Resident Intestinal Macrophages Research Articles

The relationship between extreme inter-individual variation in macrophage gene expression and genetic susceptibility to inflammatory bowel disease

The differentiation of resident intestinal macrophages from blood monocytes depends upon signals from the macrophage colony-stimulating factor receptor (CSF1R). Analysis of genome-wide association studies (GWAS) indicates that dysregulation of macrophage differentiation and response to microorganisms contributes to susceptibility to chronic inflammatory bowel disease (IBD). Here, we analyzed transcriptomic variation in monocyte-derived macrophages (MDM) from affected and unaffected sib pairs/trios from 22 IBD families and 6 healthy controls. Transcriptional network analysis of the data revealed no overall or inter-sib distinction between affected and unaffected individuals in basal gene expression or the temporal response to lipopolysaccharide (LPS). However, the basal or LPS-inducible expression of individual genes varied independently by as much as 100-fold between subjects. Extreme independent variation in the expression of pairs of HLA-associated transcripts (HLA-B/C, HLA-A/F and HLA-DRB1/DRB5) in macrophages was associated with HLA genotype. Correlation analysis indicated the downstream impacts of variation in the immediate early response to LPS. For example, variation in early expression of IL1B was significantly associated with local SNV genotype and with subsequent peak expression of target genes including IL23A, CXCL1, CXCL3, CXCL8 and NLRP3. Similarly, variation in early IFNB1 expression was correlated with subsequent expression of IFN target genes. Our results support the view that gene-specific dysregulation in macrophage adaptation to the intestinal milieu is associated with genetic susceptibility to IBD.

Muscularis macrophages controlled by NLRP3 maintain the homeostasis of excitatory neurons.

Peristaltic movements in gut are essential to propel ingested materials through the gastrointestinal tract. Intestinal resident macrophages play an important role in this physiological function through protecting enteric neurons. However, it is incompletely clear how individuals maintain the homeostasis of gut motility. Here we found that NLRP3 is a critical factor in controlling loss of muscularis resident macrophages (MMs), and demonstrate that MMs are involved in the homeostasis of excitatory neurons such as choline acetyltransferase (ChAT)+ and vesicular glutamate transporter 2 (VGLUT2)+ but not inhibitory neuronal nitric oxide synthase (nNOS)+ neurons. NLRP3 knockout (KO) mice had enhanced gut motility and increased neurons, especially excitatory ChAT+ and VGLUT2+ neurons. Single cell analyses showed that there had increased resident macrophages, especially MMs in NLRP3 KO mice. The MM proportion in the resident macrophages was markedly higher than those in wild-type (WT) or caspase 1/11 KO mice. Deletion of the MMs and transplantation of the NLRP3 KO bone marrow cells showed that survival of the gut excitatory ChAT+ and VGLUT2+ neurons was dependent on the MMs. Gut microbiota metabolites β-hydroxybutyrate (BHB) could promote gut motility through protecting MMs from pyroptosis. Thus, our data suggest that MMs regulated by NLRP3 maintain the homeostasis of excitatory neurons.

Macrophage regulation of the "second brain": CD163 intestinal macrophages interact with inhibitory interneurons to regulate colonic motility - evidence from the Cx3cr1-Dtr rat model.

Intestinal macrophages are well-studied for their conventional roles in the immune response against pathogens and protecting the gut from chronic inflammation. However, these macrophages may also have additional functional roles in gastrointestinal motility under typical conditions. This is likely to occur via both direct and indirect influences on gastrointestinal motility through interaction with myenteric neurons that contribute to the gut-brain axis, but this mechanism is yet to be properly characterised. The CX3CR1 chemokine receptor is expressed in the majority of intestinal macrophages, so we used a conditional knockout Cx3cr1-Dtr (diphtheria toxin receptor) rat model to transiently ablate these cells. We then utilized ex vivo video imaging to evaluate colonic motility. Our previous studies in brain suggested that Cx3cr1-expressing cells repopulate by 7 days after depletion in this model, so we performed our experiments at both the 48 hr (macrophage depletion) and 7-day (macrophage repopulation) time points. We also investigated whether inhibitory neuronal input driven by nitric oxide from the enteric nervous system is required for the regulation of colonic motility by intestinal macrophages. Our results demonstrated that CD163-positive resident intestinal macrophages are important in regulating colonic motility in the absence of this major inhibitory neuronal input. In addition, we show that intestinal macrophages are indispensable in maintaining a healthy intestinal structure. Our study provides a novel understanding of the interplay between the enteric nervous system and intestinal macrophages in colonic motility. We highlight intestinal macrophages as a potential therapeutic target for gastrointestinal motility disorders when inhibitory neuronal input is suppressed.

The Loss of YTHDC1 in Gut Macrophages Exacerbates Inflammatory Bowel Disease.

The nuclear N6 -methyladenosine (m6 A) reader YT521-B homology-domain-containing protein 1 (YTHDC1) is required to maintain embryonic stem cell identity. However, little is known about its biological functions in intestinal-resident macrophages and inflammatory bowel disease (IBD). Herein, it is demonstrated that macrophage-specific depletion or insufficiency of YTHDC1 accelerates IBD development in animal models. On the molecular basis, YTHDC1 reduction in IBD-derived macrophages is attributed to Zinc finger protein 36 (ZFP36)-induced mRNA degradation. Importantly, transcriptome profiling and mechanistic assays unveil that YTHDC1 in macrophages regulates Ras homolog family member H (RHOH) to suppress inflammatory responses and fine-tunes NME nucleoside diphosphate kinase 1 (NME1) to enhance the integrity of colonic epithelial barrier, respectively. Collectively, this study identifies YTHDC1 as an important factor for the resolution of inflammatory responses and restoration of colonic epithelial barrier in the setting of IBD.

Development of Human Gut Organoids With Resident Tissue Macrophages as a Model of Intestinal Immune Responses.

Development of Human Gut Organoids With Resident Tissue Macrophages as a Model of Intestinal Immune Responses.

Macrophage as a Peripheral Pain Regulator.

A neuroimmune crosstalk is involved in somatic and visceral pathological pain including inflammatory and neuropathic components. Apart from microglia essential for spinal and supraspinal pain processing, the interaction of bone marrow-derived infiltrating macrophages and/or tissue-resident macrophages with the primary afferent neurons regulates pain signals in the peripheral tissue. Recent studies have uncovered previously unknown characteristics of tissue-resident macrophages, such as their origins and association with regulation of pain signals. Peripheral nerve macrophages and intestinal resident macrophages, in addition to adult monocyte-derived infiltrating macrophages, secrete a variety of mediators, such as tumor necrosis factor-α, interleukin (IL)-1β, IL-6, high mobility group box 1 and bone morphogenic protein 2 (BMP2), that regulate the excitability of the primary afferents. Neuron-derived mediators including neuropeptides, ATP and macrophage-colony stimulating factor regulate the activity or polarization of diverse macrophages. Thus, macrophages have multitasks in homeostatic conditions and participate in somatic and visceral pathological pain by interacting with neurons.

Physiologic expression of AhR regulates CX3CR1+ resident intestinal macrophages and promotes diabetes in NOD mice

Abstract Susceptibility to type 1 diabetes (T1D) is influenced by both genetic and environmental factors. The environmental sensor, the aryl hydrocarbon receptor (AhR), is expressed in mucosal immune cells and can be activated by metabolites derived from the diet and microbiome. We hypothesized that these metabolites may influence the autoimmune response and subsequent susceptibility to T1D. To test this hypothesis, we generated NOD AhR knockout mice and examined the intestinal immune response and development of T1D. Female AhR knockout mice had reduced insulitis at 12 weeks of age, and a decreased incidence and onset of hyperglycemia in comparison to their wild type littermates. To determine whether physiologic expression of AhR was altering the immune response, we analyzed CD4+ T cell subsets and identified an increase in IL-10R+Foxp3+ Tregs in the lamina propria (LP) of AhR knockout mice. We also discovered a population of resident-like macrophages (CD11b+CX3CR1+) in the small intestine LP that were negatively regulated by AhR. These cells have a very strong positive correlation to LP Tregs, and correlate with protection against insulitis in NOD mice. To identify the potential source of AhR ligands that regulate these resident-like macrophages, mice were fed an AhR ligand-deficient diet. These cells were not further regulated by dietary ligands, suggesting that AhR activation originates from the intestinal microbiome. Current studies are aimed at determining how AhR regulates the expression of LP resident-like macrophages and how these cells impose their immunoregulatory functions during T1D pathogenesis.

Intestinal Macrophages Balance Inflammatory Expression Profiles via Vitamin A and Dectin-1-Mediated Signaling.

Tissue resident intestinal macrophages are known to exhibit an anti-inflammatory phenotype and produce little pro-inflammatory cytokines upon TLR ligation, allowing symbiotic co-existence with the intestinal microbiota. However, upon acute events such as epithelial damage and concomitant influx of microbes, these macrophages must be able to quickly mount a pro-inflammatory response while more inflammatory macrophages are recruited from the blood stream simultaneously. Here, we show that dietary intake of vitamin A is required for the maintenance of the anti-inflammatory state of tissue resident intestinal macrophages. Interestingly, these anti-inflammatory macrophages were characterized by high levels of Dectin-1 expression. We show that Dectin-1 expression is enhanced by the vitamin A metabolite retinoic acid and our data suggests that Dectin-1 triggering might provide a switch to induce a rapid production of pro-inflammatory cytokines. In addition, Dectin-1 stimulation resulted in an altered metabolic profile which is linked to a pro-inflammatory response. Together, our data suggests that presence of vitamin A in the small intestine enhances an anti-inflammatory phenotype as well as Dectin-1 expression by macrophages and that this anti-inflammatory phenotype can rapidly convert toward a pro-inflammatory state upon Dectin-1 signaling.

Intestinal resident macrophages: Multitaskers of the gut

BackgroundIntestinal resident macrophages play a crucial role in homeostasis and have been implicated in numerous gastrointestinal diseases. While historically believed to be largely of hematopoietic origin, recent advances in fate‐mapping technology have unveiled the existence of long‐lived, self‐maintaining populations located in specific niches throughout the gut wall. Furthermore, the advent of single‐cell technology has enabled an unprecedented characterization of the functional specialization of tissue‐resident macrophages throughout the gastrointestinal tract.PurposeThe purpose of this review was to provide a panorama on intestinal resident macrophages, with particular focus to the recent advances in the field. Here, we discuss the functions and phenotype of intestinal resident macrophages and, where possible, the functional specialization of these cells in response to the niche they occupy. Furthermore, we will discuss their role in gastrointestinal diseases.

Unraveling the Pathogenesis of Inflammatory Bowel Disease and Search for New Therapeutic Medicines

The breakdown of the intestinal mucosal barrier has been shown to play a key role in the pathogenesis of intestinal immune-related disorders such as inflammatory bowel disease (IBD). IBD is a chronic inflammatory disorder with intermittent episodes of remission and relapse, and the incidence of IBD in Japan has risen dramatically in recent decades. Although sustained clinical remission has recently been recognized as an important goal of IBD therapy, there are not many treatment options to maintain long-term remission. Intestinal macrophages play pivotal roles in the regulation of immune homeostasis and inflammation in the intestine. Resident intestinal macrophages can regulate themselves and other immune cells, primarily through the spontaneous secretion of interleukin-10 (IL-10). We reported that the enhancement of IL-10 production by intestinal macrophages has the potential to be a novel therapeutic mechanism for maintaining the remission of IBD. Thus, to develop new therapeutic medicines for IBD, we screened the Wakanyaku Library derived from medicinal herbs for the ability to enhance IL-10 production by intestinal macrophages. Some compounds were identified with the potential to enhance IL-10 production by intestinal macrophages and thereby maintain long-term remission in IBD. This review focuses on our recent findings on the role of intestinal macrophages in the pathogenesis of IBD and developing a novel therapeutic strategy aimed at maintaining remission in IBD.

Macrophage interactions with fungi and bacteria in inflammatory bowel disease.

In this review, we discuss recent advances into delineating the dual role of intestinal phagocytes in health and during intestinal disease. We further discuss the key role of gut-resident macrophages in recognition of bacterial and fungal microbiota in the gut. Inflammatory bowel disease (IBD) commonly manifests with pathologic changes in the composition of gut bacterial and fungal microbiota. Intestinal macrophages are key regulators of the balance between tolerogenic immunity and inflammation. Recent studies have highlighted the role of resident intestinal macrophages in the control of commensal fungi and bacteria in the steady state and during dysbiosis. The dual role of these cells in maintaining intestinal homeostasis and responding to microbiota dysbiosis during inflammation is being increasingly studied. It is becoming increasingly clear that an aberrant proinflammatory response to microbiota by infiltrating monocytes plays a role in the development of intestinal inflammation. Intestinal mononuclear phagocytes with characteristics of macrophages play an important role in limiting fungal and bacterial overgrowth under these conditions, but can be influenced by the inflammatory environment to further propel inflammation. Better understanding of the interaction of intestinal macrophages with host microbiota including commensal fungi and bacteria, provides an opportunity for the development of more targeted therapies for IBD.

The role of adjuvant probiotics to attenuate intestinal inflammatory responses due to cancer treatments.

Chemotherapy and radiotherapy treatment regimens for gastrointestinal, peritoneal and pelvic tumours can disrupt the intestinal microbiome and intestinal epithelia. Such disturbances can provoke symptoms such as diarrhoea, nausea and vomiting. Chemotherapy and radiotherapy induced gastrointestinal toxicity aggravating intestinal microbiome dysbiosis is postulated to adversely alter the intestinal microbiome, with a consequent induced pro-inflammatory effect that disrupts the intestinal microbiome-epithelia-mucosal immunity axis. Although not widely recognised, the intestinal mucosa is the largest and most densely and dynamically populated immune-environment. Cancer treatment adverse effects that affect intestinal and mucosal cells inadvertently target and disrupt resident intestinal macrophages, the cells that marshal immune activity in the intestinal mucosa by shaping pro-inflammatory and anti-inflammatory activities to control and eradicate infectious insults and maintain local homeostasis. Pathobionts (bacteria capable of pathogenic pro-inflammatory activity) and noxious environmental and bacterial antigens use the intestinal epithelia and gap junctions as a point of entry into the systemic circulation. This translocation movement promotes toxic sequelae that obstruct intestinal macrophage functions resulting in uncontrolled local and systemic pro-inflammatory activity, loss of phagocytic function and loss of expression of tight junction proteins. Probiotic bacteria as an adjunctive treatment shows efficacy in ameliorating enteropathies such as mucositis/diarrhoea resulting from chemotherapy or radiotherapy regimens. As such we posit that an important benefit that warrants a further focused research effort is the administration of adjuvant probiotics to help reduce the incidence of febrile neutropenia.

The Brain-Intestinal Mucosa-Appendix- Microbiome-Brain Loop.

The brain and the gut are connected from early fetal life. The mother’s exposure to microbial molecules is thought to exert in utero developmental effects on the fetus. These effects could importantly underpin the groundwork for subsequent pathophysiological mechanisms for achieving immunological tolerance and metabolic equilibrium post birth, events that continue through to 3–4 years of age. Furthermore, it is understood that the microbiome promotes cues that instruct the neonate’s mucosal tissues and skin in the language of molecular and cellular biology. Post birth mucosal lymphoid tissue formation and maturation (most probably including the vermiform appendix) is microbiota-encouraged co-establishing the intestinal microbiome with a developing immune system. Intestinal mucosal tissue maturation loops the brain-gut-brain and is postulated to influence mood dispositions via shifts in the intestinal microbiome phyla. A plausible appreciation is that dysregulated pro-inflammatory signals from intestinal resident macrophages could breach the loop by providing adverse mood signals via vagus nerve afferents to the brain. In this commentary, we further suggest that the intestinal resident macrophages act as an upstream traffic controller of translocated microbes and metabolites in order to maintain local neuro-endocrine-immunological equilibrium. When macrophages are overwhelmed through intestinal microbiome and intestinal epithelial cell dysbiosis, pro-inflammatory signals are sustained, which may then lead to mood disorders. The administration of probiotics as an adjunctive medicine co-administered with antidepressant medications in improving depressed mood may have biological and clinical standing.

Diet-dependent, microbiota-independent regulation of IL-10-producing lamina propria macrophages in the small intestine.

Intestinal resident macrophages (Mϕs) regulate gastrointestinal homeostasis via production of an anti-inflammatory cytokine interleukin (IL)-10. Although a constant replenishment by circulating monocytes is required to maintain the pool of resident Mϕs in the colonic mucosa, the homeostatic regulation of Mϕ in the small intestine (SI) remains unclear. Here, we demonstrate that direct stimulation by dietary amino acids regulates the homeostasis of intestinal Mϕs in the SI. Mice that received total parenteral nutrition (TPN), which deprives the animals of enteral nutrients, displayed a significant decrease of IL-10-producing Mϕs in the SI, whereas the IL-10-producing CD4+ T cells remained intact. Likewise, enteral nutrient deprivation selectively affected the monocyte-derived F4/80+ Mϕ population, but not non-monocytic precursor-derived CD103+ dendritic cells. Notably, in contrast to colonic Mϕs, the replenishment of SI Mϕs and their IL-10 production were not regulated by the gut microbiota. Rather, SI Mϕs were directly regulated by dietary amino acids. Collectively, our study highlights the diet-dependent, microbiota-independent regulation of IL-10-producing resident Mϕs in the SI.

Neuro-Anatomical Evidence Indicating Indirect Modulation of Macrophages by Vagal Efferents in the Intestine but Not in the Spleen

BackgroundElectrical stimulation of the vagus nerve suppresses intestinal inflammation and normalizes gut motility in a mouse model of postoperative ileus. The exact anatomical interaction between the vagus nerve and the intestinal immune system remains however a matter of debate. In the present study, we provide additional evidence on the direct and indirect vagal innervation of the spleen and analyzed the anatomical evidence for neuroimmune modulation of macrophages by vagal preganglionic and enteric postganglionic nerve fibers within the intestine.MethodsDextran conjugates were used to label vagal preganglionic (motor) fibers projecting to the small intestine and spleen. Moreover, identification of the neurochemical phenotype of the vagal efferent fibers and enteric neurons was performed by immunofluorescent labeling. F4/80 antibody was used to label resident macrophages.ResultsOur anterograde tracing experiments did not reveal dextran-labeled vagal fibers or terminals in the mesenteric ganglion or spleen. Vagal efferent fibers were confined within the myenteric plexus region of the small intestine and mainly endings around nNOS, VIP and ChAT positive enteric neurons. nNOS, VIP and ChAT positive fibers were found in close proximity of intestinal resident macrophages carrying α7 nicotinic receptors. Of note, VIP receptors were found on resident macrophages located in close proximity of VIP positive nerve fibers.ConclusionIn the present study, we show that the vagus nerve does not directly interact with resident macrophages in the gut or spleen. Instead, the vagus nerve preferentially interacts with nNOS, VIP and ChAT enteric neurons located within the gut muscularis with nerve endings in close proximity of the resident macrophages.

Nitric oxide-mediated injury of interstitial cells of Cajal and intestinal dysmotility under endotoxemia of mice.

Gastrointestinal dysmotility is frequently observed under septic conditions, yet its precise mechanisms remain to be elucidated. In this study, we have investigated the mechanisms of intestinal dysmotility by lipopolysaccharides (LPS) and the role of the interstitial cells of Cajal (ICCs) in motility disorders using a mouse endotoxin model. The injection of LPS caused time- and dose-dependent decreases in the intestinal contractility, which was associated with similar time- and dose-dependent decreases in the number of KIT-positive fibroblast-like cells located in the intermuscular layer. iNOS inhibitors, L-NAME and aminoguanidine (AG), but not 7-nitroindazole (7NI), a specific nNOS inhibitor, inhibited the LPS-induced decreases in both the contractility and the number of KIT-positive cells. A spontaneous NO releaser, FK409, not only diminished spontaneous electrical potential and phasic contractions, but also decreased the number of KIT-positive cells. Pretreatment with gadolinium inhibited the activation of macrophages and the induction of iNOS in intestinal resident macrophages, and restored the number of KIT-positive cells and intestinal contractions. These results suggested that NO produced from intestinal macrophages via iNOS induced by LPS, may be involved in the ICCs injury and intestinal dysmotility under septic conditions.

A distinct vagal anti-inflammatory pathway modulates intestinal muscularis resident macrophages independent of the spleen

The cholinergic anti-inflammatory pathway (CAIP) has been proposed as a key mechanism by which the brain, through the vagus nerve, modulates the immune system in the spleen. Vagus nerve stimulation...

Context dependent differentiation of resident and inflammatory intestinal macrophages from a common monocyte precursor (120.1)

Abstract Macrophages (mϕ) are essential for homeostasis and protective immunity in the intestine, but also drive pathology in inflammatory bowel disease. It is not clear whether these different functions are due to distinct populations of mϕ, or if the same cell change. We show here that two populations of mϕ exist within the mouse colon, based on the levels of CX3CR1 expression. Most resting mϕ express CX3CR1 at much higher levels than any other tissue mϕ and also express CD11c. These resident mϕ produce a balanced mixture of TNFα and IL10 constitutively, but respond poorly to stimulation via TLR, despite expressing all TLR. During acute DSS colitis, mϕ expressing lower levels of CX3CR1 come to dominate. These “inflammatory” mϕ produce TNFα predominantly and respond via TLR. Using a combination of gene profiling, immunophenotyping and adoptive transfer models, we show that CX3CR1int mϕ in both healthy and inflamed intestine are derived from Ly6Chi CCR2+ monocytes that upregulate CX3CR1 after entering the intestine, sequentially acquiring F4/80 and class II MHC expression. Under resting but not inflammatory conditions, the newly arrived monocytes differentiate further, becoming CX3CR1hi, producing IL10, expressing CD163 and CD206 and becoming TLR unresponsive. These results provide novel evidence that “resident” and “inflammatory” mϕ in the intestine derive from the same monocyte precursor whose ultimate fate is determined locally and depends on the presence or absence of inflammation

EP2and EP4receptors on muscularis resident macrophages mediate LPS-induced intestinal dysmotility via iNOS upregulation through cAMP/ERK signals

Intestinal resident macrophages play an important role in gastrointestinal dysmotility by producing prostaglandins (PGs) and nitric oxide (NO) in inflammatory conditions. The causal correlation between PGs and NO in gastrointestinal inflammation has not been elucidated. In this study, we examined the possible role of PGE2 in the LPS-inducible inducible NO synthase (iNOS) gene expression in murine distal ileal tissue and macrophages. Treatment of ileal tissue with LPS increased the iNOS and cyclooxygenase (COX)-2 gene expression, which lead to intestinal dysmotility. However, LPS did not induce the expression of iNOS and COX-2 in tissue from macrophage colony-stimulating factor-deficient op/op mice, indicating that these genes are expressed in intestinal resident macrophages. iNOS and COX-2 protein were also expressed in dextran-phagocytized macrophages in the muscle layer. CAY10404, a COX-2 inhibitor, diminished LPS-dependent iNOS gene upregulation in wild-type mouse ileal tissue and also in RAW264.7 macrophages, indicating that PGs upregulate iNOS gene expression. EP2 and EP4 agonists upregulated iNOS gene expression in ileal tissue and isolated resident macrophages. iNOS mRNA induction mediated by LPS was decreased in the ileum isolated from EP2 or EP4 knockout mice. In addition, LPS failed to decrease the motility of EP2 and EP4 knockout mice ileum. EP2- or EP4-mediated iNOS expression was attenuated by KT-5720, a PKA inhibitor and PD-98059, an ERK inhibitor. Forskolin or dibutyryl-cAMP mimics upregulation of iNOS gene expression in macrophages. In conclusion, COX-2-derived PGE2 induces iNOS expression through cAMP/ERK pathways by activating EP2 and EP4 receptors in muscularis macrophages. NO produced in muscularis macrophages induces dysmotility during gastrointestinal inflammation.

Effects of bacterial products on enterocyte–macrophage interactions in vitro

We describe a coculture model of a human intestinal epithelial cell line and human peripheral blood monocytes in which monocytes differentiate into cells with features of resident intestinal macrophages. Caco-2 cells are grown on the lower surface of a semipermeable filter with pore size of 3μm (Transwells®) until they differentiate into enterocytes. Peripheral-blood monocytes are added and the co-culture incubated for two days. Monocytes migrate through the pores of the membrane, come into direct contact with the basolateral surfaces of the epithelial cell monolayer, and develop characteristics of resident intestinal macrophages including downregulation of CD14 expression and reduced pro-inflammatory cytokine responses (IL-8, TNF and IL-1β) to bacterial products. The apical application of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) resulted in an increased number of integrated monocytes, but abrogated the downregulation of CD14 expression and the diminished cytokine responses. MDP also reduced tight-junctional integrity, whilst LPS had no effect. These data indicate that LPS and MDP have significant pathophysiological effects on enterocyte–monocyte interactions, and confirm other studies that demonstrate that enterocytes and their products influence monocyte differentiation. This model may be useful in providing insights into the interaction between monocytes, epithelial cells and intestinal bacteria in health and disease.