Isolation and purification of CD14-negative mucosal macrophages from normal human small intestine

Mitochondrial dysfunction-associated microbiota establishes a transmissible refractory response to anti-TNF therapy during ulcerative colitis

Anti-TNF therapy can induce and maintain a remission status during intestinal bowel disease. However, up to 30% of patients do not respond to this therapy by mechanisms that are unknown. Here, we show that the absence of MCJ, a natural inhibitor of the respiratory chain Complex I, induces gut microbiota changes that are critical determinants of the lack of response in a murine model of DSS-induced inflammation. First, we found that MCJ expression is restricted to macrophages in human colonic tissue. Therefore, we demonstrate by transcriptomic analysis of colon macrophages from DSS-induced mice that MCJ-deficiency is linked to the expression of genes belonging to the FcγR signaling pathway and contains an anti-TNF refractory gene signature identified in ulcerative colitis patients. The gut microbial composition changes observed upon DSS treatment in the MCJ-deficient mice revealed the increased presence of specific colitogenic members, including Ruminococcus gnavus and Oscillospira, which could be associated with the non-response to TNF inhibitors. Further, we show that the presence of a microbiota associated resistance to treatment is dominant and transmissible to responsive individuals. Collectively, our findings underscore the critical role played by macrophage mitochondrial function in the gut ecological niche that can substantially affect not only the severity of inflammation but also the ability to successfully respond to current therapies.

Pathophysiology of Inflammatory Bowel Disease: Innate Immune System

Inflammatory bowel disease (IBD), comprising Crohn's disease (CD) and ulcerative colitis (UC), is a heterogeneous state of chronic intestinal inflammation with no exact known cause. Intestinal innate immunity is enacted by neutrophils, monocytes, macrophages, and dendritic cells (DCs), and innate lymphoid cells and NK cells, characterized by their capacity to produce a rapid and nonspecific reaction as a first-line response. Innate immune cells (IIC) defend against pathogens and excessive entry of intestinal microorganisms, while preserving immune tolerance to resident intestinal microbiota. Changes to this equilibrium are linked to intestinal inflammation in the gut and IBD. IICs mediate host defense responses, inflammation, and tissue healing by producing cytokines and chemokines, activating the complement cascade and phagocytosis, or presenting antigens to activate the adaptive immune response. IICs exert important functions that promote or ameliorate the cellular and molecular mechanisms that underlie and sustain IBD. A comprehensive understanding of the mechanisms underlying these clinical manifestations will be important for developing therapies targeting the innate immune system in IBD patients. This review examines the complex roles of and interactions among IICs, and their interactions with other immune and non-immune cells in homeostasis and pathological conditions.

Isolation and immortalization of macrophages derived from fetal porcine small intestine and their susceptibility to porcine viral pathogen infections

Macrophages are a heterogeneous population of cells that are present in all vertebrate tissues. They play a key role in the innate immune system, and thus, in vitro cultures of macrophages provide a valuable model for exploring their tissue-specific functions and interactions with pathogens. Porcine macrophage cultures are often used for the identification and characterization of porcine viral pathogens. Recently, we have developed a simple and efficient method for isolating primary macrophages from the kidneys and livers of swine. Here, we applied this protocol to fetal porcine intestinal tissues and demonstrated that porcine intestinal macrophages (PIM) can be isolated from mixed primary cultures of porcine small intestine-derived cells. Since the proliferative capacity of primary PIM is limited, we attempted to immortalize them by transferring the SV40 large T antigen and porcine telomerase reverse transcriptase genes using lentiviral vectors. Consequently, immortalized PIM (IPIM) were successfully generated and confirmed to retain various features of primary PIM. We further revealed that IPIM are susceptible to infection by the African swine fever virus and the porcine reproductive and respiratory syndrome virus and support their replication. These findings suggest that the IPIM cell line is a useful tool for developing in vitro models that mimic the intestinal mucosal microenvironments of swine, and for studying the interactions between porcine pathogens and host immune cells.

Identification of CX3CR1+ mononuclear phagocyte subsets involved in HIV-1 and SIV colorectal transmission

The difficulty to unambiguously identify the various subsets of mononuclear phagocytes (MNPs) of the intestinal lamina propria has hindered our understanding of the initial events occurring after mucosal exposure to HIV-1.

Here, we compared the composition and function of MNP subsets at steady-state and following ex vivo and in vivo viral exposure in human and macaque colorectal tissues.

Combined evaluation of CD11c, CD64, CD103, and CX3CR1 expression allowed to differentiate lamina propria MNPs subsets common to both species. Among them, CD11c⁺ CX3CR1⁺ cells expressing CCR5 migrated inside the epithelium following ex vivo and in vivo exposure of colonic tissue to HIV-1 or SIV. In addition, the predominant population of CX3CR1^high macrophages present at steady-state partially shifted to CX3CR1^low macrophages as early as three days following in vivo SIV rectal challenge of macaques.

Our analysis identifies CX3CR1⁺ MNPs as novel players in the early events of HIV-1 and SIV colorectal transmission.

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Human and macaque intestinal MNPs show similar phenotype, localization, and function

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CX3CR1⁺ MNPs migrate inside the intestinal epithelium to sample HIV/SIV

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SIV infection alters the balance between CX3CR1^high and CX3CR1^low Mφs

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CX3CR1⁺ Mφs contribute to the breakdown of the intestinal barrier in HIV/SIV infection

Structural diversity, functional aspects and future therapeutic applications of human gut microbiome

The research on human gut microbiome, regarded as the black box of the human body, is still at the stage of infancy as the functional properties of the complex gut microbiome have not yet been understood. Ongoing metagenomic studies have deciphered that the predominant microbial communities belong to eubacterial phyla Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria, Cyanobacteria, Verrucomicrobia and archaebacterial phylum Euryarchaeota. The indigenous commensal microbial flora prevents opportunistic pathogenic infection and play undeniable roles in digestion, metabolite and signaling molecule production and controlling host's cellular health, immunity and neuropsychiatric behavior. Besides maintaining intestinal health via short-chain fatty acid (SCFA) production, gut microbes also aid in neuro-immuno-endocrine modulatory molecule production, immune cell differentiation and glucose and lipid metabolism. Interdependence of diet and intestinal microbial diversity suggests the effectiveness of pre- and pro-biotics in maintenance of gut and systemic health. Several companies worldwide have started potentially exploiting the microbial contribution to human health and have translated their use in disease management and therapeutic applications. The present review discusses the vast diversity of microorganisms playing intricate roles in human metabolism. The contribution of the intestinal microbiota to regulate systemic activities including gut-brain-immunity crosstalk has been focused. To the best of our knowledge, this review is the first of its kind to collate and discuss the companies worldwide translating the multi-therapeutic potential of human intestinal microbiota, based on the multi-omics studies, i.e. metagenomics and metabolomics, as ready solutions for several metabolic and systemic disorders.

Blockage of bacterial FimH prevents mucosal inflammation associated with Crohn's disease

BACKGROUND

An Escherichia coli (E. coli) pathotype with invasive properties, first reported by Darfeuille-Michaud and termed adherent-invasive E. coli (AIEC), was shown to be prevalent in up to half the individuals with Crohn's Disease (CD), suggesting that these bacteria could be involved in the pathophysiology of CD. Among the genes related to AIEC pathogenicity, fim has the potential to generate an inflammatory reaction from the intestinal epithelial cells and macrophages, as it interacts with TLR4, inducing the production of inflammatory cytokines independently of LPS. Therefore, targeting the bacterial adhesion of FimH-expressing bacteria seems a promising therapeutic approach, consisting of disarming bacteria without killing them, representing a selective strategy to suppress a potentially critical trigger of intestinal inflammation, without disturbing the intestinal microbiota.

RESULTS

We analyzed the metagenomic composition of the gut microbiome of 358 patients with CD from two different cohorts and characterized the presence of FimH-expressing bacteria. To assess the pathogenic role of FimH, we used human intestinal explants and tested a specific FimH blocker to prevent bacterial adhesion and associated inflammation. We observed a significant and disease activity-dependent enrichment of Enterobacteriaceae in the gut microbiome of patients with CD. Bacterial FimH expression was functionally confirmed in ileal biopsies from 65% of the patients with CD. Using human intestinal explants, we further show that FimH is essential for adhesion and to trigger inflammation. Finally, a specific FimH-blocker, TAK-018, inhibits bacterial adhesion to the intestinal epithelium and prevents inflammation, thus preserving mucosal integrity.

CONCLUSIONS

We propose that TAK-018, which is safe and well tolerated in humans, is a promising candidate for the treatment of CD and in particular in preventing its recurrence. Video abstract.

Fecal microbiota profile in patients with inflammatory bowel disease in Taiwan

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic inflammatory disease associated with complicated interaction between immune, gut microbiota, and environmental factors in a genetically vulnerable host. Dysbiosis is often seen in patients with IBD. We aimed to investigate the fecal microbiota in patients with IBD and compared them with a control group in Taiwan.

METHODS

In this cross-sectional study, we investigated fecal microbiota in 20 patients with IBD and 48 healthy controls. Fecal samples from both IBD patients and controls were analyzed by the next-generation sequencing method and relevant software.

RESULTS

The IBD group showed lower bacterial richness and diversity compared with the control group. The principal coordinate analysis also revealed the significant structural differences between the IBD group and the control group. These findings were consistent whether the analysis was based on an operational taxonomic unit or amplicon sequence variant. However, no significant difference was found when comparing the composition of fecal microbiota between ulcerative colitis (UC) and Crohn's disease (CD). Further analysis showed that Lactobacillus, Enterococcus, and Bifidobacterium were dominant in the IBD group, whereas Faecalibacterium and Subdoligranulum were dominant in the control group at the genus level. When comparing UC, CD, and control group, Lactobacillus, Bifidobacterium, and Enterococcus were identified as dominant genera in the UC group. Fusobacterium and Escherichia_Shigella were dominant in the CD group.

CONCLUSION

Compared with the healthy control, the IBD group showed dysbiosis with a significant decrease in both richness and diversity of gut microbiota.

The Role of the Microbiome in Driving RA-Related Autoimmunity

Once referred to as "normal commensal flora" the human microbiome plays an integral role between health and disease. The host mucosal surface replete with a multitude of immune cells is a vast arena constantly sensing and responding to antigen presentation and microbial by-products. It is this key role that may allow the microbiome to prime or protect the host from autoimmune disease. Rheumatoid arthritis (RA) is a chronic, disabling inflammatory condition characterized by a complex multifactorial etiology. The presence of certain genetic markers has been proven to increase susceptibility to RA however it does not guarantee disease development. Given low concordance rates demonstrated in monozygotic twin studies there is a clear implication for the involvement of external players in RA pathogenesis. Since the historical description of rheumatoid factor, numerous additional autoantibodies have been described in the sera of RA patients. The presence of anti-cyclic citrullinated protein antibody is now a standard test, and is associated with a more severe disease course. Interestingly these antibodies are detectable in patient's sera long before the clinical signs of RA occur. The production of autoantibodies is driven by the lack of tolerance of the immune system, and how tolerance is broken is a crucial question for understanding RA development. Here we review current literature on the role of the microbiome in RA development including periodontal, gut and lung mucosa, with particular focus on proposed mechanisms of host microbiome interactions. We discuss the use of Mendelian randomization to assign causality to the microbiome and present considerations for future studies.

At the Forefront of the Mucosal Barrier: The Role of Macrophages in the Intestine

Macrophages are part of the innate immunity and are key players for the maintenance of intestinal homeostasis. They belong to the group of mononuclear phagocytes, which exert bactericidal functions and help to clear apoptotic cells. Moreover, they play essential roles for the maintenance of epithelial integrity and tissue remodeling during wound healing processes and might be implicated in intestinal tumor development. Macrophages are antigen-presenting cells and secrete immune-modulatory factors, like chemokines and cytokines, which are necessary to activate other intestinal immune cells and therefore to shape immune responses in the gut. However, overwhelming activation or increased secretion of pro-inflammatory cytokines might also contribute to the pathogenesis of inflammatory bowel disease. Presently, intestinal macrophages are in the center of intense studies, which might help to develop new therapeutic strategies to counteract the development or treat already existing inflammatory diseases in the gut. In this review, we focus on the origin of intestinal macrophages and, based on current knowledge, discuss their role in the gut during homeostasis and inflammation, as well as during intestinal wound healing and tumor development.

How uterine microbiota might be responsible for a receptive, fertile endometrium

BACKGROUND

Fertility depends on a receptive state of the endometrium, influenced by hormonal and anatomical adaptations, as well as the immune system. Local and systemic immunity is greatly influenced by microbiota. Recent discoveries of 16S rRNA in the endometrium and the ability to detect low-biomass microbiota fueled the notion that the uterus may be indeed a non-sterile compartment. To date, the concept of the 'sterile womb' focuses on in utero effects of microbiota on offspring and neonatal immunity. However, little awareness has been raised regarding the importance of uterine microbiota for endometrial physiology in reproductive health; manifested in fertility and placentation.

OBJECTIVE AND RATIONALE

Commensal colonization of the uterus has been widely discussed in the literature. The objective of this review is to outline the possible importance of this uterine colonization for a healthy, fertile uterus. We present the available evidence regarding uterine microbiota, focusing on recent findings based on 16S rRNA, and depict the possible importance of uterine colonization for a receptive endometrium. We highlight a possible role of uterine microbiota for host immunity and tissue adaptation, as well as conferring protection against pathogens. Based on knowledge of the interaction of the mucosal immune cells of the gut with the local microbiome, we want to investigate the potential implications of commensal colonization for uterine health.

SEARCH METHODS

PubMed and Google Scholar were searched for articles in English indexed from 1 January 2008 to 1 March 2018 for '16S rRNA', 'uterus' and related search terms to assess available evidence on uterine microbiome analysis. A manual search of the references within the resulting articles was performed. To investigate possible functional contributions of uterine microbiota to health, studies on microbiota of other body sites were additionally assessed.

OUTCOMES

Challenging the view of a sterile uterus is in its infancy and, to date, no conclusions on a 'core uterine microbiome' can be drawn. Nevertheless, evidence for certain microbiota and/or associated compounds in the uterus accumulates. The presence of microbiota or their constituent molecules, such as polysaccharide A of the Bacteroides fragilis capsule, go together with healthy physiological function. Lessons learned from the gut microbiome suggest that the microbiota of the uterus may potentially modulate immune cell subsets needed for implantation and have implications for tissue morphology. Microbiota can also be crucial in protection against uterine infections by defending their niche and competing with pathogens. Our review highlights the need for well-designed studies on a 'baseline' microbial state of the uterus representing the optimal starting point for implantation and subsequent placenta formation.

WIDER IMPLICATIONS

The complex interplay of processes and cells involved in healthy pregnancy is still poorly understood. The correct receptive endometrial state, including the local immune environment, is crucial not only for fertility but also placenta formation since initiation of placentation highly depends on interaction with immune cells. Implantation failure, recurrent pregnancy loss, and other pathologies of endometrium and placenta, such as pre-eclampsia, represent an increasing societal burden. More robust studies are needed to investigate uterine colonization. Based on current data, future research needs to include the uterine microbiome as a relevant factor in order to understand the players needed for healthy pregnancy.

Gender-related differences observed among immune cells in synovial fluid in knee osteoarthritis

OBJECTIVE

There is no existing comprehensive report on the cellular composition of synovial fluids (SFs) from knee osteoarthritis (OA). We therefore aimed to characterise the immune cell composition in SFs from knee OA (KOA) and in subgroups according to gender.

DESIGN

The immunophenotyping of monocyte/macrophage lineage cells, T and B cells, NK cells, neutrophils, dendritic and mast cells (MC) present in SFs from 53 patients (24 males/29 females) with KOA was performed using 6-colour flow cytometry.

RESULTS

SFs from patients with OA contained 90% hematopoietic cells. Lymphocytes were the predominant cell population (44.8%) in the SFs of OA patients, with CD4⁺ T lymphocytes being more prevalent than CD8⁺ T cells (CD4⁺/CD8⁺ ratio = 1.3). Within the monocyte/macrophage lineage gating, monocytes accounted for 33.9%, macrophages 14.8%, myeloid dendritic cells 16.4%. The rest of the hematopoietic cells were comprised of neutrophils (8%), NK cells (3.8%), T regulatory cells (1.2%), plasmacytoid dendritic cells (1.1%), mast cells (0.3%). In OA females, a higher percentage of CD4⁺ T cells (P = 0.023), macrophages (P = 0.012), and a lower percentage of monocytes (P = 0.008) and CD8⁺ T cells (P = 0.002) were detected in comparison to OA males.

CONCLUSIONS

Based on the immune cell composition of SFs, data mining analysis revealed distinct phenotypes (monocyte- and lymphocyte-predominant) within each gender group. This first study on the cellular complexity of SFs in KOA showed marked differences between male and female patients. The findings give a rational starting point for patient stratification according to their phenotypes, as is required for phenotype-specific treatment strategies.

Liver macrophage-associated inflammation correlates with SIV burden and is substantially reduced following cART

Liver disease is a leading contributor to morbidity and mortality during HIV infection, despite the use of combination antiretroviral therapy (cART). The precise mechanisms of liver disease during HIV infection are poorly understood partially due to the difficulty in obtaining human liver samples as well as the presence of confounding factors (e.g. hepatitis co-infection, alcohol use). Utilizing the simian immunodeficiency virus (SIV) macaque model, a controlled study was conducted to evaluate the factors associated with liver inflammation and the impact of cART. We observed an increase in hepatic macrophages during untreated SIV infection that was associated with a number of inflammatory and fibrosis mediators (TNFα, CCL3, TGFβ). Moreover, an upregulation in the macrophage chemoattractant factor CCL2 was detected in the livers of SIV-infected macaques that coincided with an increase in the number of activated CD16+ monocyte/macrophages and T cells expressing the cognate receptor CCR2. Expression of Mac387 on monocyte/macrophages further indicated that these cells recently migrated to the liver. The hepatic macrophage and T cell levels strongly correlated with liver SIV DNA levels, and were not associated with the levels of 16S bacterial DNA. Utilizing in situ hybridization, SIV-infected cells were found primarily within portal triads, and were identified as T cells. Microarray analysis identified a strong antiviral transcriptomic signature in the liver during SIV infection. In contrast, macaques treated with cART exhibited lower levels of liver macrophages and had a substantial, but not complete, reduction in their inflammatory profile. In addition, residual SIV DNA and bacteria 16S DNA were detected in the livers during cART, implicating the liver as a site on-going immune activation during antiretroviral therapy. These findings provide mechanistic insights regarding how SIV infection promotes liver inflammation through macrophage recruitment, with implications for in HIV-infected individuals.

An Alternatively Activated Macrophage Marker CD163 in Severely Obese Patients: the Influence of Very Low-Calorie Diet and Bariatric Surgery

CD163 is a marker of macrophages with anti-inflammatory properties and its soluble form (sCD163) is considered a prognostic predictor of several diseases including type 2 diabetes mellitus (T2DM). We explored sCD163 levels at baseline and after very low-calorie diet (VLCD) or bariatric surgery in 32 patients with obesity (20 undergoing VLCD and 12 bariatric surgery), 32 obese patients with T2DM (22 undergoing VLCD and 10 bariatric surgery), and 19 control subjects. We also assessed the changes of CD163 positive cells of monocyte-macrophage lineage in peripheral blood and subcutaneous adipose tissue (SAT) in subset of patients. Plasma sCD163 levels were increased in obese and T2DM subjects relative to control subjects (467.2±40.2 and 513.8±37.0 vs. 334.4±24.8 ng/ml, p=0.001) and decreased after both interventions. Obesity decreased percentage of CD163+CD14+ monocytes in peripheral blood compared to controls (78.9±1.48 vs. 86.2±1.31 %, p=0.003) and bariatric surgery decreased CD163+CD14+HLA-DR+ macrophages in SAT (19.4±2.32 vs. 11.3±0.90 %, p=0.004). Our data suggest that increased basal sCD163 levels are related to obesity and its metabolic complications. On the contrary, sCD163 or CD163 positive cell changes do not precisely reflect metabolic improvements after weight loss.

Blockade of CD14 aggravates experimental shigellosis

Shigella infections lead to severe inflammation associated with destruction of colonic mucosa. We assessed the effect of in vivo blockade of CD14 on the outcome of experimental Shigella infection in rabbits. A total of 17 rabbits were divided into two groups: 8 received a single i.v. dose of anti-rabbit CD14 monoclonal antibody prior to infection with an invasive Shigella flexneri strain; the remainder served as controls. The anti-CD14-treated rabbits exhibited more severe tissue destruction and a 50-fold increase in bacterial invasion of the intestinal mucosa when compared to controls. Similar numbers of polymorphonuclear leukocytes were recruited to the intestinal mucosa in both groups despite the massive bacterial invasion seen in the CD14-blocked group. No statistically significant differences were seen in levels of IL-1β nor in the ratio of IL-1RA/IL-1β for either group. In contrast, higher quantities of TNF-α were observed in the CD14-blocked group. To conclude, anti-CD14 treatment had a detrimental effect on the capacity of Shigella-infected animals to clear the infection.

Cytomegalovirus enhances macrophage TLR expression and MyD88-mediated signal transduction to potentiate inducible inflammatory responses

Circulating monocytes carrying human CMV (HCMV) migrate into tissues, where they differentiate into HCMV-infected resident macrophages that upon interaction with bacterial products may potentiate tissue inflammation. In this study, we investigated the mechanism by which HCMV promotes macrophage-orchestrated inflammation using a clinical isolate of HCMV (TR) and macrophages derived from primary human monocytes. HCMV infection of the macrophages, which was associated with viral DNA replication, significantly enhanced TNF-α, IL-6, and IL-8 gene expression and protein production in response to TLR4 ligand (LPS) stimulation compared with mock-infected LPS-stimulated macrophages during a 6-d in vitro infection. HCMV infection also potentiated TLR5 ligand-stimulated cytokine production. To elucidate the mechanism by which HCMV infection potentiated inducible macrophage responses, we show that infection by HCMV promoted the maintenance of surface CD14 and TLR4 and TLR5, which declined over time in mock-infected macrophages, and enhanced both the intracellular expression of adaptor protein MyD88 and the inducible phosphorylation of IκBα and NF-κB. These findings provide additional information toward elucidating the mechanism by which HCMV potentiates bacteria-induced NF-κB-mediated macrophage inflammatory responses, thereby enhancing organ inflammation in HCMV-infected tissues.

Gastrointestinal tract and the mucosal macrophage reservoir in HIV infection

The gastrointestinal tract (GIT) is a primary site for human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infection, replication, and dissemination. After an initial explosive phase of infection, HIV establishes latency. In addition to CD4 T cells, macrophages are readily infected, which can persist for long periods of time. Though macrophages at various systemic sites are infected, those present in the GIT constitute a major cellular reservoir due to the abundance of these cells at mucosal sites. Here, we review some of the important findings regarding what is known about the macrophage reservoir in the gut and explore potential approaches being pursued in the field to reduce this reservoir. The development of strategies that can lead to a functional cure will need to incorporate approaches that can eradicate the macrophage reservoir in the GIT.

Rapidly expanding knowledge on the role of the gut microbiome in health and disease

The human gut is colonized by a wide diversity of micro-organisms, which are now known to play a key role in the human host by regulating metabolic functions and immune homeostasis. Many studies have indicated that the genomes of our gut microbiota, known as the gut microbiome or our "other genome" could play an important role in immune-related, complex diseases, and growing evidence supports a causal role for gut microbiota in regulating predisposition to diseases. A comprehensive analysis of the human gut microbiome is thus important to unravel the exact mechanisms by which the gut microbiota are involved in health and disease. Recent advances in next-generation sequencing technology, along with the development of metagenomics and bioinformatics tools, have provided opportunities to characterize the microbial communities. Furthermore, studies using germ-free animals have shed light on how the gut microbiota are involved in autoimmunity. In this review we describe the different approaches used to characterize the human microbiome, review current knowledge about the gut microbiome, and discuss the role of gut microbiota in immune homeostasis and autoimmunity. Finally, we indicate how this knowledge could be used to improve human health by manipulating the gut microbiota. This article is part of a Special Issue entitled: From Genome to Function.

Initiation of an inflammatory response in resident intestinal lamina propria cells -use of a human organ culture model

Resident human lamina propria immune cells serve as powerful effectors in host defense. Molecular events associated with the initiation of an intestinal inflammatory response in these cells are largely unknown. Here, we aimed to characterize phenotypic and functional changes induced in these cells at the onset of intestinal inflammation using a human intestinal organ culture model. In this model, healthy human colonic mucosa was depleted of epithelial cells by EDTA treatment. Following loss of the epithelial layer, expression of the inflammatory mediators IL1B, IL6, IL8, IL23A, TNFA, CXCL2, and the surface receptors CD14, TLR2, CD86, CD54 was rapidly induced in resident lamina propria cells in situ as determined by qRT-PCR and immunohistology. Gene microarray analysis of lamina propria cells obtained by laser-capture microdissection provided an overview of global changes in gene expression occurring during the initiation of an intestinal inflammatory response in these cells. Bioinformatic analysis gave insight into signalling pathways mediating this inflammatory response. Furthermore, comparison with published microarray datasets of inflamed mucosa in vivo (ulcerative colitis) revealed a significant overlap of differentially regulated genes underlining the in vivo relevance of the organ culture model. Furthermore, genes never been previously associated with intestinal inflammation were identified using this model. The organ culture model characterized may be useful to study molecular mechanisms underlying the initiation of an intestinal inflammatory response in normal mucosa as well as potential alterations of this response in inflammatory bowel disease.

Stromal regulation of human gastric dendritic cells restricts the Th1 response to Helicobacter pylori

BACKGROUND & AIMS

Mucosal dendritic cells (DCs) play a key role in initiating the T-helper (Th)1 response to Helicobacter pylori. To further elucidate the mucosal response to H pylori, we examined whether gastric stromal factors condition DCs to support tolerance to H pylori, analogous to intestinal stromal factor-driven macrophage tolerance to commensal bacteria.

METHODS

To model mucosal DC development, we isolated and cultured cell-depleted human stroma/extracellular matrix from fresh gastric and intestinal mucosa to generate stroma-conditioned media. We then analyzed the capacity of stroma-conditioned media-treated monocyte-derived DCs and primary human gastric and intestinal DCs pulsed in vitro with H pylori to induce T-cell proliferation and interferon gamma secretion.

RESULTS

Stromal factors in gastric mucosa suppressed H pylori-stimulated DC activation and the ability of DCs to drive a Th1 proliferative and cytokine response to H pylori. The ability of gastric stromal factors to down-regulate DC function was similar to that of intestinal stromal factors and was independent of transforming growth factor β, prostaglandin E₂, interleukin (IL)-10, and thymic stromal lymphopoietin. Stroma-conditioned media-induced reduction in DC-stimulated Th1 responses was associated with reduced DC release of IL-12.

CONCLUSIONS

Gastric stromal factors down-regulate DC responsiveness to H pylori, resulting in a dampened gastric Th1 response. We speculate that stroma-induced down-regulation of DC function contributes to the permissiveness of both gastric and intestinal mucosa to colonization by persistent residential microbes.

Extracellular matrix-associated cytokines regulate CD4+ effector T-cell responses in the human intestinal mucosa

Extracellular matrix (stroma) regulation of mucosal T-cell function is incompletely understood. In this study, we uncovered a role for intestinal stromal products in the innate regulation of effector T cells. Stroma-conditioned media (S-CM) derived from the normal human intestinal stroma (transforming growth factor-β (TGF-β)(hi)/interleukin (IL)-6(lo)/IL-1β(lo)) significantly downregulated T-cell proliferation and interferon-γ (IFN-γ) production compared with S-CM derived from the inflamed Crohn's mucosa (TGF-β(hi)/IL-6(hi)/IL-1β(hi)). Antibody neutralization studies showed that TGF-β in normal S-CM inhibited T-cell proliferation and IFN-γ production, whereas IL-6 plus IL-1β in Crohn's S-CM promoted T-cell proliferation, and IL-1β alone promoted IFN-γ and IL-17 release. Importantly, normal S-CM inhibited T-bet expression, whereas Crohn's S-CM activated signal transducer and activator of transcription 3, suggesting that discordant T-cell responses are regulated at the transcription factor and signaling levels. These findings implicate stromal TGF-β in the downregulation of T-cell 2 responses in the normal intestinal mucosa, and stromal IL-6 and IL-1β in the promotion of Th1 and Th17 responses in the inflamed Crohn's mucosa, suggesting an innate regulatory function for the intestinal extracellular matrix.

Stromal down-regulation of macrophage CD4/CCR5 expression and NF-κB activation mediates HIV-1 non-permissiveness in intestinal macrophages

Tissue macrophages are derived exclusively from blood monocytes, which as monocyte-derived macrophages support HIV-1 replication. However, among human tissue macrophages only intestinal macrophages are non-permissive to HIV-1, suggesting that the unique microenvironment in human intestinal mucosa renders lamina propria macrophages non-permissive to HIV-1. We investigated this hypothesis using blood monocytes and intestinal extracellular matrix (stroma)-conditioned media (S-CM) to model the exposure of newly recruited monocytes and resident macrophages to lamina propria stroma, where the cells take up residence in the intestinal mucosa. Exposure of monocytes to S-CM blocked up-regulation of CD4 and CCR5 expression during monocyte differentiation into macrophages and inhibited productive HIV-1 infection in differentiated macrophages. Importantly, exposure of monocyte-derived macrophages simultaneously to S-CM and HIV-1 also inhibited viral replication, and sorted CD4⁺ intestinal macrophages, a proportion of which expressed CCR5⁺, did not support HIV-1 replication, indicating that the non-permissiveness to HIV-1 was not due to reduced receptor expression alone. Consistent with this conclusion, S-CM also potently inhibited replication of HIV-1 pseudotyped with vesicular stomatitis virus glycoprotein, which provides CD4/CCR5-independent entry. Neutralization of TGF-β in S-CM and recombinant TGF-β studies showed that stromal TGF-β inhibited macrophage nuclear translocation of NF-κB and HIV-1 replication. Thus, the profound inability of intestinal macrophages to support productive HIV-1 infection is likely the consequence of microenvironmental down-regulation of macrophage HIV-1 receptor/coreceptor expression and NF-κB activation.

Human intestinal macrophages, unlike lymphoid tissue macrophages, brain microglia and genital (vaginal) macrophages, are profoundly incapable of supporting productive HIV-1 infection. Intriguingly, all macrophages are derived exclusively from blood monocytes, which are HIV-1 permissive after differentiation into monocyte-derived macrophages. Therefore, the unique non-permissiveness of intestinal macrophages to HIV-1 must be conferred by the intestinal mucosal microenvironment. Here we report that intestinal stroma potently blocked up-regulation of HIV-1 receptor/coreceptor CD4 and CCR5 expression during monocyte differentiation into macrophages and macrophage nuclear translocation of NF-κB, which is a critical requirement for HIV-1 transcription. These two mechanisms work collaboratively to render intestinal macrophages non-permissive to HIV-1. Harnessing this natural antiviral defense may provide a novel strategy to exploit for the prevention of infection in HIV-1 permissive cells.

Intestinal macrophages and response to microbial encroachment

Macrophages in the gastrointestinal mucosa represent the largest pool of tissue macrophages in the body. In order to maintain mucosal homeostasis, resident intestinal macrophages uniquely do not express the lipopolysaccharide (LPS) co-receptor CD14 or the IgA (CD89) and IgG (CD16, 32, and 64) receptors, yet prominently display Toll-like receptors (TLRs) 3-9. Remarkably, intestinal macrophages also do not produce proinflammatory cytokines in response to TLR ligands, likely because of extracellular matrix (stromal) transforming growth factor-β (TGF-β) dysregulation of nuclear factor (NF)-κB signal proteins and, via Smad signaling, expression of IκBα, thereby inhibiting NF-κB-mediated activities. Thus, in noninflamed mucosa, resident macrophages are inflammation anergic but retain avid scavenger and host defense function, an ideal profile for macrophages in close proximity to gut microbiota. In the event of impaired epithelial integrity during intestinal infection or inflammation, however, blood monocytes also accumulate in the lamina propria and actively pursue invading microorganisms through uptake and degradation of the organism and release of inflammatory mediators. Consequently, resident intestinal macrophages are inflammation adverse, but when the need arises, they receive assistance from newly recruited circulating monocytes.

The role of the macrophage in sentinel responses in intestinal immunity

PURPOSE OF REVIEW

The purpose of this review is to highlight macrophages as central mediators of intestinal immune homeostasis and inflammation.

RECENT FINDINGS

We review recent developments elucidating distinct phenotypic adaptations in intestinal macrophages that determine their functional role in a microbe-rich environment. The involvement of intestinal macrophages in the pathogenesis of inflammatory bowel disease is also discussed.

SUMMARY

Intestinal macrophages represent the largest pool of tissue macrophages in the human body and a critical interface with the enteric microbiota. In normal physiology, luminal microbes breach the intestinal epithelial barrier and gain access to the lamina propria. Bacteria are efficiently phagocytosed by macrophages strategically located underneath the epithelium. The importance of functional adaptations of macrophages to perform their role in this unique environment is best illustrated by failure of these mechanisms during the development of chronic inflammatory bowel diseases. Compared with monocytes or macrophages from any other organ, intestinal macrophages express different phenotypic markers, efficiently eradicate intracellular bacteria, but do not mount potent inflammatory responses. Converging human genetic and functional findings suggest that dysregulation of macrophage-specific immune responses against an otherwise harmless enteric microbiota are key factors in the pathogenesis of inflammatory bowel disease.

Inflammation anergy in human intestinal macrophages is due to Smad-induced IkappaBalpha expression and NF-kappaB inactivation

Human intestinal macrophages contribute to tissue homeostasis in noninflamed mucosa through profound down-regulation of pro-inflammatory cytokine release. Here, we show that this down-regulation extends to Toll-like receptor (TLR)-induced cytokine release, as intestinal macrophages expressed TLR3-TLR9 but did not release cytokines in response to TLR-specific ligands. Likely contributing to this unique functional profile, intestinal macrophages expressed markedly down-regulated adapter proteins MyD88 and Toll interleukin receptor 1 domain-containing adapter-inducing interferon beta, which together mediate all TLR MyD88-dependent and -independent NF-kappaB signaling, did not phosphorylate NF-kappaB p65 or Smad-induced IkappaBalpha, and did not translocate NF-kappaB into the nucleus. Importantly, transforming growth factor-beta released from intestinal extracellular matrix (stroma) induced identical down-regulation in the NF-kappaB signaling and function of blood monocytes, the exclusive source of intestinal macrophages. Our findings implicate stromal transforming growth factor-beta-induced dysregulation of NF-kappaB proteins and Smad signaling in the differentiation of pro-inflammatory blood monocytes into noninflammatory intestinal macrophages.

Human primary gastric dendritic cells induce a Th1 response to H. pylori

Adaptive CD4 T-cell responses are important in the pathogenesis of chronic Helicobacter pylori gastritis. However, the gastric antigen-presenting cells that induce these responses have not yet been identified. Here we show that dendritic cells (DCs) are present in the gastric mucosa of healthy subjects and are more prevalent and more activated in the gastric mucosa of H. pylori-infected subjects. H. pylori induced gastric DCs isolated from noninfected subjects to express increased levels of CD11c, CD86 and CD83, and to secrete proinflammatory cytokines, particularly interleukin (IL)-6 and IL-8. Importantly, gastric DCs pulsed with live H. pylori, but not control DCs, mediated T-cell secretion of interferon-gamma. The ability of H. pylori to induce gastric DC maturation and stimulate gastric DC activation of Th1 cells implicates gastric DCs as initiators of the immune response to H. pylori.

Dendritic cells transmit HIV-1 through human small intestinal mucosa

To dissect the early events in the transmission of HIV-1 from mother to child, we investigated whether DCs participate in HIV-1 entry into human small intestinal mucosa. We isolated human MNLs from jejunal lamina propria and identified a subpopulation of CD11c(+)HLA-DR(+) MNLs that expressed DC-SIGN, CD83, CD86, CD206, and CCR7, indicating a DC phenotype. Jejunal DCs also expressed the HIV-1 receptor CD4 and coreceptors CCR5 and CXCR4 and in suspension rapidly took up cell-free HIV-1. HIV-1 inoculated onto the apical surface of explanted jejunum was transported by lamina propria DCs through the mucosa and transmitted in trans to blood and intestinal lymphocytes. These findings indicate that in addition to intestinal epithelial cells, which we showed previously transcytose infectious HIV-1 to indicator cells, intestinal DCs play an important role in transporting HIV-1 through the intestinal mucosa and the subsequent transmission to T cells.

Intestinal macrophages: differentiation and involvement in intestinal immunopathologies

Intestinal macrophages, preferentially located in the subepithelial lamina propria, represent the largest pool of tissue macrophages in humans. As an adaptation to the local antigen- and bacteria-rich environment, intestinal macrophages exhibit several distinct phenotypic and functional characteristics. Notably, microbe-associated molecular pattern receptors, including the lipopolysaccharide (LPS) receptors CD14 and TLR4, and also the Fc receptors for IgA and IgG are absent on most intestinal macrophages under homeostatic conditions. Moreover, while macrophages in the intestinal mucosa are refractory to the induction of proinflammatory cytokine secretion, they still display potent phagocytic activity. These adaptations allow intestinal macrophages to comply with their main task, i.e., the efficient removal of microbes while maintaining local tissue homeostasis. In this paper, we review recent findings on the functional differentiation of monocyte subsets into distinct macrophage populations and on the phenotypic and functional adaptations that have evolved in intestinal macrophages in response to their antigen-rich environment. Furthermore, the involvement of intestinal macrophages in the pathogenesis of celiac disease and inflammatory bowel diseases is discussed.

Involvement of dendritic cells in the pathogenesis of inflammatory bowel disease

In conclusion, during inflammation, DCs are likely activated by inflammatory signals and induced to migrate to T cell zones of organized lymphoid tissues where the cells induce T cell responses. In addition to their established role in T cell priming and the induction of tolerance, DCs may act to enhance (or possibly suppress) T cell responses at sites of mucosal inflammation. Determining the importance of DCs in this regard, as well as establishing a potential role for DCs in continuous activation of naive or central memory cells in lymph nodes draining inflammatory sites, will elucidate the role of DCs as a potential therapeutic target for chronic inflammatory diseases, like IBD. Resident intestinal macrophages are noninflammatory and do not efficiently present antigens to intestinal T cells, yet are avidly phagocytic and able to kill internalized organisms. During intestinal inflammation, monocytes are recruited from the blood, become inflammatory macrophages in the inflamed tissue, and are major contributors to tissue destruction and perpetuation of inflammation via their production of chemokines and pro-inflammatory cytokines. Macrophages may also contribute directly to DC activation and maturation, which would drive DCs to present antigens from the bacterial flora to T cells locally within tissue or to more efficiently traffic to T cell zones of lymphoid tissue. Thus, DCs and macrophages have evolved functional niches that promote cooperation in the prevention of untoward intestinal inflammation in the steady state and in the eradication of invasive microorganisms during infection. The balance between suppressing inflammation and promoting host defense is altered in humans with IBD allowing a persistent inflammatory response to commensal bacteria. Based on studies from animal models, the pathogenesis of IBD likely involves either the lack of appropriate regulation from T cells, or an over-production of effector T cells. The end result of these potential mechanisms is the abnormal induction and/or survival of effector T cells and the production of factors such as cytokines by inflammatory macrophages and neutrophils that result in tissue destruction. The destructive process likely involves normally tolerizing DCs, which in the microenvironment of the inflamed mucosa activate T cell responses to normal flora in both draining lymphoid tissues and at sites of inflammation, with macrophages and neutrophils contributing the bulk of inflammatory and destructive cytokines.

Macrophages in vaginal but not intestinal mucosa are monocyte-like and permissive to human immunodeficiency virus type 1 infection

Mucosal surfaces play a major role in human immunodeficiency virus type 1 (HIV-1) transmission and pathogenesis, and yet the role of lamina propria macrophages in mucosal HIV-1 infection has received little investigative attention. We report here that vaginal and intestinal macrophages display distinct phenotype and HIV-1 permissiveness profiles. Vaginal macrophages expressed the innate response receptors CD14, CD89, CD16, CD32, and CD64 and the HIV-1 receptor/coreceptors CD4, CCR5, and CXCR4, similar to monocytes. Consistent with this phenotype, green fluorescent protein-tagged R5 HIV-1 entered macrophages in explanted vaginal mucosa as early as 30 min after inoculation of virus onto the epithelium, and purified vaginal macrophages supported substantial levels of HIV-1 replication by a panel of highly macrophage-tropic R5 viruses. In sharp contrast, intestinal macrophages expressed no detectable, or very low levels of, innate response receptors and HIV-1 receptor/coreceptors and did not support HIV-1 replication, although virus occasionally entered macrophages in intestinal tissue explants. Thus, vaginal, but not intestinal, macrophages are monocyte-like and permissive to R5 HIV-1 after the virus has translocated across the epithelium. These findings suggest that genital and gut macrophages have different roles in mucosal HIV-1 pathogenesis and that vaginal macrophages play a previously underappreciated but potentially important role in mucosal HIV-1 infection in the female genital tract.

Quantitative isolation of mouse and human intestinal intraepithelial lymphocytes by elutriation centrifugation

Intestinal intraepithelial lymphocytes (IEL) are specialized subsets of T cells with distinct functional capacities. While some IEL subsets are circulating, others such as CD8alphaalpha TCRalphabeta IEL are believed to represent non-circulating resident T cell subsets [Sim, G.K., Intraepithelial lymphocytes and the immune system. Adv. Immunol., 1995. 58: 297-343.]. Current methods to obtain enriched preparations of intraepithelial lymphocytes are mostly based on Percoll density gradient or magnetic bead-based technologies [Lundqvist, C., et al., Isolation of functionally active intraepithelial lymphocytes and enterocytes from human small and large intestine. J. Immunol. Methods, 1992. 152(2): 253-263.]. However, these techniques are hampered by a generally low yield of isolated cells, and potential artifacts due to the interference of the isolation procedure with subsequent functional assays, in particular, when antibodies against cell surface markers are required. Here we describe a new method for obtaining relatively pure populations of intestinal IEL (55-75%) at a high yield (>85%) by elutriation centrifugation. This technique is equally suited for the isolation and enrichment of intraepithelial lymphocytes of both mouse and human origin. Time requirements for fractionating cell suspensions by elutriation centrifugation are comparable to Percoll-, or MACS-based isolation procedures. Hence, the substantially higher yield and the consistent robust enrichment for intraepithelial lymphocytes, together with the gentle treatment of the cells during elutriation that does not interfere with subsequent functional assays, are important aspects that are in favor of using this elegant technology to obtain unmanipulated, unbiased populations of intestinal intraepithelial lymphocytes, and, if desired, also of pure epithelial cells.

Epithelial and mesenchymal cells in the bovine colonic mucosa differ in their responsiveness to Escherichia coli Shiga toxin 1

Bovine colonic crypt cells express CD77 molecules that potentially act as receptors for Shiga toxins (Stx). The implication of this finding for the intestinal colonization of cattle by human pathogenic Stx-producing Escherichia coli (STEC) remains undefined. We used flow cytometric and real-time PCR analyses of primary cultures of colonic crypt cells to evaluate cell viability, CD77 expression, and gene transcription in the presence and absence of purified Stx1. A subset of cultured epithelial cells had Stx receptors which were located mainly intracellularly, with a perinuclear distribution, and were resistant to Stx1-induced apoptosis and Stx1 effects on chemokine expression patterns. In contrast, a population of vimentin-positive cells, i.e., mesenchymal/nonepithelial cells that had high numbers of Stx receptors on their surface, was depleted from the cultures by Stx1. In situ, CD77(+) cells were located in the lamina propria of the bovine colon by using immunofluorescence staining. A newly established vimentin-positive crypt cell line with high CD77 expression resisted the cytolethal effect of Stx1 but responded to Stx1 with a significant increase in interleukin-8 (IL-8), GRO-alpha, MCP-1, and RANTES mRNA. Combined stimulation with lipopolysaccharide and Stx1 increased IL-10 mRNA. Our results show that bovine colonic crypt cells of epithelial origin are resistant to both the cytotoxic and modulatory effects of Stx1. In contrast, some mucosal mesenchymal cells, preliminarily characterized as mucosal macrophages, are Stx1-responsive cells that may participate in the interaction of STEC with the bovine intestinal mucosa.

Cytomegalovirus blocks intestinal stroma-induced down-regulation of macrophage HIV-1 infection

Intestinal macrophages, unlike macrophages from other tissues, do not support HIV-1 infection or produce proinflammatory cytokines. In vitro studies suggest this unique, functional phenotype is a result of the exposure of newly recruited blood monocytes to intestinal stromal products. However, in AIDS-related CMV colitis, mucosal macrophages express HIV-1 and proinflammatory cytokines. Therefore, we investigated the mechanism by which CMV confers permissiveness to HIV-1 and cytokine production on intestinal macrophages. We show that intestinal stroma-conditioned media (S-CM) down-regulated monocyte-derived macrophage infection by HIV-1 (pseudotyped with YU2 envelope or vesicular stomatitis virus glycoprotein) and production of TNF-alpha, but preinfection of the cells with CMV reversed this down-regulation, enhancing HIV-1 infection, p24 production, and TNF-alpha release. The ability of CMV to reverse S-CM down-regulation of macrophage HIV-1 infection was blocked by anti-TNF-alpha antibodies and over-ridden by exogenous TNF-alpha. Immunohistochemical analysis of monocyte-derived macrophages exposed to CMV and HIV-1 (YU2 pseudotype) revealed that the cells infrequently contained CMV and HIV-1 viral proteins. In addition, analysis of colon tissue sections from HIV-1-infected patients with CMV colitis showed that some macrophage-like cells contained CMV and TNF-alpha proteins, others contained HIV-1 and TNF-alpha proteins, but cells infrequently contained CMV and HIV-1 proteins. These results indicate that CMV blocks stromal product inhibition of HIV-1 infection in macrophages, and this inhibition is mediated, at least in part, by CMV-induced TNF-alpha acting in trans to enhance HIV-1 infection.

Lactic acid bacterial colonization and human rotavirus infection influence distribution and frequencies of monocytes/macrophages and dendritic cells in neonatal gnotobiotic pigs

Despite accumulating knowledge of porcine macrophages and dendritic cells (DCs) from in vitro studies, information regarding monocytes/macrophages and DCs in lymphoid tissues of enteric pathogen-infected neonatal animals in vivo is limited. In this study we evaluated the influence of commensal bacterial [two strains of lactic acid bacteria (LAB), Lactobacillus acidophilus and L. reuteri] colonization and rotavirus infection on distribution and frequencies of monocytes/macrophages and conventional DCs (cDCs) in ileum, spleen and blood. Gnotobiotic pigs were inoculated with LAB and virulent Wa strain human rotavirus (HRV) (LAB+HRV+), HRV only (LAB−HRV+), LAB only (LAB+HRV−) or mock (LAB−HRV−). The cDCs were characterized as SWC3⁺CD11R1⁺, whereas monocytes/macrophages were identified as SWC3⁺CD11R1⁻ by flow cytometry in the gnotobiotic pigs at 10 days of age. Infection with HRV alone activated/recruited significantly more monocytes/macrophages to the intestine than LAB colonization and 56% versus 28% of these cells expressed CD14. Colonization with LAB alone also significantly increased the frequencies of monocytes/macrophages and cDCs and the CD14 expression on monocytes/macrophages in ileum and spleen compared to the controls. LAB colonization plus HRV infection significantly reduced macrophage and cDC frequencies in spleen compared to LAB colonization or HRV infection alone, suggesting that LAB colonization down-regulated HRV− infection-induced monocyte/macrophage activation/recruitment at the systemic lymphoid tissue. These results illustrated the distribution of porcine monocytes/macrophages and cDCs and the frequencies of CD14 expression on these cells in intestinal and systemic lymphoid tissues in the early stage of immune responses to intestinal colonization by LAB versus infection by an enteric pathogen HRV and will facilitate further in vivo studies on functional characterization of these immune cells in neonates.

Adaptations of intestinal macrophages to an antigen-rich environment

Intestinal macrophages, preferentially located in the subepithelial lamina propria, represent in humans the largest pool of tissue macrophages. To comply with their main task, i.e. the efficient removal of microbes and particulate matter that might have gained access to the mucosa from the intestinal lumen while maintaining local tissue homeostasis, several phenotypic and functional adaptations evolved. Most notably, microbe-associated molecular pattern (MAMP) receptors, including the lipopolysaccharide receptors CD14 and TLR4, but also the Fc receptors for IgA and IgG are absent on most intestinal Mø. Here we review recent findings on the phenotypic and functional adaptations of intestinal Mø and their implications for the pathogenesis of inflammatory bowel diseases.

Monocyte chemoattractant protein-1 (MCP-1) inhibits the intestinal-like differentiation of monocytes

Monocytes (MO) migrating into normal, non-inflamed intestinal mucosa undergo a specific differentiation resulting in a non-reactive, tolerogenic intestinal macrophage (IMAC). Recently we demonstrated the differentiation of MO into an intestinal-like macrophage (MAC) phenotype in vitro in a three-dimensional cell culture model (multi-cellular spheroid or MCS model). In the mucosa of patients with inflammatory bowel disease (IBD) in addition to normal IMAC, a reactive MAC population as well as increased levels of monocyte chemoattractant protein 1 (MCP-1) is found. The aim of this study was to investigate the influence of MCP-1 on the differentiation of MO into IMAC. MCS were generated from adenovirally transfected HT-29 cells overexpressing MCP-1, macrophage inflammatory protein 3 alpha (MIP-3alpha) or non-transfected controls and co-cultured with freshly elutriated blood MO. After 7 days of co-culture MCS were harvested, and expression of the surface antigens CD33 and CD14 as well as the intracellular MAC marker CD68 was determined by flow-cytometry or immunohistochemistry. MCP-1 and MIP-3alpha expression by HT-29 cells in the MCS was increased by transfection at the time of MCS formation. In contrast to MIP-3alpha, MCP-1 overexpression induced a massive migration of MO into the three-dimensional aggregates. Differentiation of IMAC was disturbed in MCP-1-transfected MCS compared to experiments with non-transfected control aggregates, or the MIP-3alpha-transfected MCS, as indicated by high CD14 expression of MO/IMAC cultured inside the MCP-1-transfected MCS, as shown by immunohistochemistry and FACS analysis. Neutralization of MCP-1 was followed by an almost complete absence of monocyte migration into the MCS. MCP-1 induced migration of MO into three-dimensional spheroids generated from HT-29 cells and inhibited intestinal-like differentiation of blood MO into IMAC. It may be speculated that MCP-1 could play a role in the disturbed IMAC differentiation in IBD mucosa.

A new organotypic model to study cell interactions in the intestinal mucosa

BACKGROUND

Recently, we demonstrated that freshly elutriated monocytes differentiate into macrophages with a phenotype similar to that of intestinal macrophages in a three-dimensional model of intestinal epithelial cells. Here we describe a more organotypic model to study cell interactions in the intestinal mucosa.

METHODS

Primary intestinal fibroblasts and freshly elutriated blood monocytes (ratio 1:1) were embedded in collagen type I gels and cultured for 5 days. At day 5, intestinal epithelial cells (HT-29) were seeded on top of the collagen gels. After another 7 days collagen gels were harvested and fixed for immunohistochemical analysis. Cryosections of the aggregates were prepared and staining for monocyte/macrophage markers and basement membrane compounds was performed. Cell interactions inside the aggregates were examined by electron microscopy.

RESULTS

Intestinal fibroblasts contracted the collagen gels which formed stable three-dimensional aggregates within the first 5 days of culture. Intestinal epithelial cells formed a monolayer on top of the gels about 3 days after seeding. Intestinal fibroblasts were distributed randomly over the aggregate. Monocytes inside aggregates were localized in the vicinity to epithelial cells by positive staining for CD68. Typical monocyte/macrophage specific markers such as CD14, CD16, CD11b, CD11c and the co-stimulatory molecules CD80 and CD86 were down-regulated or not detectable on these cells after co-culture in three-dimensional aggregates. Omission of epithelial cells from the model was followed by impaired differentiation of intestinal macrophages.

CONCLUSION

In the three-dimensional organotypic cell culture model monocytes differentiate into intestinal-like macrophages when co-cultured with control intestinal fibroblasts and intestinal epithelial cells. Intestinal epithelial cells may be necessary for differentiation of intestinal macrophages.

Protein tyrosine kinase and p38 MAP kinase pathways are involved in stimulation of matrix metalloproteinase-9 by TNF-alpha in human monocytes

Matrix metalloproteinase-9 (MMP-9), through its catalytic and non-catalytic activities, plays critical roles in inflammation, tumor invasion and angiogenesis. Human monocytes actively involved in inflammatory and tumoral states secrete proMMP-9 (92kDa). Endogenous TNF-alpha stimulates MMP-9 gene transcription in monocytes through NF-kappaB activation. In this study, we investigated the intracellular signaling pathways underlying TNF-alpha/NF-kappaB-dependent expression of MMP-9 in monocytes using chemical inhibitors that specifically inhibit distinct kinase pathways. We confirmed the expression of MMP-9 by reverse transcription chain reaction (RT-PCR), ELISA and gelatin zymography. PGE2/cAMP inhibitor indomethacin, PI-3K inhibitor wortmannin, PKC inhibitor bisindolylmaleimide and PKA inhibitor H-89 did not affect the levels of released MMP-9. In contrast, MMP-9 mRNA and protein expression was down-regulated by p38 MAPK inhibitor SB203580 and protein tyrosine kinase (PTK) inhibitor tyrphostin 25. These inhibitors increased IkappaB-alpha levels, which correlate with decreased NF-kappaB activation. Although SB203580 induced a decrease in TNF-alpha release, addition of exogenous TNF-alpha did not reverse the inhibitory effect of SB203580 toward MMP-9 thus suggesting that SB203580 could modulate down-stream effects of TNF-alpha. In parallel, TIMP-1 levels decreased in the presence of SB203580. Both kinase inhibitors did not influence the maturation pathway of monocytes. Our results indicate that these two inhibitors of p38 MAPK and PTK pathways could be used as combined targets for inhibiting MMP-9 expression in inflamed tissues.

Inherent potential for production of tumor necrosis factor-alpha by human intestinal macrophages

BACKGROUND AND AIMS

Tumor necrosis factor (TNF) production by the macrophages in intestines appears to play a critical role in the pathogenesis of Crohn's disease (CD). However, it is reported that resident intestinal macrophages (both colonic and small-bowel) do not produce TNF after lipopolysaccharide (LPS) stimulation. It has not yet been proven whether or not intestinal macrophages have an inherent potential to produce TNF. The purpose of this study is to answer this question.

MATERIALS AND METHODS

Colonic macrophages were isolated from lamina propria of human large intestine and stimulated with a variety of substances: LPS, a lipid A derivative (ONO-4007), killed Streptococcus bacterial body (OK-432), phorbol 12-myristate 13-acetate, and lectins (pokeweed mitogen and Sarcophaga lectin).

RESULTS

Colonic macrophages were phenotypically negative for CD14 and positive for CD68 and produced very little TNF in response to LPS, as reported previously. Of the substances tested, only Sarcophaga lectin, which is a defense protein of fleshflies (Sarcophaga peregrina), induced TNF production by the intestinal macrophages. In addition, when the colonic macrophages were cultured on immunoglobulin-A-coated dishes, their characteristic response to LPS was altered, and they produced TNF at a level 6.6 times higher than when on collagen-coated dishes.

CONCLUSION

Colonic macrophages have an inherent ability to produce TNF. Activation of colonic macrophages by unknown substances may contribute to the induction of TNF production, which causes the intestinal inflammation of CD.

Specific messenger RNA expression for signal transduction molecules by lipopolysaccharide in intestinal macrophages

Intestinal macrophages are known to display profound inflammatory anergy in response to lipopolysacchraide (LPS). To study the mechanisms of unresponsiveness of intestinal macrophages to LPS, we compared the mRNA expression of molecules associated with signal transduction of intestinal macrophages with those of other tissue macrophages. Also cellular localization of CD14 protein was examined. Intestinal, alveolar and peritoneal macrophages were isolated from rats or mice. The expression of mRNA was assessed by real-time PCR, and cellular localization of CD14 protein was examined by flow cytometry. Cellular responses to LPS were examined by production of TNF and NO. The expression of CD14 mRNA in intestinal macrophages was lower than for peritoneal macrophages but higher than for alveolar macrophages. The mRNA expression of other molecules corresponding to intracellular signal transduction in intestinal macrophages was similar with alveolar and peritoneal macrophages. Despite the presence of CD14 mRNA, proteins of CD14 were not detected on cell surfaces of intestinal macrophages, and induction of TNF or NO responding to LPS were not detected. Flow cytometric analysis demonstrated that CD14 protein was not expressed on the cell surface but was expressed inside intestinal macrophages. The unresponsiveness of intestinal macrophages after LPS exposure is considered to be largely attributed to the lack of CD14 protein on their cell surfaces. However, CD14 protein was expressed inside of the cells, suggesting that post-transcriptional regulation rather than transcriptional suppression may play a dominant role in determining the phenotype of the intestinal macrophages.

Isolation and purification of human intestinal macrophages

The gastrointestinal mucosa contained within the lamina propria is the largest reservoir of macrophages in the human body. The isolation and study of this population of cells is important for understanding host defense and the pathogenesis of inflammation in the gastrointestinal mucosa. This unit describes methods that can be used to isolate and purify intestinal macrophages. Sources of intestinal tissue that can be used for this isolation include human subjects undergoing gastrojejunostomy for obesity, organ-transplantation donors, or the noninflamed margin of resected segments of small intestine from subjects undergoing resection for surgically indicated reasons.

Intestinal macrophages: unique effector cells of the innate immune system

The gastrointestinal mucosa is the largest reservoir of macrophages in the body. These important effector cells are derived from blood monocytes that are recruited to the lamina propria by endogenous chemoattractants in the non-inflamed mucosa and by inflammatory chemokines and bacterial products during inflammation. In the non-inflamed mucosa, newly recruited pro-inflammatory monocytes are exposed to lamina propria stromal (extracellular matrix) factors that induce phenotypic and functional differentiation into non-inflammatory macrophages. As a consequence of this differentiation, resident lamina propria macrophages are strikingly downregulated for the expression of innate response receptors, such as the receptors for lipopolysaccharide, immunoglobulin G (IgG), and IgA, and the production of pro-inflammatory cytokines, including interleukin-1 (IL-1), IL-6, IL-8, and tumor necrosis factor-alpha. Despite downregulated pro-inflammatory function, strong phagocytic and bactericidal activities remain intact. Thus, in the non-inflamed intestinal mucosa, lamina propria macrophages are non-inflammatory but retain avid scavenger and host defense functions, a unique but ideal phenotype and functional profile for effector cells in close proximity to immunostimulatory microorganisms and products.

Physiological Role of Macrophage Inflammatory Protein-3α Induction during Maturation of Intestinal Macrophages

Intestinal macrophages (IMAC) are a central component in the defense of the intestinal mucosa against luminal microbes. In normal mucosa, monocytes differentiate to immunologically tolerant IMAC with a typical phenotype lacking activation markers such as CD14 and TLRs 2 and 4. CD33+ IMAC were isolated from normal intestinal mucosa by immunomagnetic beads. A subtractive hybridization subtracting mRNA from normal IMAC from those of in vitro differentiated macrophages was performed. IMAC differentiation was studied in multicellular spheroids (MCS). Functional assays on migration of CD45R0+ T cells were performed in MCS coculture models. Of 76 clones, 3 obtained by subtractive mRNA hybridization showed >99% homology to mRNA of MIP-3alpha, indicating that this chemokine is induced in IMAC compared with in vitro differentiated macrophages. MIP-3alpha protein expression was confirmed in cryostat sections of normal intestinal mucosa by immunohistochemistry. IMAC in the lamina propria stained positive for MIP-3alpha. FACS of purified IMAC clearly indicated expression of MIP-3alpha in these cells. In the MCS-in vitro differentiation model for IMAC, MIP-3alpha protein expression was absent on day 1 but detectable on day 7 of coculture, demonstrating the induction of MIP-3alpha during differentiation of IMAC. IMAC attracted CD45R0+ T cells to migrate into an MCS coculture model. In human mucosa, a close contact between IMAC and CD45R0+ T cells could be demonstrated. MIP-3alpha is induced during the differentiation of monocytes into IMAC. Our data suggest that MIP-3alpha expression could be involved in the recruitment of CD45R0+ cells into the lamina propria.

Human intestinal macrophages display profound inflammatory anergy despite avid phagocytic and bacteriocidal activity

Intestinal macrophages, which are thought to orchestrate mucosal inflammatory responses, have received little investigative attention compared with macrophages from other tissues. Here we show that human intestinal macrophages do not express innate response receptors, including the receptors for LPS (CD14), Fcalpha (CD89), Fcgamma (CD64, CD32, CD16), CR3 (CD11b/CD18), and CR4 (CD11c/CD18); the growth factor receptors IL-2 (CD25) and IL-3 (CD123); and the integrin LFA-1 (CD11a/CD18). Moreover, resident intestinal macrophages also do not produce proinflammatory cytokines, including IL-1, IL-6, IL-10, IL-12, RANTES, TGF-beta, and TNF-alpha, in response to an array of inflammatory stimuli but retain avid phagocytic and bacteriocidal activity. Thus, intestinal macrophages are markedly distinct in phenotype and function from blood monocytes, although intestinal macrophages are derived from blood monocytes. To explain this paradox, we show that intestinal stromal cell-derived products downregulate both monocyte receptor expression and, via TGF-beta, cytokine production but not phagocytic or bacteriocidal activity, eliciting the phenotype and functional profile of intestinal macrophages. These findings indicate a mechanism in which blood monocytes recruited to the intestinal mucosa retain avid scavenger and host defense functions but acquire profound "inflammatory anergy," thereby promoting the absence of inflammation characteristic of normal intestinal mucosa despite the close proximity of immunostimulatory bacteria.

Human intestinal macrophages display profound inflammatory anergy despite avid phagocytic and bacteriocidal activity

Intestinal macrophages, which are thought to orchestrate mucosal inflammatory responses, have received little investigative attention compared with macrophages from other tissues. Here we show that human intestinal macrophages do not express innate response receptors, including the receptors for LPS (CD14), Fcalpha (CD89), Fcgamma (CD64, CD32, CD16), CR3 (CD11b/CD18), and CR4 (CD11c/CD18); the growth factor receptors IL-2 (CD25) and IL-3 (CD123); and the integrin LFA-1 (CD11a/CD18). Moreover, resident intestinal macrophages also do not produce proinflammatory cytokines, including IL-1, IL-6, IL-10, IL-12, RANTES, TGF-beta, and TNF-alpha, in response to an array of inflammatory stimuli but retain avid phagocytic and bacteriocidal activity. Thus, intestinal macrophages are markedly distinct in phenotype and function from blood monocytes, although intestinal macrophages are derived from blood monocytes. To explain this paradox, we show that intestinal stromal cell-derived products downregulate both monocyte receptor expression and, via TGF-beta, cytokine production but not phagocytic or bacteriocidal activity, eliciting the phenotype and functional profile of intestinal macrophages. These findings indicate a mechanism in which blood monocytes recruited to the intestinal mucosa retain avid scavenger and host defense functions but acquire profound "inflammatory anergy," thereby promoting the absence of inflammation characteristic of normal intestinal mucosa despite the close proximity of immunostimulatory bacteria.

Activation of a Unique Population of CD8+T Cells by Intestinal Epithelial Cells

Intestinal epithelial cells may play a role in the regulation of immune responses toward luminal antigens. We show that a subset of CD8(+) T cells undergoes oligoclonal expansion in the intestinal mucosa, probably through interaction with a unique complex expressed on epithelial cells, formed by a CEA subfamily member (gp180) and CD1d. This subset, which is regulatory in vitro, may play a role in the control of intestinal immune responses toward luminal antigens. A lack of expansion of these CD8(+) regulatory T cells, probably related to the defective expression of the gp180/CD1d complex, is observed in inflammatory bowel disease.

Stimulation of peripheral blood and intestinal mucosa cells by synthetic CpG oligodeoxynucleotides

The breakdown of tolerance to autologous bacterial flora has been implicated as a major factor contributing to the initiation and perpetuation of chronic inflammation in inflammatory bowel diseases (IBD). To test whether bacterial DNA is at the origin of inflammation in IBD, we have examined the response of lamina propria (LPMC) or peripheral mononuclear cells (PBMC) and purified T cells from IBD patients and control patients to stimulations with a set of oligodeoxynucleotides (ODNs) characterized by the presence or absence of cytosine-guanosine dinucleotides (CpG) and/or 3' poly-guanosine (poly-G) extension. Furthermore we have evaluated the costimulatory activities of these ODNs on T cells activated via CD2 or CD3 pathway. We demonstrated that CpG ODNs induce higher proliferation of LPMC from inflammatory intestinal mucosa compared to healthy mucosa. We confirmed that CpG ODNs do not directly costimulate peripheral blood T cells activated by CD3 pathway. Finally, we revealed that CpG or non-CpG ODNs with 3' poly-G extension inhibit completely CD2 activation of purified PB or LP T-cells whereas only CpG ODNs without poly-G extension enhance proliferation and IFN-gamma production of PB T cells stimulated by CD2 pathway only in presence of NK and NK T cells. Our data suggest that NK T cells may be the primary target of ODNs and play a crucial role in indirect T-cell activation by ODN.