revealed similar efflux in mice lacking functional lymphatics as in controls.

Conclusions: Mobilization of HDL-C from extravascular tissues to plasma occurs through the lymphatic vasculature. Recent studies show that transport through lymphatic vessels is compromised by hypercholesterolemia. Hypercholesterolemia-induced impairments in lymphatic function may retard clearance of cholesterol from extravascular tissues, possibly including atherosclerotic plaques.

Abatacept modulates proinflammatory macrophage responses upon cytokine-activated T cell and Toll-like receptor ligand stimulation

OBJECTIVES

We investigated whether Abatacept might reduce proinflammatory cytokine production by macrophages upon contact with cytokine activated T cells and/or stimulation with TLR ligands.

METHODS

Macrophages and cytokine stimulated T cells (Tck) were added together in the presence of Abatacept or a control Ig, with or without TLR ligands. The production of cytokines was determined by luminex.

RESULTS

Abatacept reduced Tck-induced production of TNFa by macrophages. Tck and TLR ligands synergistically induced the production of proinflammatory cytokines by macrophages, especially IL-12p70. The production of IL-12p70 coincided with the production of IFNg, which were both reduced in the presence of Abatacept.

CONCLUSIONS

Tck induce the production of TNFa by macrophages and facilitate the highly increased production of proinflammatory cytokines in the presence of TLR ligands. Abatacept was shown to potently suppress these pathways suggesting that its role may extend beyond antigen specific T cell mediated effector function.

Monocyte trafficking in acute and chronic inflammation

Environmental signals at the site of inflammation mediate rapid monocyte mobilization and dictate differentiation programs whereby these cells give rise to macrophages or dendritic cells. Monocytes participate in tissue healing, clearance of pathogens and dead cells, and initiation of adaptive immunity. However, recruited monocytes can also contribute to the pathogenesis of infection and chronic inflammatory disease, such as atherosclerosis. Here, we explore monocyte trafficking in the context of acute inflammation, relying predominantly on data from microbial infection models. These mechanisms will be compared to monocyte trafficking during chronic inflammation in experimental models of atherosclerosis. Recent developments suggest that monocyte trafficking shares common themes in diverse inflammatory diseases; however, important differences exist between monocyte migratory pathways in acute and chronic inflammation.

Abatacept limits breach of self-tolerance in a murine model of arthritis via effects on the generation of T follicular helper cells

Abatacept modulates CD28-mediated T cell costimulation and is efficacious in the treatment of rheumatoid arthritis (RA). Its mechanism of action has not been fully elucidated but will likely reveal critical pathologic pathways in RA. We show that abatacept substantially modulated Ag-specific T and B cell responses in vivo. Ag-specific T cell proliferation was reduced, and the acquisition of an activated phenotype, characterized by upregulation of CD69, OX40, ICOS, and programmed death-1 and downregulation of CD62L, was suppressed. Furthermore, abatacept suppressed the production of inflammatory cytokines, such as IFN-gamma and IL-17. These effects were associated with a failure of Ag-specific T cells to acquire the CXCR5(+)ICOS(+) T follicular helper cell phenotype. This, in turn, led to a failure of these cells to enter B cell follicles, resulting in reduced specific Ab responses, despite normal B cell clonal expansion. To test the pathologic significance of this, we used a novel model of RA associated with breach of self-tolerance to self-Ag and demonstrated that abatacept prevented the emergence of self-reactivity. Thus, CD28-dependent signaling is required for optimal T follicular helper cell maturation and expansion, and its inhibition prevents loss of self-tolerance in a model of articular pathology. Thus, we provide a novel mode of action for abatacept with profound implications for its potential usefulness in early inflammatory arthropathies associated with autoantibody expression.

An independent subset of TLR expressing CCR2-dependent macrophages promotes colonic inflammation

Macrophages (Mphis) in the large intestine are crucial effectors of inflammatory bowel disease, but are also essential for homeostasis. It is unclear if these reflect separate populations of Ms or if resident Ms change during inflammation. In this study, we identify two subsets of colonic Ms in mice, whose proportions differ in healthy and inflamed intestine. Under resting conditions, most F4/80+ Ms are TLR- CCR2- CX3CR1hi and do not produce TNF-alpha in response to stimulation. The lack of TLR expression is stable, affects all TLRs, and is determined both transcriptionally and posttranscriptionally. During experimental colitis, TLR2+ CCR2+ CX3CR1int Ly6Chi Gr-1+, TNF-alpha-producing Ms come to dominate, and some of these are also present in the normal colon. The TLR2+ and TLR2- subsets are phenotypically distinct and have different turnover kinetics in vivo, and these properties are not influenced by the presence of inflammation. There is preferential CCR2-dependent recruitment of the proinflammatory population during colitis, suggesting they are derived from independent myeloid precursors. CCR2 knockout mice show reduced susceptibility to colitis and lack the recruitment of TLR2+ CCR2+ Gr-1+, TNF-alpha-producing Ms. The balance between proinflammatory and resident Ms in the colon is controlled by CCR2-dependent recruitment mechanisms, which could prove useful as targets for therapy in inflammatory bowel disease.

IL-10-dependent partial refractoriness to Toll-like receptor stimulation modulates gut mucosal dendritic cell function

The default response of the intestinal immune system to most antigens is the induction of immunological tolerance, which is difficult to reconcile with the constant exposure to ligands for TLR and other pattern recognition receptors. We showed previously that dendritic cells (DC) from the lamina propria of normal mouse intestine may be inherently tolerogenic and here we have explored how this might relate to the expression and function of Toll-like receptors (TLR). Lamina propria (LP) DC showed higher levels of TLR 2, 3, 4 and 9 protein expression than spleen and MLN DC, with most TLR-expressing DC in the gut being CD11c(lo), class II MHC(lo), CD103(-), CD11b(-) and F4/80(-). TLR expression by lamina propria DC was low in the upper small intestine and higher in distal small intestine and colon. Freshly isolated lamina propria DC expressed some CD40, CD80, CD86 and functional CCR7. These were up-regulated on CD11c(lo), but not on CD11c(hi) LP DC by stimulation via TLR. However, there was little induction of IL-12 by either subset in response to TLR ligation. This was associated with constitutive IL-10 production and was reversed by blocking IL-10 function. Thus, IL-10 may maintain LP DC in a partially unresponsive state to TLR ligation, allowing them to have a critical role in immune homeostasis in the gut.

Mucosal macrophages and the regulation of immune responses in the intestine

The healthy intestinal mucosa is home to one of the largest populations of macrophages (mvarphi) in the body [Lee SH, Starkey PM, Gordon S. Quantitative analysis of total macrophage content in adult mouse tissues. Immunochemical studies with monoclonal antibody F4/80. J Exp Med 1985;161:475-89], yet little is known about their function. Resident mvarphi in the large and small intestine are distinct from other mvarphi populations in the body, with regards to both their functional properties and surface phenotype. They respond in an unconventional manner to inflammatory stimuli, with little upregulation of proteins involved in antigen presentation and T cell co-stimulation, and no production of pro-inflammatory cytokines. This suggests that under resting conditions, intestinal mvarphi may be conditioned to be anti-inflammatory in response to local stimuli such as commensal bacteria. In contrast, during inflammation, intestinal mvarphi exhibit increased bactericidal and inflammatory abilities, promote protective immunity and/or mediate pathology. Thus the status of this cell may be the key to understanding how the intestine maintains a balance between being able to generate protective immunity against pathogens, but still prevent pathological inflammation under normal conditions. In this review, we discuss the current knowledge of intestinal mvarphi biology, and highlight the different levels of immunoregulation which influence these cells, with particular focus on innate pathogen recognition receptor (PRR) function and responsiveness to microbial stimuli.