Intestinal macrophages: unique effector cells of the innate immune system

Activation of aryl hydrocarbon receptor attenuates intestinal inflammation by enhancing IRF4-mediated macrophage M2 polarization

BACKGROUND

Crohn's disease (CD) is characterized by immune cell dysregulation, with macrophages playing an indisputable role. Macrophages can exhibit opposing polarization under different conditions, resulting in pro- or anti-inflammatory effects. The aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, is implicated in intestinal inflammation by regulating both innate and adaptive immune responses. However, the regulatory mechanism between AhR and macrophages in colitis has not been thoroughly investigated.

METHODS

Macrophage polarization in the colonic tissue of active CD patients was assessed. Following colitis induction in mice by 2,4,6-trinitro-benzenesulfonic acid (TNBS), an intraperitoneal injection of the natural AhR agonist 6-formylindolo[3,2-b]carbazole (FICZ) was administered. The severity of colitis was estimated, and macrophage polarization was detected. In an in vitro setting, bone marrow-derived macrophages (BMDMs) were polarized to the M2 phenotype in the presence or absence of FICZ. Interferon regulatory factor 4 (IRF4) siRNA was applied to knockdown IRF4 expression. M2-specific markers were quantified using quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

RESULTS

Compared with healthy controls, active CD patients exhibited a lower presence of M2 macrophages in colonic tissue. Experimentally, FICZ was found to protect mice against TNBS-induced colitis, as evidenced by reduced diarrhea, bloody stool, and weight loss. This effect was associated with an increase in M2 macrophages and the release of IL-10 in the intestine. In BMDMs, FICZ promoted the expressions of M2-specific markers, including Ym1, Fizz1, IL-10, and CD206. Furthermore, FICZ upregulated IRF4 expression. After IRF4 silencing with siRNA, the enhancement of macrophage M2 polarization by FICZ was significantly impaired.

CONCLUSION

Activation of AhR appears to have a beneficial effect on intestinal inflammation by promoting macrophage M2 polarization. This effect is partially mediated by the upregulation of IRF4 expression and may lead to new insight into the pathogenesis of CD.

Spleen tyrosine kinase aggravates intestinal inflammation through regulating inflammatory responses of macrophage in ulcerative colitis

BACKGROUND

Ulcerative colitis (UC) is a persistent chronic, non-specific inflammatory disease, and macrophages play a crucial role in its pathogenesis. Spleen tyrosine kinase (Syk) is strongly associated with the pathogenesis of several inflammatory diseases. However, the role of Syk in the pathogenesis of UC is still obscure.

METHODS

Syk expression was analyzed in peripheral blood mononuclear cells (PBMCs) and colonic tissues of UC patients using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunofluorescence. A public database was used to analyze the expression of selected signature genes of interest in UC patients with different expressions of Syk. R788, a small molecule inhibitor of Syk, was used to treat macrophages from mice. The functions of macrophages were assessed using qRT-PCR, flow cytometry, and fluorescence microscopy. Dextran sodium sulfate (DSS)-induced colitis mice model was established to determine the role of Syk in UC.

RESULTS

The Syk levels were markedly increased in PBMCs, colonic tissues, and colonic mucosa lamina propria macrophages from UC patients, and positively related to disease activity. Inhibition of Syk with R788 decreased pro-inflammatory genes expression and increased anti-inflammatory genes expression in peritoneal macrophages and bone marrow macrophages. Blockade of Syk enhanced phagocytosis and bactericidal ability of macrophages. Syk promoted the production of reactive oxygen species of macrophages and M1-type macrophage polarization. Furthermore, inhibition of Syk alleviated intestinal mucosal inflammation in DSS-induced colitis model.

CONCLUSIONS

Syk plays a vital role in intestinal inflammation by regulating inflammatory responses of macrophages in UC. Targeting Syk may be a promising therapeutic approach for UC.

Christensenellaceae minuta modulates epithelial healing via PI3K-AKT pathway and macrophage differentiation in the colitis

Ulcerative colitis (UC) is a chronic inflammatory disorder with an unsatisfactory cure rate and mucosal healing is a key treatment objective. Christensenellaceae minuta (C. minuta) has emerged as a next-generation of probiotic for maintaining intestinal health. We investigated the therapeutic efficacy of C. minuta in dextran sulfate sodium (DSS)-induced colitis, focusing on mucosal healing and the underlying mechanisms. C. minuta effectively alleviated colitis and promoted the regeneration of intestinal epithelial cells (IECs). Using 16S rRNA sequencing and metabolomics, we found that C. minuta administration increased beneficial bacteria, decreased pathogenic bacteria, and significantly elevated propionic acid levels. Additionally, C. minuta activated the PI3K-AKT pathway by upregulating systemic and local IGF-1 expression. Inhibiting the PI3K-AKT pathway reduced the therapeutic effects of C. minuta and impaired IEC regeneration. Furthermore, C. minuta promoted macrophage differentiation into the M2 phenotype and decreased proinflammatory factors. We propose that C. minuta alleviates colitis by regulating the gut microbiota, modulating macrophage differentiation, and enhancing mucosal healing by activating the PI3K-AKT pathway via IGF-1 secretion induced by short-chain fatty acids. Our findings provide evidence from animal experiments to support future clinical trials and the therapeutic translation of C. minuta.

Interferon inducible guanylate-binding protein 1 modulates the lipopolysaccharide-induced cytokines/chemokines and mitogen-activated protein kinases in macrophages

Guanylate-binding proteins (GBPs) are a family of interferon (IFN)-inducible GTPases and play a pivotal role in the host immune response to microbial infections. These are upregulated in immune cells after recognizing the lipopolysaccharides (LPS), the major membrane component of Gram-negative bacteria. In the present study, the expression pattern of GBP1-7 was initially mapped in phorbol 12-myristate 13-acetate-differentiated human monocytes THP-1 and mouse macrophages RAW 264.7 cell lines stimulated with LPS. A time-dependent significant expression of GBP1-7 was observed in these cells. Moreover, among the various GBPs, GBP1 has emerged as a central player in regulating innate immunity and inflammation. Therefore, to study the specific role of GBP1 in LPS-induced inflammation, knockdown of the Gbp1 gene was carried out in both cells using small interfering RNA interference. Altered levels of different cytokines (interleukin [IL]-4, IL-10, IL-12β, IFN-γ, tumor necrosis factor-α), inducible nitric oxide synthase, histocompatibility 2, class II antigen A, protein kinase R, and chemokines (chemokine (C-X-C motif) ligand 9 [CXCL9], CXCL10, and CXCL11) in GBP1 knockdown cells were reported compared to control cells. Interestingly, the extracellular-signal-regulated kinase 1/2 mitogen-activated protein (MAP) kinases and signal transducer and activator of transcription 1 (STAT1) transcription factor levels were considerably induced in knockdown cells compared to the control cells. However, no change in the level of phosphorylated nuclear factor-kB, c-Jun, and p38 transcription factors was observed in GBP1 knockdown cells compared to the control cells. This study concludes that GBP1 may alter the expression of cytokines, chemokines, and effector molecules mediated by MAP kinases and STAT1 transcription factors.

Gut Microbiome-Related Anti-Inflammatory Effects of Aryl Hydrocarbon Receptor Activation on Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is one of the most prevalent chronic inflammations of the gastrointestinal tract (GIT). The gut microbial population, the cytokine milieu, the aryl hydrocarbon receptor (AHR) expressed by immune and nonimmune cells and the intrinsic pathway of Th-cell differentiation are implicated in the immunopathology of IBD. AHR activation requires a delicate balance between regulatory and effector T-cells; loss of this balance can cause local gut microbial dysbiosis and intestinal inflammation. Thus, the study of the gut microbiome in association with AHR provides critical insights into IBD pathogenesis and interventions. This review will focus on the recent advancements to form conceptional frameworks on the benefits of AHR activation by commensal gut bacteria in IBD.

Interleukin 17 B regulates colonic myeloid cell infiltration in a mouse model of DSS-induced colitis

Cytokines play vital roles in the pathogenesis of inflammatory bowel disease. IL17B is protective in the development of colitis. However, how IL17B regulates intestinal inflammation and what cells are regulated by IL17B is still unknown. Here, we aimed to illustrate the IL17B dependent cellular and molecular changes in colon tissue in a mouse colitis model. The results showed that IL17B expression in colon tissues was elevated in inflamed tissues than non-inflamed tissues of IBD patients. Wild type (WT) and Il17b deficient (Il17b ^-/-) mice were given 2.5% dextran sodium sulfate (DSS) water, and in some case, Il17b ^-/- mice were treated with recombinant mouse IL17B. IL17B deficiency resulted in severe DSS-induced colitis with exaggerated weight loss, shorter colon length, and elevated proinflammatory cytokines in colon. Reconstitution of Il17b ^-/- mice with recombinant IL17B alleviated the severity of DSS-induced colitis. Single cell transcriptional analyses of CD45⁺ immune cells in colonic lamina propria revealed that loss of IL17B resulted in an increased neutrophil infiltration and enhanced inflammatory cytokines in intestinal macrophages in colitis, which were confirmed by real-time PCR and flow cytometry. IL17B treatment also inhibited lipopolysaccharide-induced inflammation in bone marrow-derived macrophages and mice. IL17B inhibits colitis by regulating colonic myeloid cell response. It might represent a novel potential therapeutic approach to treat the colitis.

Lactobacillus johnsonii alleviates colitis by TLR1/2-STAT3 mediated CD206+ macrophagesIL-10 activation

Imbalance of gut microbiota homeostasis is related to the occurrence of ulcerative colitis (UC), and probiotics are thought to modulate immune microenvironment and repair barrier function. Here, in order to reveal the interaction between UC and gut microbiota, we screened a new probiotic strain by 16S rRNA sequencing from Dextran Sulfate Sodium (DSS)-induced colitis mice, and explored the mechanism and clinical relevance. Lactobacillus johnsonii (L. johnsonii), as a potential anti-inflammatory bacterium was decreased colonization in colitis mice. Gavage L. johnsonii could alleviate colitis by specifically increasing the proportion of intestinal macrophages and the secretion of Il-10 with macrophages depleted model and in Il10^-/- mice. We identified this subset of immune cells activated by L. johnsonii as CD206⁺ macrophages^IL-10. Mechanistically, L. johnsonii supplementation enhanced the mobilization of CD206⁺ macrophages^IL-10 through the activation of STAT3 in vivo and in vitro. In addition, we revealed that TLR1/2 was essential for the activation of STAT3 and the recognition of L. johnsonii by macrophages. Clinically, there was positive correlation between the abundance of L. johnsonii and the expression level of MRC1, IL10 and TLR1/2 in UC tissues. L. johnsonii could activate native macrophages into CD206⁺ macrophages and release IL-10 through TLR1/2-STAT3 pathway to relieve experimental colitis. L. johnsonii may serve as an immunomodulator and anti-inflammatory therapeutic target for UC.

Lacticaseibacillus casei Strain Shirota Modulates Macrophage-Intestinal Epithelial Cell Co-Culture Barrier Integrity, Bacterial Sensing and Inflammatory Cytokines

Probiotic bacteria modulate macrophage immune inflammatory responses, with functional cytokine responses determined by macrophage subset polarisation, stimulation and probiotic strain. Mucosal macrophages exhibit subset functional heterogeneity but are organised in a 3-dimensional tissue, over-laid by barrier epithelial cells. This study aimed to investigate the effects of the probiotic Lacticaseibacillus casei strain Shirota (LcS) on macrophage-epithelial cell cytokine responses, pattern recognition receptor (PRR) expression and LPS responses and the impacts on barrier integrity. THP-1-derived M1 and M2 subset macrophages were co-cultured in a transwell system with differentiated Caco-2 epithelial cells in the presence or absence of enteropathogenic LPS. Both Caco-2 cells in monoculture and macrophage co-culture were assayed for cytokines, PRR expression and barrier integrity (TEER and ZO-1) by RT-PCR, ELISA, IHC and electrical resistance. Caco-2 monocultures expressed distinct cytokine profiles (IL-6, IL-8, TNFα, endogenous IL-10), PRRs and barrier integrity, determined by inflammatory context (TNFα or IL-1β). In co-culture, LcS rescued ZO-1 and TEER in M2/Caco-2, but not M1/Caco-2. LcS suppressed TLR2, TLR4, MD2 expression in both co-cultures and differentially regulated NOD2, TLR9, Tollip and cytokine secretion. In conclusion, LcS selectively modulates epithelial barrier integrity, pathogen sensing and inflammatory cytokine profile; determined by macrophage subset and activation status.

Ethnobotanical Uses, Phytochemistry, Toxicology, and Pharmacological Properties of Euphorbia neriifolia Linn. against Infectious Diseases: A Comprehensive Review

Medicinal plants have considerable potential as antimicrobial agents due to the presence of secondary metabolites. This comprehensive overview aims to summarize the classification, morphology, and ethnobotanical uses of Euphorbia neriifolia L. and its derived phytochemicals with the recent updates on the pharmacological properties against emerging infectious diseases, mainly focusing on bacterial, viral, fungal, and parasitic infections. The data were collected from electronic databases, including Google Scholar, PubMed, Semantic Scholar, ScienceDirect, and SpringerLink by utilizing several keywords like 'Euphorbia neriifolia', 'phytoconstituents', 'traditional uses', 'ethnopharmacological uses', 'infectious diseases', 'molecular mechanisms', 'COVID-19', 'bacterial infection', 'viral infection', etc. The results related to the antimicrobial actions of these plant extracts and their derived phytochemicals were carefully reviewed and summarized. Euphol, monohydroxy triterpene, nerifoliol, taraxerol, β-amyrin, glut-5-(10)-en-1-one, neriifolione, and cycloartenol are the leading secondary metabolites reported in phytochemical investigations. These chemicals have been shown to possess a wide spectrum of biological functions. Different extracts of E. neriifolia exerted antimicrobial activities against various pathogens to different extents. Moreover, major phytoconstituents present in this plant, such as quercetin, rutin, friedelin, taraxerol, epitaraxerol, taraxeryl acetate, 3β-friedelanol, 3β-acetoxy friedelane, 3β-simiarenol, afzelin, 24-methylene cycloarenol, ingenol triacetate, and β-amyrin, showed significant antimicrobial activities against various pathogens that are responsible for emerging infectious diseases. This plant and the phytoconstituents, such as flavonoids, monoterpenoids, diterpenoids, triterpenoids, and alkaloids, have been found to have significant antimicrobial properties. The current evidence suggests that they might be used as leads in the development of more effective drugs to treat emerging infectious diseases, including the 2019 coronavirus disease (COVID-19).

The Connection Between Rap1 and Talin1 in the Activation of Integrins in Blood Cells

Integrins regulate the adhesion and migration of blood cells to ensure the proper positioning of these cells in the environment. Integrins detect physical and chemical stimuli in the extracellular matrix and regulate signaling pathways in blood cells that mediate their functions. Integrins are usually in a resting state in blood cells until agonist stimulation results in a high-affinity conformation ("integrin activation"), which is central to integrins' contribution to blood cells' trafficking and functions. In this review, we summarize the mechanisms of integrin activation in blood cells with a focus on recent advances understanding of mechanisms whereby Rap1 regulates talin1-integrin interaction to trigger integrin activation in lymphocytes, platelets, and neutrophils.

Immunology of Inflammatory Bowel Disease: Molecular Mechanisms and Therapeutics

As a main digestive organ and an important immune organ, the intestine plays a vital role in resisting the invasion of potential pathogens into the body. Intestinal immune dysfunction remains important pathogenesis of inflammatory bowel disease (IBD). In this review, we explained the interactions among symbiotic flora, intestinal epithelial cells, and the immune system, clarified the operating mechanism of the intestinal immune system, and highlighted the immunological pathogenesis of IBD, with a focus on the development of immunotherapy for IBD. In addition, intestinal fibrosis is a significant complication in patients with long-term IBD, and we reviewed the immunological pathogenesis involved in the development of intestinal fibrogenesis and provided novel antifibrotic immunotherapies for IBD.

HG-9-91-01 Attenuates Murine Experimental Colitis by Promoting Interleukin-10 Production in Colonic Macrophages Through the SIK/CRTC3 Pathway

BACKGROUND

Interleukin-10 (IL-10) is a potent immunoregulatory cytokine that plays a pivotal role in maintaining mucosal immune homeostasis. As a novel synthetic inhibitor of salt-inducible kinases (SIKs), HG-9-91-01 can effectively enhance IL-10 secretion at the cellular level, but its in vivo immunoregulatory effects remain unclear. In this study, we investigated the effects and underlying mechanism of HG-9-91-01 in murine colitis models.

METHODS

The anti-inflammatory effects of HG-9-91-01 were evaluated on 2, 4, 6-trinitrobenzene sulfonic acid (TNBS)-, dextran sulfate sodium-induced colitis mice, and IL-10 knockout chronic colitis mice. The in vivo effector cell of HG-9-91-01 was identified by fluorescence-activated cell sorting and quantitative real-time polymerase chain reaction. The underlying mechanism of HG-9-91-01 was investigated via overexpressing SIKs in ANA-1 macrophages and TNBS colitis mice.

RESULTS

Treatment with HG-9-91-01 showed favorable anticolitis effects in both TNBS- and DSS-treated mice through significantly promoting IL-10 expression in colonic macrophages but failed to protect against IL-10 KO murine colitis. Further study indicated that HG-9-91-01 markedly enhanced the nuclear level of cAMP response element-binding protein (CREB)-regulated transcription coactivator 3 (CRTC3), whereas treatment with lentiviruses encoding SIK protein markedly decreased the nuclear CRTC3 level in HG-9-91-01-treated ANA-1 macrophages. In addition, intracolonic administration with lentiviruses encoding SIK protein significantly decreased the nuclear CRTC3 level in the lamina propria mononuclear cells and ended the anti-inflammatory activities of HG-9-91-01.

CONCLUSIONS

We found that HG-9-91-01 promoted the IL-10 expression of colonic macrophages and exhibited its anticolitis activity through the SIK/CRTC3 axis, and thus it may represent a promising strategy for inflammatory bowel disease therapy.

PKCδ/MAPKs and NF-κB Pathways are Involved in the Regulation of Ingenane-Type Diterpenoids from Euphorbia neriifolia on Macrophage Function

PURPOSE

Euphorbia neriifolia Linn. has important medicinal value in the treatment of ulcers, tumors, inflammation, chronic respiratory troubles, and so on. Although many ingredients with anti-inflammatory activity have been discovered and isolated from the Euphorbia neriifolia, the current research still cannot explain its multivariate effects on the immune response. This article aims to introduce two Ingenane-type diterpenoids from Euphorbia neriifolia with macrophage regulatory effects and to investigate the mechanism of their action.

METHODS

The stem bark of E. neriifolia was extracted with various separation methods to obtain ingenane-type diterpenoids. The RAW264.7 cells were treated with lipopolysaccharide (LPS, 1 μg/mL) to establish an inflammatory cell model. The cell viability was detected by MTT assay. The secretion of PGE2, TNF-α, IL-1β, and IL-6 was tested with ELISA. The levels of iNOS, COX-2, IκBα, JNK, ERK, p38, p-IκBα, p-JNK, p-ERK, and p-p38 in cells were detected by Western blotting. The translocation of nuclear factor-kappa B (NF-κB)/p65 subunit were evaluated by Immunofluorescence staining.

RESULTS

Ingenane-type diterpenoids, eurifoloid A (Euri A) and a new compound euphorneroid E (Euph E), were isolated from the EtOAc fraction of E. neriifolia stem bark extracts. Euph E and Euri A exhibited significant inhibition on the levels of pro-inflammatory mediators NO, IL-1β, IL-6, and iNOS on LPS-induced macrophage RAW264.7. Cellular signaling pathway studies showed that they prevented the degradation of IκBα and the translocation of NF-κB/p65 subunit. Furthermore, the production of PGE2, TNFα, and COX-2 was dramatically increased under the influence of the compounds, which were closely related to the phosphorylation of protein kinase C δ (PKCδ) and activation of mitogen-activated protein kinase (MAPKs) signaling pathway.

CONCLUSION

These results demonstrated that Euph E and Euri A exhibited multidirectional regulation on cytokines and immune function of macrophages, in addition to a good anti-inflammatory activity, and which was closely related to the regulation of PKCδ/MAPKs and NF-κB signal pathways.

Distinct integrin activation pathways for effector and regulatory T cell trafficking and function

Integrin activation mediates lymphocyte trafficking and immune functions. Conventional T cell (Tconv cell) integrin activation requires Rap1-interacting adaptor molecule (RIAM). Here, we report that Apbb1ip-/- (RIAM-null) mice are protected from spontaneous colitis due to IL-10 deficiency, a model of inflammatory bowel disease (IBD). Protection is ascribable to reduced accumulation and homing of Tconv cells in gut-associated lymphoid tissue (GALT). Surprisingly, there are abundant RIAM-null regulatory T cells (T reg cells) in the GALT. RIAM-null T reg cells exhibit normal homing to GALT and lymph nodes due to preserved activation of integrins αLβ2, α4β1, and α4β7. Similar to Tconv cells, T reg cell integrin activation and immune function require Rap1; however, lamellipodin (Raph1), a RIAM paralogue, compensates for RIAM deficiency. Thus, in contrast to Tconv cells, RIAM is dispensable for T reg cell integrin activation and suppressive function. In consequence, inhibition of RIAM can inhibit spontaneous Tconv cell-mediated autoimmune colitis while preserving T reg cell trafficking and function.

Single-Cell Transcriptomics Reveals That Metabolites Produced by Paenibacillus bovis sp. nov. BD3526 Ameliorate Type 2 Diabetes in GK Rats by Downregulating the Inflammatory Response

Chronic low-grade inflammation is widely involved in the development and progression of metabolic syndrome, which can lead to type 2 diabetes mellitus (T2DM). Dysregulation of proinflammatory and anti-inflammatory cytokines not only impairs insulin secretion by pancreatic β-cells but also results in systemic complications in late diabetes. In our previous work, metabolites produced by Paenibacillus bovis sp. nov. BD3526, which were isolated from Tibetan yak milk, demonstrated antidiabetic effects in Goto–Kakizaki (GK) rats. In this work, we used single-cell RNA sequencing (scRNA-seq) to further explore the impact of BD3526 metabolites on the intestinal cell composition of GK rats. Oral administration of the metabolites significantly reduced the number of adipocytes in the colon tissue of GK rats. In addition, cluster analysis of immune cells confirmed that the metabolites reduced the expression of interleukin (IL)-1β in macrophages in the colon and increased the numbers of dendritic cells (DCs) and regulatory T (T_reg) cells. Further mechanistic studies of DCs confirmed that activation of the WNT/β-catenin pathway in DCs promoted the expression of IL-10 and transforming growth factor (TGF)-β, thereby increasing the number of T_reg cells.

Salicylates Ameliorate Intestinal Inflammation by Activating Macrophage AMPK

BACKGROUND

Inflammatory bowel diseases are the most common chronic intestinal inflammatory conditions, and their incidence has shown a dramatic increase in recent decades. Limited efficacy and questionable safety profiles with existing therapies suggest the need for better targeting of therapeutic strategies. Adenosine monophosphate-activated protein kinase (AMPK) is a key regulator of cellular metabolism and has been implicated in intestinal inflammation. Macrophages execute an important role in the generation of intestinal inflammation. Impaired AMPK in macrophages has been shown to be associated with higher production of proinflammatory cytokines; however, the role of macrophage AMPK in intestinal inflammation and the mechanism by which it regulates inflammation remain to be determined. In this study, we investigated the role of AMPK with a specific focus on macrophages in the pathogenesis of intestinal inflammation.

METHODS

A dextran sodium sulfate-induced colitis model was used to assess the disease activity index, histological scores, macroscopic scores, and myeloperoxidase level. Proinflammatory cytokines such as tumor necrosis factor-α, interleukin-6, and interleukin-1β were measured by enzyme-linked immunosorbent assay. Transient transfection of AMPKβ1 and LC3-II siRNA in RAW 264.7 cells was performed to elucidate the regulation of autophagy by AMPK. The expression of p-AMPK, AMPK, and autophagy markers (eg, LC3-II, p62, Beclin-1, and Atg-12) was analyzed by Western blot.

RESULTS

Genetic deletion of AMPKβ1 in macrophages upregulated the production of proinflammatory cytokines, aggravated the severity of dextran sodium sulfate-induced colitis in mice, which was associated with an increased nuclear translocation of nuclear factor-κB, and impaired autophagy both in vitro and in vivo. Notably, the commonly used anti-inflammatory 5-aminosalicylic acid (ie, mesalazine) and sodium salicylate ameliorated dextran sodium sulfate-induced colitis through the activation of macrophage AMPK targeting the β1 subunit.

CONCLUSIONS

Together, these data suggest that the development of therapeutic agents targeting AMPKβ1 may be effective in the treatment of intestinal inflammatory conditions including inflammatory bowel disease.

The impact of metabolites derived from the gut microbiota on immune regulation and diseases

The gut microbiota strongly impacts the physiology and pathology in the host. To understand the complex interactions between host and gut microbiota, an 'integrated omics' approach has been employed, where exhaustive analyses for the different layers of cellular functions, such as epigenomics, transcriptomics and metabolomics, in addition to metagenomics, are combined. With this approach, the mechanisms whereby short-chain fatty acids (SCFAs) regulate host defense and the immune system have been elucidated. In a gnotobiotic mouse model of enterohemorrhagic Escherichia coli infection, Bifidobacterium-derived acetate can protect from infection-mediated death by changing the gene expression profile of colonic epithelial cells. It has also been shown that gut microbiota-derived butyrate enhances colonic regulatory T-cell differentiation through its epigenetic modulatory ability via histone deacetylase inhibition. SCFAs are involved in many other immunomodulatory effects as well as host pathophysiological conditions. Dysbiosis in the gut has been implicated in the pathogenesis of many diseases. Although the causal relationship of gut microbial dysbiosis and/or metabolites with pathogenesis is mostly unknown, mechanistic insights have been elucidated in some cases. Metabolism in the gut microbiota and host liver produces trimethylamine N-oxide, which is known to aggravate atherosclerosis, and a secondary bile acid deoxycholate, which reportedly induces non-alcoholic steatohepatitis-related hepatocellular carcinoma. It has been reported that secondary bile acids could also induce the differentiation of peripherally derived regulatory T cells in the gut. Further studies on the interactions between the host and gut microbiota could lead to the development of new therapeutic strategies as well as in preventive medicine.

A mutation that blocks integrin α4β7 activation prevents adaptive immune-mediated colitis without increasing susceptibility to innate colitis

Background

β₇ integrins are responsible for the efficient recruitment of lymphocytes from the blood and their retention in gut-associated lymphoid tissues. Integrin α₄β₇ binds MAdCAM-1, mediating rolling adhesion of lymphocytes on blood vessel walls when inactive and firm adhesion when activated, thereby controlling two critical steps of lymphocyte homing to the gut. By contrast, integrin α_Eβ₇ mediates the adhesion of lymphocytes to gut epithelial cells by interacting with E-cadherin. Integrin β₇ blocking antibodies have shown efficacy in clinical management of inflammatory bowel disease (IBD); however, fully blocking β₇ function leads to the depletion of colonic regulatory T (Treg) cells and exacerbates dextran sulfate sodium (DSS)-induced colitis by evoking aberrant innate immunity, implying its potential adverse effect for IBD management. Thus, a better therapeutic strategy targeting integrin β₇ is required to avoid this adverse effect.

Results

Herein, we inhibited integrin α₄β₇ activation in vivo by creating mice that carry in their integrin β₇ gene a mutation (F185A) which from structural studies is known to lock α₄β₇ in its resting state. Lymphocytes from β₇-F185A knock-in (KI) mice expressed α₄β₇ integrins that could not be activated by chemokines and showed significantly impaired homing to the gut. The β₇-F185A mutation did not inhibit α_Eβ₇ activation, but led to the depletion of α_Eβ₇⁺ lymphocytes in the spleen and a significantly reduced population of α_Eβ₇⁺ lymphocytes in the gut of KI mice. β₇-F185A KI mice were resistant to T cell transfer-induced chronic colitis, but did not show an increased susceptibility to DSS-induced innate colitis, the adverse effect of fully blocking β₇ function.

Conclusions

Our findings demonstrate that specific inhibition of integrin α₄β₇ activation is a potentially better strategy than fully blocking α₄β₇ function for IBD treatment.

In-Vitro Cell Culture for Efficient Assessment of Mycotoxin Exposure, Toxicity and Risk Mitigation

Mycotoxins are toxic secondary fungal metabolites that commonly contaminate crops and food by-products and thus, animal feed. Ingestion of mycotoxins can lead to mycotoxicosis in both animals and humans, and at subclinical concentrations may affect animal production and adulterate feed and animal by-products. Mycotoxicity mechanisms of action (MOA) are largely unknown, and co-contamination, which is often the case, raises the likelihood of mycotoxin interactions. Mitigation strategies for reducing the risk of mycotoxicity are diverse and may not necessarily provide protection against all mycotoxins. These factors, as well as the species-specific risk of toxicity, collectively make an assessment of exposure, toxicity, and risk mitigation very challenging and costly; thus, in-vitro cell culture models provide a useful tool for their initial assessment. Since ingestion is the most common route of mycotoxin exposure, the intestinal epithelial barrier comprised of epithelial cells (IECs) and immune cells such as macrophages, represents ground zero where mycotoxins are absorbed, biotransformed, and elicit toxicity. This article aims to review different in-vitro IEC or co-culture models that can be used for assessing mycotoxin exposure, toxicity, and risk mitigation, and their suitability and limitations for the safety assessment of animal foods and food by-products.

Role of Heparanase in Macrophage Activation

Macrophages represent one of the most diverse immunocyte populations, constantly shifting between various phenotypes/functional states. In addition to execution of vital functions in normal physiological conditions, macrophages represent a key contributing factor in the pathogenesis of some of the most challenging diseases, such as chronic inflammatory disorders, diabetes and its complications, and cancer. Macrophage polarization studies focus primarily on cytokine-mediated mechanisms. However, to explore the full spectrum of macrophage action, additional, non-cytokine pathways responsible for altering macrophage phenotype have to be taken into consideration as well. Heparanase, the only known mammalian endoglycosidase that cleaves heparan sulfate glycosaminoglycans, has been shown to contribute to the altered macrophage phenotypes in vitro and in numerous animal models of inflammatory conditions, occurring either in the presence of microbial products or in the setting of non-infectious "aseptic" inflammation. Here we discuss the involvement of heparanase in shaping macrophage responses and provide information that may help to establish the rationale for heparanase-targeting interventions aimed at preventing abnormal macrophage activation in various disorders.

A Comprehensive Review and Update on the Pathogenesis of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic and life-threating inflammatory disease of gastroenteric tissue characterized by episodes of intestinal inflammation. The pathogenesis of IBD is complex. Recent studies have greatly improved our knowledge of the pathophysiology of IBD, leading to great advances in the treatment as well as diagnosis of IBD. In this review, we have systemically reviewed the pathogenesis of IBD and highlighted recent advances in host genetic factors, gut microbiota, and environmental factors and, especially, in abnormal innate and adaptive immune responses and their interactions, which may hold the keys to identify novel predictive or prognostic biomarkers and develop new therapies.

In vitro assessment of immunomodulatory and anti-Campylobacter activities of probiotic lactobacilli

The present study was undertaken to assess the antimicrobial activity of Lactobacillus spp. (L. salivarius, L. johnsonii, L. reuteri, L. crispatus, and L. gasseri) against Campylobacter jejuni as well as their immunomodulatory capabilities. The results demonstrated that lactobacilli exhibit differential antagonistic effects against C. jejuni and vary in their ability to elicit innate responses in chicken macrophages. All lactobacilli exerted inhibitory effects on C. jejuni growth, abrogated the production of the quorum sensing molecule autoinducer-2 (AI-2) by C. jejuni and inhibited the invasion of C. jejuni in human intestinal epithelial cells. Additionally, all lactobacilli, except L. reuteri, significantly reduced the expression of virulence-related genes in C. jejuni, including genes responsible for motility (flaA, flaB, and flhA), invasion (ciaB), and AI-2 production (luxS). All lactobacilli enhanced C. jejuni phagocytosis by macrophages and increased the expression of interferon (IFN)-γ, interleukin (IL)-1β, IL-12p40, IL-10, and chemokine (CXCLi2) in macrophages. Furthermore, L. salivarius, L. reuteri, L. crispatus, and a mixture of all lactobacilli significantly increased expression of the co-stimulatory molecules CD40, CD80, and CD86 in macrophages. In conclusion, these findings demonstrate that lactobacilli possess anti-Campylobacter and immunomodulatory activities. Further studies are needed to assess their protective efficacy against intestinal colonization by C. jejuni in broiler chickens.

Human gingiva-derived mesenchymal stem cells alleviate inflammatory bowel disease via IL-10 signalling-dependent modulation of immune cells

Current evidence indicates that inflammatory bowel disease (IBD) is caused primarily by impaired mucosal immunity, resulting in an imbalance between epithelial barrier function and tissue inflammation. Human gingiva-derived mesenchymal stem cells (GMSCs) exhibit immunomodulatory and anti-inflammatory effects in a variety of immunity- and inflammation-associated diseases. However, the role of GMSCs in treating IBD has not been elucidated. Our study, therefore, examined the therapeutic effect and mechanism of GMSCs in a murine colitis model of IBD. Our results indicate that the infusion of GMSCs significantly prolonged survival and relieved symptoms. Phenotype analyses showed that the frequencies of NK1.1⁺ and CD11b⁺ cells, as well as CD4 T cells in the spleen, were suppressed in GMSC-treated mice compared with the PBS- or fibroblast-treated control groups. Additionally, GMSC treatment markedly increased the numbers of interleukin (IL)-10⁺ regulatory T cells, reduced the secretion of pro-inflammatory cytokines, and increased production of anti-inflammatory cytokines. A mechanistic study revealed that anti-IL-10R antibody abolished the protective effect of GMSCs compared with mice treated with anti-IgG antibody. Thus, our results indicate that GMSCs play a critical role in alleviating colitis by modulating inflammatory immune cells via IL-10 signalling.

Development of a Novel Ex-vivo 3D Model to Screen Amoebicidal Activity on Infected Tissue

Amoebiasis is a parasitic disease that causes thousands of deaths every year, its adverse effects and resistance to conventional treatments have led to the search of new treatment options, as well as the development of novel screening methods. In this work, we implemented a 3D model of intestine and liver slices from hamsters that were infected ex vivo with virulent E. histolytica trophozoites. Results show preserved histology in both uninfected tissues as well as ulcerations, destruction of the epithelial cells, and inflammatory reaction in intestine slices and formation of micro abscesses, and the presence of amoebae in the sinusoidal spaces and in the interior of central veins in liver slices. The three chemically synthetized compounds T-001, T-011, and T-016, which act as amoebicides in vitro, were active in both infected tissues, as they decreased the number of trophozoites, and provoked death by disintegration of the amoeba, similar to metronidazole. However, compound T-011 induced signs of cytotoxicity to liver slices. Our results suggest that ex vivo cultures of precision-cut intestinal and liver slices represent a reliable 3D approach to evaluate novel amoebicidal compounds, and to simultaneously detect their toxicity, while reducing the number of experimental animals commonly required by other model systems.

Mechanisms of Disease: Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs), represented by Crohn disease and ulcerative colitis, are associated with major morbidity in Western countries and with increasing incidence in the developing world. Although analysis of the genome of patients with IBD, especially through genome-wide association studies, has unraveled multiple pathways involved in IBD pathogenesis, only part of IBD heritability has been explained by genetic studies. This finding has revealed that environmental factors also play a major role in promoting intestinal inflammation, mostly through their effects in the composition of the microbiome. However, in order for microbial dysbiosis to result in uncontrolled intestinal inflammation, the intestinal barrier formed by intestinal epithelial cells and the innate immune system should also be compromised. Finally, activation of the immune system depends on the working balance between effector and regulatory cells present in the intestinal mucosa, which have also been found to be dysregulated in this patient population. Therefore, IBD pathogenesis is a result of the interplay of genetic susceptibility and environmental impact on the microbiome that through a weakened intestinal barrier will lead to inappropriate intestinal immune activation. In this article, we will review the mechanisms proposed to cause IBD from the genetic, environmental, intestinal barrier, and immunologic perspectives.

The bacterial siderophore enterobactin confers survival advantage to Salmonella in macrophages

Enterobactin (Ent), a prototypical bacterial siderophore known for its unparalleled affinity for iron, is widely conserved among members of the Enterobacteriaceae family of Gram-negative bacteria. In this study, we demonstrated that, aside from mediating iron acquisition, Ent also dampened the macrophages (MΦs) antimicrobial responses against intracellular infection by Salmonella enterica serovar Typhimurium. Accordingly, the loss of Ent expression (ΔentB) in Salmonella demoted their survivability against MΦs. Addition of exogenous Ent not only rescued the survival of ΔentB Salmonella, but also augmented WT Salmonella to better withstand the microbicidal activity of MΦs. The protection conferred to WT Salmonella was observed only when Ent was administered as iron-free, thus indicating the requirement of iron chelation in this context. In contrast, the exogenous iron-bound Ent retained its ability to promote the survival of ΔentB Salmonella, albeit modestly. Assessment on MΦs labile iron pool (LIP) revealed that iron-free Ent is able to permeate into MΦs, chelate the intracellular LIP, and regulate the expression of several key iron-regulatory proteins, i.e., divalent metal transporter 1, ferroportin, and hepcidin. Chelation of iron by Ent was also observed to promote the MΦs towards M2 polarization. Collectively, our findings demonstrated that Ent not only facilitates bacterial iron uptake but also disrupts MΦs iron homeostasis and M1/M2 polarization to safeguard intracellular bacteria against the anti-bacterial effects of their host.

The mycotoxin alternariol suppresses lipopolysaccharide-induced inflammation in THP-1 derived macrophages targeting the NF-κB signalling pathway

Alternariol (AOH) is a secondary metabolite formed by black mold of the genus Alternaria alternata. Due to limited hazard and occurrence data, AOH is still considered as an “emerging mycotoxin” and, as such, not monitored and regulated yet. Recent studies indicate immunosuppressive effects in vitro by altering the expression of CD molecules and proinflammatory cytokines, which are indispensable in mounting an innate immune response. However, the mode of action by which AOH exerts its immunosuppressive effects has not been unraveled yet. The present study aimed to characterise the impact of AOH on the nuclear factor kappa B (NF-κB) pathway, the expression of NF-κB target cytokines and involved regulatory microRNAs (miRNAs). In THP-1 derived macrophages, AOH (1–20 µM) was found to suppress lipopolysaccharide (LPS)-induced NF-κB pathway activation, decrease secretion of the proinflammatory cytokines IL-8, IL-6, TNF-α and to induce secretion of the anti-inflammatory IL-10. Thereby, a distinct pattern of cytokine mRNA levels was monitored, varying between short- and long-term exposure. Concomitantly, AOH (2–20 µM) affected the transcription levels of miR-146a and miR-155 in LPS-stimulated THP-1 derived macrophages dose-dependently by down- and upregulation, respectively. In contrast, transcription of miR-16 and miR-125b, two other immune-related miRNAs, was not modulated. In the absence of a LPS stimulus, AOH (20 µM) did not affect basal NF-κB activity, but increased IL-10 transcription. Collectively, our results indicate, that AOH itself does not induce a proinflammatory immune response in human macrophages; however, in an inflamed environment it possesses the ability to repress inflammation by targeting the NF-κB signalling pathway and regulatory miRNAs.

Gelatin versus its two major degradation products, prolyl-hydroxyproline and glycine, as supportive therapy in experimental colitis in mice

Gelatin is an anti-inflammatory dietary component, and its predominant metabolites entering circulation are prolyl-hydroxyproline (Pro-Hyp) and glycine. We evaluated the protective effects of orally administered gelatin, glycine, and Pro-Hyp 10:3:0.8 (w/w/w) against dextran sodium sulfate (DSS)-induced colitis in mice. According to clinical, histological, and biochemical parameters, they exhibited significant activities in the order of gelatin < glycine < Pro-Hyp. Gelatin prevented the DSS-induced increase in interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the colon, rather than in peripheral blood. Glycine and Pro-Hyp attenuated the DSS-induced rise in colonic IL-6 and TNF-α, as well as peripheral IL-1β, IL-6, and TNF-α. Hematologic results show the attenuation of DSS-induced leukocytosis and lymphocytosis by glycine and Pro-Hyp, rather than gelatin. These findings suggest that glycine and Pro-Hyp constitute the material basis for gelatin's anticolitis efficacy, and they have better anticolitis activities and distinct mechanisms of action when ingested as free compounds than as part of gelatin.

Extracellular Vesicles From the Helminth Fasciola hepatica Prevent DSS-Induced Acute Ulcerative Colitis in a T-Lymphocyte Independent Mode

The complexity of the pathogenesis of inflammatory bowel disease (ulcerative colitis and Crohn's disease) has led to the quest of empirically drug therapies, combining immunosuppressant agents, biological therapy and modulators of the microbiota. Helminth parasites have been proposed as an alternative treatment of these diseases based on the hygiene hypothesis, but ethical and medical problems arise. Recent reports have proved the utility of parasite materials, mainly excretory/secretory products as therapeutic agents. The identification of extracellular vesicles on those secreted products opens a new field of investigation, since they exert potent immunomodulating effects. To assess the effect of extracellular vesicles produced by helminth parasites to treat ulcerative colitis, we have analyzed whether extracellular vesicles produced by the parasitic helminth Fasciola hepatica can prevent colitis induced by chemical agents in a mouse model. Adult parasites were cultured in vitro and secreted extracellular vesicles were purified and used for immunizing both wild type C57BL/6 and RAG1^-/- mice. Control and immunized mice groups were treated with dextran sulfate sodium 7 days after last immunization to promote experimental colitis. The severity of colitis was assessed by disease activity index and histopathological scores. Mucosal cytokine expression was evaluated by ELISA. The activation of NF-kB, COX-2, and MAPK were evaluated by immunoblotting. Administration of extracellular vesicles from F. hepatica ameliorates the pathological symptoms reducing the amount of pro-inflammatory cytokines and interfering with both MAPK and NF-kB pathways. Interestingly, the observed effects do not seem to be mediated by T-cells. Our results indicate that extracellular vesicles from parasitic helminths can modulate immune responses in dextran sulfate sodium (DSS)-induced colitis, exerting a protective effect that should be mediated by other cells distinct from B- and T-lymphocytes.

Transmission of integrin β7 transmembrane domain topology enables gut lymphoid tissue development

Sun et al. establish the importance of transmission of changes in β-integrin transmembrane domain (TMD) topology in physiological integrin affinity modulation and biological function. Introduction of a flexible kink in the β7 integrin TMD blocks talin-mediated agonist-induced α4β7 integrin activation and function in gut lymphoid tissue development.

Integrin activation regulates adhesion, extracellular matrix assembly, and cell migration, thereby playing an indispensable role in development and in many pathological processes. A proline mutation in the central integrin β3 transmembrane domain (TMD) creates a flexible kink that uncouples the topology of the inner half of the TMD from the outer half. In this study, using leukocyte integrin α4β7, which enables development of gut-associated lymphoid tissue (GALT), we examined the biological effect of such a proline mutation and report that it impairs agonist-induced talin-mediated activation of integrin α4β7, thereby inhibiting rolling lymphocyte arrest, a key step in transmigration. Furthermore, the α4β7(L721P) mutation blocks lymphocyte homing to and development of the GALT. These studies show that impairing the ability of an integrin β TMD to transmit talin-induced TMD topology inhibits agonist-induced physiological integrin activation and biological function in development.

Adherent-invasive Escherichia coli in inflammatory bowel disease

Intestinal microbiome dysbiosis has been consistently described in patients with IBD. In the last decades, Escherichia coli, and the adherent-invasive E coli (AIEC) pathotype in particular, has been implicated in the pathogenesis of IBD. Since the discovery of AIEC, two decades ago, progress has been made in unravelling these bacteria characteristics and its interaction with the gut immune system. The mechanisms of adhesion of AIEC to intestinal epithelial cells (via FimH and cell adhesion molecule 6) and its ability to escape autophagy when inside macrophages are reviewed here. We also explore the existing data on the prevalence of AIEC in patients with Crohn's disease and UC, and the association between the presence of AIEC and disease location, activity and postoperative recurrence. Finally, we highlight potential therapeutic strategies targeting AIEC colonisation of gut mucosa, including the use of phage therapy, bacteriocins and antiadhesive molecules. These strategies may open new avenues for the prevention and treatment of IBD in the future.

Gp96 deficiency affects TLR4 functionality and impairs ERK and p38 phosphorylation

Gp96 is an endoplasmic reticulum chaperone for multiple protein substrates. Its lack in intestinal macrophages of Crohn’s disease (CD) patients is correlated with loss of tolerance against the host gut flora. Gp96 has been stablished to be an essential chaperone for Toll-like receptors (TLRs). We studied the impact of gp96-knockdown on TLR-function in macrophages. TLR2 and TLR4 expression was only decreased but not abolished when gp96 was knocked-down in cell lines, whereas in a monocyte/macrophage specific knock-out mouse model (LysMCre) TLR4 was abolished, while TLR2 was still present. Lipopolysaccharide (LPS)-induced NF-κB activation was still observed in the absence of gp96, and gp96-deficient macrophages were able to up-regulate surface TLR4 upon LPS treatment, suggesting that there is another chaperone involved in the folding of TLR4 upon stress responses. Moreover, LPS-dependent pro-inflammatory cytokines were still expressed, although to a lesser extent in the absence of gp96, which reinforces the fact that gp96 is involved in regulating signaling cascades downstream of TLR4 are impaired upon loss of gp96. In addition, we have also found a reduced phosphorylation of ERK and p38 kinases and an impaired response upon CSF1R activation in gp96 deficient macrophages. Our findings indicate that the loss of gp96 not only impairs TLR4 signaling, but is also associated with a diminished phosphorylation of ERK and mitogen-activated stress kinases resulting in an impaired signalling through several receptors, including CSF1R.

Molecular classification of Crohn's disease reveals two clinically relevant subtypes

OBJECTIVE

The clinical presentation and course of Crohn's disease (CD) is highly variable. We sought to better understand the cellular and molecular mechanisms that guide this heterogeneity, and characterise the cellular processes associated with disease phenotypes.

DESIGN

We examined both gene expression and gene regulation (chromatin accessibility) in non-inflamed colon tissue from a cohort of adult patients with CD and control patients. To support the generality of our findings, we analysed previously published expression data from a large cohort of treatment-naïve paediatric CD and control ileum.

RESULTS

We found that adult patients with CD clearly segregated into two classes based on colon tissue gene expression-one that largely resembled the normal colon and one where certain genes showed expression patterns normally specific to the ileum. These classes were supported by changes in gene regulatory profiles observed at the level of chromatin accessibility, reflective of a fundamental shift in underlying molecular phenotypes. Furthermore, gene expression from the ilea of a treatment-naïve cohort of paediatric patients with CD could be similarly subdivided into colon-like and ileum-like classes. Finally, expression patterns within these CD subclasses highlight large-scale differences in the immune response and aspects of cellular metabolism, and were associated with multiple clinical phenotypes describing disease behaviour, including rectal disease and need for colectomy.

CONCLUSIONS

Our results strongly suggest that these molecular signatures define two clinically relevant forms of CD irrespective of tissue sampling location, patient age or treatment status.

Activation of TGF-β activated kinase 1 promotes colon mucosal pathogenesis in inflammatory bowel disease

The etiology and mechanisms for inflammatory bowel disease (IBD) are incompletely known. Determination of new, clinically important mechanisms for intestinal inflammation is imperative for developing effective therapies to treat IBD. We sought to define a widespread mechanism for colon mucosal inflammation via the activation of TGF‐β activated Kinase 1 (TAK1), a central regulator of cellular inflammatory actions. Activation of TAK1 and the downstream inflammatory signaling mediators was determined in pediatric patients with ulcerative colitis (UC) or Crohn's disease (CD) as well as in DSS‐induced and spontaneous IBD in mice. The role of TAK1 in facilitating intestinal inflammation in murine models of IBD was investigated by using (5Z)‐7‐Oxozeaenol, a highly selective pharmacological inhibitor of TAK1. We found hyper‐activation of TAK1 in patients with UC or CD and in murine models of IBD. Pharmacological inhibition of TAK1 prevented loss in body weight, disease activity, microscopic histopathology, infiltration of inflammatory cells in the colon mucosa, and elevated proinflammatory cytokine production in two murine models of IBD. We demonstrated that at the early phase of the disease activation of TAK1 is restricted in the epithelial cells. However, at a more advanced stage of the disease, TAK1 activation predominantly occurs in nonepithelial cells, especially in macrophages. These findings elucidate the activation of TAK1 as crucial in promoting intestinal inflammation. Thus, the TAK1 activation pathway may represent a suitable target to design new therapies for treating IBD in humans.

Intestinal macrophages in Peyer's patches, sacculus rotundus and appendix of Angora rabbit

The largest pool of macrophages in the body is harboured by the intestinal mucosa. As the principal phagocytic component of the immune system, macrophages are essential for maintaining mucosal homeostasis as they prevent commensal bacteria from adhering to mucosal epithelial cells. This study provides a RAM11 immunohistochemical and electron microscopic investigation of the existence, localization and distribution of intestinal macrophages in organized gut-associated lymphoid tissue (GALT), including Peyer's patches (PPs), the sacculus rotundus (SR) and the appendix, in the Angora rabbit. Although rabbit intestinal macrophages did not express the tissue macrophage marker macrosialin (CD68), they expressed RAM11. RAM11-positive intestinal macrophages were mostly localized to the subepithelial dome region, interfollicular area and germinal centres (GCs) of the GALT and the lamina propria or submucosa of the ileum and jejunum devoid of PPs and were also observed in the follicle-associated epithelium of PPs, but not in that of the SR and appendix. RAM11-positive macrophages containing engulfed apoptotic bodies were present in the GCs of the lymphoid follicles in the GALT. Electron microscopy further revealed multiple macrophages containing apoptotic bodies within the GCs of the follicles in the GALT. Some macrophage aggregations were observed in the GC and between the GC and the corona region of the follicles in the SR and appendix. Rabbit intestinal macrophages thus undertake both potent phagocytic activity and the efficient scavenging of apoptotic cells. Immunohistochemical data suggest that RAM11 can be reliably used for the determination of intestinal macrophages in the GALT of rabbits.

Persistent accumulation of gut macrophages with impaired phagocytic function correlates with SIV disease progression in macaques

The contribution of macrophages in the gastrointestinal tract to disease control or progression in HIV infection remains unclear. To address this question, we analyzed CD163⁺ macrophages in ileum and mesenteric lymph nodes (LN) from SIV-infected rhesus macaques with dichotomous expression of controlling MHC class I alleles predicted to be SIV controllers or progressors. Infection induced accumulation of macrophages into gut mucosa in the acute phase that persisted in progressors but was resolved in controllers. In contrast, macrophage recruitment to mesenteric LNs occurred only transiently in acute infection irrespective of disease outcome. Persistent gut macrophage accumulation was associated with CD163 expression on α4β7⁺ CD16⁺ blood monocytes and correlated with epithelial damage. Macrophages isolated from intestine of progressors had reduced phagocytic function relative to controllers and uninfected macaques, and the proportion of phagocytic macrophages negatively correlated with mucosal epithelial breach, lamina propria Escherichia coli density, and plasma virus burden. Macrophages in intestine produced low levels of cytokines regardless of disease course, while mesenteric LN macrophages from progressors became increasingly responsive as infection advanced. These data indicate that noninflammatory CD163⁺ macrophages accumulate in gut mucosa in progressive SIV infection in response to intestinal damage but fail to adequately phagocytose debris, potentially perpetuating their recruitment.

The Dual Role of Neutrophils in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD), including Crohn’s disease and ulcerative colitis, are characterised by aberrant immunological responses leading to chronic inflammation without tissue regeneration. These two diseases are considered distinct entities, and there is some evidence that neutrophil behaviour, above all other aspects of immunity, clearly separate them. Neutrophils are the first immune cells recruited to the site of inflammation, and their action is crucial to limit invasion by microorganisms. Furthermore, they play an essential role in proper resolution of inflammation. When these processes are not tightly regulated, they can trigger positive feedback amplification loops that promote neutrophil activation, leading to significant tissue damage and evolution toward chronic disease. Defective chemotaxis, as observed in Crohn’s disease, can also contribute to the disease through impaired microbe elimination. In addition, through NET production, neutrophils may be involved in thrombo-embolic events frequently observed in IBD patients. While the role of neutrophils has been studied in different animal models of IBD for many years, their contribution to the pathogenesis of IBD remains poorly understood, and no molecules targeting neutrophils are used and validated for the treatment of these pathologies. Therefore, it is crucial to improve our understanding of their mode of action in these particular conditions in order to provide new therapeutic avenues for IBD.

The Immunological Basis of Inflammatory Bowel Disease

Inflammatory bowel diseases (IBDs) are chronic ailments, Crohn's disease and ulcerative colitis being the most important. These diseases present an inflammatory profile and they differ according to pathophysiology, the affected area in the gastrointestinal tract, and the depth of the inflammation in the intestinal wall. The immune characteristics of IBD arise from abnormal responses of the innate and adaptive immune system. The number of Th17 cells increases in the peripheral blood of IBD patients, while Treg cells decrease, suggesting that the Th17/Treg proportion plays an important role in the development and maintenance of inflammation. The purpose of this review was to determine the current state of knowledge on the immunological basis of IBD. Many studies have shown the need for further explanation of the development and maintenance of the inflammatory process.

The effect of activated Mϕ1 on γδT cell-mediated killing of gastric cancer cells in vitro

A clear understanding of the interactions between classically activated macrophages (Mϕ1) and γδT cells may improve current therapeutic approaches, including that of immunotherapy for treating certain types of cancer. The present study aimed to expand the current knowledge by showing the effect of culture supernatants of Mϕ1 on the proliferation, cell surface marker expression and tumor suppression effects of γδT cells, and by exploring the potential mechanisms involved. In vitro, Mϕ1 were cultured by GM-CSF and IFN-γ. The isopentenyl pyrophosphate method was used to amplify human peripheral blood γδT cells. The surface markers of macrophages and γδT cells were detected by flow cytometry. The proliferation of γδT cells induced by the culture supernatants of Mϕ1 was investigated using the MTT assay. The lactate dehydrogenase method was used to detect the cytotoxicity of γδT cells on the SGC-7901 gastric cancer cell line. Ten days after cultivation, the percentage of γδT cells from the repertoire of naive cells, expanded from 4.21 to 91.27%. The percentage of cells expressing CD44 was 94%. The percentage of CD68 on cultured Mϕ1 was increased from 17.7 to 73.2%. The culture supernatants of Mϕ1 increased the proliferation of γδT cells compared with the control group (33.8% vs. 0, P<0.01). The culture supernatants of Mϕ1 increased the cytotoxicity of γδT cells compared with the control group (70.18 vs. 47.25%, P<0.01). In conclusion, the supernatant of cultured Mϕ1 promotes the proliferation of γδT cells and their cytotoxic effect on the SGC-7901 gastric cancer cell line.

Antigen sampling in the fish intestine

Antigen uptake in the gastrointestinal tract may induce tolerance, lead to an immune response and also to infection. In mammals, most pathogens gain access to the host though the gastrointestinal tract, and in fish as well, this route seems to be of significant importance. The epithelial surface faces a considerable challenge, functioning both as a barrier towards the external milieu but simultaneously being the site of absorption of nutrients and fluids. The mechanisms allowing antigen uptake over the epithelial barrier play a central role for maintaining the intestinal homeostasis and regulate appropriate immune responses. Such uptake has been widely studied in mammals, but also in fish, a number of experiments have been reported, seeking to reveal cells and mechanisms involved in antigen sampling. In this paper, we review these studies in addition to addressing our current knowledge of the intestinal barrier in fish and its anatomical construction.

The Microbiome of the Built Environment and Human Behavior: Implications for Emotional Health and Well-Being in Postmodern Western Societies

It is increasingly evident that inflammation is an important determinant of cognitive function and emotional behaviors that are dysregulated in stress-related psychiatric disorders, such as anxiety and affective disorders. Inflammatory responses to physical or psychological stressors are dependent on immunoregulation, which is indicated by a balanced expansion of effector T-cell populations and regulatory T cells. This balance is in part driven by microbial signals. The hygiene or "old friends" hypothesis posits that exposure to immunoregulation-inducing microorganisms is reduced in modern urban societies, leading to an epidemic of inflammatory disease and increased vulnerability to stress-related psychiatric disorders. With the global trend toward urbanization, humans are progressively spending more time in built environments, thereby, experiencing limited exposures to these immunoregulatory "old friends." Here, we evaluate the implications of the global trend toward urbanization, and how this transition may affect human microbial exposures and human behavior.

Regulatory T-cell depletion in the gut caused by integrin β7 deficiency exacerbates DSS colitis by evoking aberrant innate immunity

Integrin α4β7 controls lymphocyte trafficking into the gut and has essential roles in inflammatory bowel disease (IBD). The α4β7-blocking antibody vedolizumab is approved for IBD treatment; however, high dose of vedolizumab aggravates colitis in a small percentage of patients. Herein, we show that integrin β7 deficiency results in colonic regulatory T (Treg) cell depletion and exacerbates dextran sulfate sodium (DSS) colitis by evoking aberrant innate immunity. In DSS-treated β7-deficient mice, the loss of colonic Treg cells induces excessive macrophage infiltration in the colon via upregulation of colonic epithelial intercellular adhesion molecule 1 and increases proinflammatory cytokine expression, thereby exacerbating DSS-induced colitis. Moreover, reconstitution of the colonic Treg cell population in β7-deficient mice suppresses aberrant innate immune response in the colon and attenuates DSS colitis. Thus, integrin α4β7 is essential for suppression of DSS colitis as it regulates the colonic Treg cell population and innate immunity.

Translocation of microbes and changes of immunocytes in the gut of rapid- and slow-progressor Chinese rhesus macaques infected with SIVmac239

Human/simian immunodeficiency virus (HIV/SIV) infection can cause severe depletion of CD4(+) T cells in both plasma and mucosa; it also results in damage to the gut mucosa barrier, which makes the condition more conducive to microbial translocation. In this study, we used SIV-infected Chinese rhesus macaques to quantify the extent of microbial translocation and the function of immune cells in the entire gastrointestinal tract and to compare their differences between rapid and slow progressors. The results showed that in the slow progressors, microbial products translocated considerably and deeply into the lamina propria of the gut; the tissue macrophages had no significant differences compared with the rapid progressors, but there was a slightly higher percentage of mucosal CD8(+) T cells and a large amount of extracellular microbial products in the lamina propria of the intestinal mucosa of the slow progressors. The data suggested that although microbial translocation increased markedly, the mucosal macrophages and CD8(+) T cells were insufficient to clear the infiltrated microbes in the slow progressors. Also, therapies aimed at suppressing the translocation of microbial products in the mucosa could help to delay the progression of SIV disease.

Reversing Gut Damage in HIV Infection: Using Non-Human Primate Models to Instruct Clinical Research

Antiretroviral therapy (ART) has led to dramatic improvements in the lives of HIV-infected persons. However, residual immune activation, which persists despite ART, is associated with increased risk of non-AIDS morbidities. Accumulating evidence shows that disruption of the gut mucosal epithelium during SIV/HIV infections allows translocation of microbial products into the circulation, triggering immune activation. This disruption is due to immune, structural and microbial alterations. In this review, we highlighted the key findings of gut mucosa studies of SIV-infected macaques and HIV-infected humans that have revealed virus-induced changes of intestinal CD4, CD8 T cells, innate lymphoid cells, myeloid cells, and of the local cytokine/chemokine network in addition to epithelial injuries. We review the interplay between the host immune response and the intestinal microbiota, which also impacts disease progression. Collectively, these studies have instructed clinical research on early ART initiation, modifiers of microbiota composition, and recombinant cytokines for restoring gut barrier integrity.