Isolation and Flow Cytometry Analysis of Intestinal Macrophages

The intestinal macrophage pool represents the largest population of macrophages present within the body. Nevertheless, flow cytometry analysis of intestinal macrophages remains challenging due to historical lack of consensus on surface markers, variations in sample preparation, and a certain capriciousness of the isolation procedure itself. Furthermore, recent studies have uncovered a hitherto unknown heterogeneity of intestinal macrophages, accompanied by a vast increase of subset-identifying surface markers. Here, the isolation procedure for intestinal tissue for flow cytometry analysis is laid out, with particular attention toward the procedures for isolated intestinal layers, and a trouble-shooting section with strategies to avoid common pitfalls and mistakes.

NOX4 promotes mucosal barrier injury in inflammatory bowel disease by mediating macrophages M1 polarization through ROS

NADPH oxidase 4 (NOX4) plays an important role in transporting electrons in the mitochondrial respiratory chain, which is also one major source of ROS. This study investigates the mechanism by which NOX4 promotes the M1 polarization of intestinal macrophages in inflammatory bowel disease (IBD) through ROS. Dextran sulfate sodium (DSS) was used to induce the inflammatory bowel disease (IBD) in wild-type (C57BL/6N, WT) and NOX4 knockout (C57BL/6N-NOX4em1cyagen, KO) mice. Body weights of mice were dynamically monitored and the disease active index (DAI) scores were assessed. H&E staining was performed to examine pathological changes, and immunohistochemical (IHC) staining was conducted to measure the expressions of TJ proteins (ZO-1, Occludin) and CD11c. Tissue ROS labeling was accomplished with ROS probe. More ucosal permeability was assessed by FITC-D. Tissue inflammatory cytokines were detected by enzyme-linked immunosorbent assay (ELISA), while the expressions of TJ proteins (ZO-1, Occludin) were measured through Western Blotting. After NOX4 inhibitor pretreatment of intestinal macrophages in vitro, polarization was induced by lipopolysaccharide (LPS) and IFN-γ, followed by determination of polarization degree. The polarized intestinal macrophages were co-cultured with Caco-2 cells, and their effect on the monolayer cell permeability was evaluated. DSS can induce the intestinal inflammation and mucosal barrier injury in mice. Besides, it can enhance the FITC-D permeability, reduce the TJ protein levels, and promote the CD11c and ROS expressions. In KO mice, intestinal inflammation was alleviated and barrier permeability was reduced. Moreover, the TJ protein levels were higher than those of WT mice, while the CD11c and ROS were down-regulated. In WT mice, the intestinal inflammation and barrier permeability could also be reduced after treatment with NOX4 inhibitor. Overexpression of NOX4 in intestinal macrophages could promote the macrophage M1 polarization while improving the barrier integrity of Caco-2 monolayer cells. NOX4 is capable of promoting M1 polarization of intestinal macrophages through ROS, thereby further aggravating the intestinal inflammation and mucosal barrier injury in IBD. NOX4 has potential as a novel therapeutic target for IBD.

Challenge for macrophages and mast cells of Chelon ramada to counter an intestinal microparasite, Myxobolus mugchelo (Myxozoa)

Thinlip mullet Chelon ramada is the most abundant mullet species found in the Comacchio lagoons (northern Adriatic Sea, Italy). Histological and ultrastructural sections of the intestine of C. ramada showed that over 83% of 48 mullets were infected with the intestinal parasite Myxobolus mugchelo (Myxozoa). In histological sections, plasmodia of M. mugchelo containing mature spores were situated closer to mucosal folds and were surrounded by numerous mast cells (MCs). Mature spores, generally oval in shape, were observed in the paracellular space among the enterocytes or within them. Near the infected epithelial cells, several MCs, rodlet cells and few neutrophils occurred. In intestinal epithelium, large cells resembling macrophages, some with spores of M. mugchelo inside, were observed. These macrophage-like cells were foamy and possessed elongate striated granules. The number of MCs and macrophages in the intestinal epithelium was significantly higher in parasitized fish. In some parasitized intestines, portions of epithelium were displaced by spores, or the spores were observed inside the damaged enterocytes. Immunohistochemical analysis of C. ramada infected or uninfected intestinal tissue revealed the presence of histamine, serotonin (5-HT), leu-enkephalin and inducible-nitric oxide synthase in epithelial macrophages. Several epithelial cells positive to proliferating cell-nuclear antigen were also observed in the proximity of the macrophages. The current study is the first to record the occurrence of intraepithelial macrophages which engulf myxozoan spores. A hypothesis on migration of spores from pancreas via intestinal wall to gut lumen is presented.

Cells of the innate and adaptive immunity and their interactions in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of chronic inflammatory conditions of the gastrointestinal tract that includes two major phenotypes, Crohn's disease and ulcerative colitis that are characterized by different clinical features and different course of the immune response. The exact aetiology of IBD still remains unknown, although it is thought that the diseases result from an excessive immune response directed against microbial or environmentally derived antigens which can be triggered by the disruption of the intestinal epithelial barrier integrity. In this review we present immune mechanisms and interactions between cells of the immune system and tissue environment that contribute to the development and progression of IBD in humans. Since dysregulation of the intestinal immune response is a hallmark of chronic inflammatory conditions, we characterize cells of the innate and adaptive immunity involved in the pathogenesis of IBD and their cross-talks. We describe various subclasses of recently discovered innate lymphoid cells, as well as dendritic cells, macrophages and T cells, including Th17, Th22 and T regulatory cells, present in the intestinal lamina propria and cytokine-mediated regulation of the immune response in IBD, highlighting the role of IL-22 and IL-17A/IL-23 axis. Insights into novel therapeutic modalities targeting certain elements of the immune pathways important for the pathogenesis of IBD have been also shortly presented.

Interspecies communication between plant and mouse gut host cells through edible plant derived exosome-like nanoparticles

SCOPE

Exosomes, small vesicles participating in intercellular communication, have been extensively studied recently; however, the role of edible plant derived exosomes in interspecies communication has not been investigated. Here, we investigate the biological effects of edible plant derived exosome-like nanoparticles (EPDENs) on mammalian cells.

METHODS AND RESULTS

In this study, exosome-like nanoparticles from four edible plants were isolated and characterized. We show that these EPDENs contain proteins, lipids, and microRNA. EPDENs are taken up by intestinal macrophages and stem cells. The results generated from EPDEN-transfected macrophages indicate that ginger EPDENs preferentially induce the expression of the antioxidation gene, heme oxygenase-1 and the anti-inflammatory cytokine, IL-10; whereas grapefruit, ginger, and carrot EPDENs promote activation of nuclear factor like (erythroid-derived 2). Furthermore, analysis of the intestines of canonical Wnt-reporter mice, i.e. B6.Cg-Tg(BAT-lacZ)3Picc/J mice, revealed that the numbers of β-galactosidase(+) (β-Gal) intestinal crypts are increased, suggesting that EPDEN treatment of mice leads to Wnt-mediated activation of the TCF4 transcription machinery in the crypts.

CONCLUSION

The data suggest a role for EPDEN-mediated interspecies communication by inducing expression of genes for anti-inflammation cytokines, antioxidation, and activation of Wnt signaling, which are crucial for maintaining intestinal homeostasis.

Effect of TREM-1 expression in intestinal macrophages on their invasion and proliferation of intestinal epithelial cells

AIM: To explore the effect of TREM-1 expression in intestinal macrophages on their invasion and proliferation of intestinal epithelial cells to clarify the possible role of intestinal macrophages in the pathogenesis of intestinal barrier dysfunction (IBD).

METHODS: The expression levels of TREM-1 and TNF-α mRNAs in intestinal macrophages were determined by real-time PCR (RT-PCR) in vitro. After intestinal macrophages were co-cultured with intestinal epithelial cells in Transwell chamber, the growth curve of intestinal epithelial cells was determined by MTT assay. The matrigel invasion assay was used to detect the invasion of intestinal macrophages.

RESULTS: The expression levels of TREM-1 and TNF-α in the LPS group were significantly increased compared with the control group and LPS + LP17 group (both P < 0.05), but showed no significant difference between the control group and LPS + LP17 group (P > 0.05). Compared to the control group, the growth of intestinal epithelial cells was inhibited in the LPS group and LPS + LP17 group (both P < 0.05), and the inhibitory effect was more significant in the LPS group (P < 0.01). The average numbers of invading cells in the three groups were 29.3 ± 2.1, 46.0 ± 3.6, and 34.7 ± 3.1, respectively. There was a statistically significant difference in the average number of invading cells between the LPS + LP17 group and LPS group (P < 0.05).

CONCLUSION: The expression of TREM-1 was inhibited by LP17 in intestinal macrophages, and TREM-1 expression inhibited the invasion of intestinal macrophages to intestinal epithelial cells. TREM-1 may be a new target for treatment of IBD.

Role of soluble factors and three-dimensional culture in in vitro differentiation of intestinal macrophages

AIM: To examine the factor(s) involved in differentiation of intestinal macrophages (IMACs) using a recently established in vitro model.

METHODS: To test whether soluble or membrane bound factors induce IMAC-differentiation, freshly elutriated monocytes (MO) were incubated with conditioned media or cell membranes of intestinal epithelial cells (IEC) or cultured with IEC in transwell systems. To determine the importance of an active migration of MO, three-dimensional aggregates from a 1:1-mixture of MO and IEC were examined by immunohistochemistry and flow cytometry. Apoptosis was examined by caspase-3 Western blots. Extracellular matrix production in differentiation models was compared by immunohistochemistry.

RESULTS: IMAC differentiation was observed in a complex three-dimensional co-culture model (multicellular spheroid, MCS) with IEC after migration of MO into the spheroids. By co-culture of MO with conditioned media or membrane preparations of IEC no IMAC differentiation was induced. Co-culture of MO with IEC in transwell-cultures, with the two cell populations separated by a membrane also did not result in intestinal-like differentiation of MO. In contrast to IEC-spheroids with immigrating MO in mixed MCS of IEC and MO only a small subpopulation of MO was able to survive the seven day culture period.

CONCLUSION: Intestinal-like differentiation of MO in vitro is only induced in the complex three-dimensional MCS model after immigration of MO indicating a role of cell-matrix and/or cell-cell interactions during the differentiation of IMACs.