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

Secreted glucose regulated protein78 ameliorates DSS-induced mouse colitis

The secreted form of 78-kDa glucose-regulated protein (sGRP78) has been widely reported for its property in aiding resolution of inflammatory. However, little is known on its potential in the treatment of colitis. To investigate the expression pattern and functional outcome of GRP78 in ulcerative colitis, its expression was measured in human and murine colitis samples. It was found that GRP78 was spontaneously secreted to a high level in gut, which is a physiological site of immune tolerance. During the active phase of DSS-induced colitis, the sGRP78 level was significantly reduced but rebounded quickly during resolving phase, making it a potential candidate for the treatment of colitis. In the following experiments, the administration of sGRP78 was proved to decrease susceptibility to experimental colitis, as indicated by an overall improvement of intestinal symptoms, restoration of TJ integrity, decreased infiltration of immune cells and impaired production of inflammatory cytokines. And specific cleavage of endogenous sGRP78 could aggravate DSS colitis. Adoptive transfer of sGRP78-conditioned BMDMs reduced inflammation in the gut. We linked sGRP78 treatment with altered macrophage biology and skewed macrophage polarization by inhibiting the TLR4-dependent MAP-kinases and NF-κB pathways. Based on these studies, as a naturally occurring immunomodulatory molecule, sGRP78 might be an attractive novel therapeutic agent for acute intestinal inflammation.

Inflammation induces pro-NETotic neutrophils via TNFR2 signaling

Cytokines released during chronic inflammatory diseases induce pro-inflammatory properties in polymorphonuclear neutrophils (PMNs). Here, we describe the development of a subgroup of human PMNs expressing CCR5, termed CCR5⁺ PMNs. Auto- and paracrine tumor necrosis factor (TNF) signaling increases intracellular neutrophil elastase (ELANE) abundance and induces neutrophil extracellular traps formation (NETosis) in CCR5⁺ PMNs, and triggering of CCR5 amplifies NETosis. Membranous TNF (mTNF) outside-in signaling induces the formation of reactive oxygen species, known activators of NETosis. In vivo, we find an increased number of CCR5⁺ PMNs in the peripheral blood and inflamed lamina propria of patients with ulcerative colitis (UC). Notably, failure of anti-TNF therapy is associated with higher frequencies of CCR5⁺ PMNs. In conclusion, we identify a phenotype of pro-NETotic, CCR5⁺ PMNs present in inflamed tissue in vivo and inducible in vitro. These cells may reflect an important component of tissue damage during chronic inflammation and could be of diagnostic value.

Reproducing the human mucosal environment ex vivo: inflammatory bowel disease as a paradigm

PURPOSE OF REVIEW

The medical management of inflammatory bowel disease (IBD) remains problematic with a pressing need for innovation in drug development as well as delivery of personalized therapies. Both the disease's inherent pathophysiologic complexity and heterogeneity in its etiology conspire in making it difficult to accurately model for either the purposes of basic research or drug development. Multiple attempts at creating meaningful experimental models have fallen short of adequately recapitulating the disease and most do not capture any aspect of the cause or the effects of patient heterogeneity that underlays most of the difficulties faced by physicians and their patients. In vivo animal models, tissue culture systems, and more recent synthetic biology approaches are all too simplistically reductionist for the task. However, ex vivo culture platforms utilizing patient biopsies offer a system that more closely mimics end-stage disease processes that can be studied in detail and subjected to experimental manipulations.

RECENT FINDINGS

Recent studies describe further optimization of mucosal explant cultures in order to increase tissue viability and maintain a polarized epithelial layer. Current applications of the platform include studies of the interplay between the epithelial, immune and stromal compartment of the intestinal tissue, investigation of host-microbial interactions, preclinical evaluation of candidate drugs and uncovering mechanisms of action of established or emerging treatments for IBD.

SUMMARY

Patient explant-based assays offer an advanced biological system in IBD that recapitulates disease complexity and reflects the heterogeneity of the patient population. In its current stage of development, the system can be utilized for drug testing prior to the costlier and time-consuming evaluation by clinical trials. Further refinement of the technology and establishment of assay readouts that correlate with therapeutic outcomes will yield a powerful tool for personalized medicine approaches in which individual patient responses to available treatments are assessed a priori, thus reducing the need for trial and error within the clinical setting.

Human monocytes downregulate innate response receptors following exposure to the microbial metabolite n-butyrate

Introduction

Hyporesponsiveness of human lamina propria immune cells to microbial and nutritional antigens represents one important feature of intestinal homeostasis. It is at least partially mediated by low expression of the innate response receptors CD11b, CD14, CD16 as well as the cystine‐glutamate transporter xCT on these cells. Milieu‐specific mechanisms leading to the down‐regulation of these receptors on circulating monocytes, the precursor cells of resident macrophages, are mostly unknown.

Methods

Here, we addressed the question whether the short chain fatty acid n‐butyrate, a fermentation product of the mammalian gut microbiota exhibiting histone deacetylase inhibitory activity, is able to modulate expression of these receptors in human circulating monocytes.

Results

Exposure to n‐butyrate resulted in the downregulation of CD11b, CD14, as well as CD16 surface expression on circulating monocytes. XCT transcript levels in circulating monocytes were also reduced following exposure to n‐butyrate. Importantly, treatment resulted in the downregulation of protein and gene expression of the transcription factor PU.1, which was shown to be at least partially required for the expression of CD16 in circulating monocytes. PU.1 expression in resident macrophages in situ was observed to be substantially lower in healthy when compared to inflamed colonic mucosa.

Conclusions

In summary, the intestinal microbiota may support symbiosis with the human host organism by n‐butyrate mediated downregulation of protein and gene expression of innate response receptors as well as xCT on circulating monocytes following recruitment to the lamina propria. Downregulation of CD16 gene expression may at least partially be caused at the transcriptional level by the n‐butyrate mediated decrease in expression of the transcription factor PU.1 in circulating monocytes.

Standardization of a human organ culture model of intestinal inflammation and its application for drug testing

Targeting early molecular events in intestinal inflammation may represent a useful therapeutic strategy for maintaining remission in inflammatory bowel disease. Recently, we established an intestinal organ culture model (LEL model), which allows to study the initiation of an intestinal inflammatory response in human tissue. In this model, EDTA-mediated depletion of epithelial cells of colonic mucosa results in an instantaneous inflammatory response in resident lamina propria cells, which shows features of intestinal inflammation in vivo. Furthermore, activated immune cells emigrate from the lamina propria onto the luminal side of the basement membrane. Here, we standardize the LEL model and explore its suitability for drug testing. To this end, human mucosal punches of defined surface area were prepared, depleted of epithelial cells, and cultured at an optimized ratio of medium volume/punch area. The intra-assay variability of measurements of inflammatory parameters ranged from 13% for cell migration to 19% for secretion and 30% for tissue gene expression, respectively, of the inflammatory mediators IL-8 and IL-6. Importantly, known suppressive effects of dexamethasone, a drug employed for the treatment of inflammatory bowel diseases, on leucocyte migration, IL8, IL6, and TNF-α production as well as CD86 surface expression by myeloid cells were observed in this model. In conclusion, the present results suggest that the LEL model may represent a useful human experimental system not only for studying initial activation mechanisms in intestinal inflammation but also for evaluating drug compounds for the treatment of mucosal inflammation.

Immunomodulation of human intestinal T cells by the synthetic CD80 antagonist RhuDex®

Deregulated activation of mucosal lamina propria T cells plays a central role in the pathogenesis of intestinal inflammation. One of the means to attenuate T cell activation is by blocking the CD28/CD80 co-stimulatory pathway. Here we investigate RhuDex®, a small molecule that binds to human CD80, for its effects on the activation of lamina propria T cells employing a gut-culture model of inflammation. To this end, lamina propria leukocytes (LPL) and peripheral blood lymphocytes (PBL) were stimulated either through the CD3/T-cell-receptor complex or the CD2-receptor (CD2) employing agonistic monoclonal antibodies. Co-stimulatory signals were provided by CD80/CD86 present on lamina propria myeloid cells or LPS-activated peripheral blood monocytes. Results show that RhuDex® caused a profound reduction of LPL and PBL proliferation, while Abatacept (CTLA-4-Ig) inhibited LPL proliferation to a small degree, and had no effect on PBL proliferation. Furthermore, Abatacept significantly inhibited IL-2, TNF-α, and IFN-γ release from LPL, primarily produced by CD4⁺ T cells, where IL-2 blockage was surprisingly strong, suggesting a down-regulating effect on regulatory T cells. In contrast, in the presence of RhuDex®, secretion of IL-17, again mostly by CD4⁺ T cells, and IFN-γ was inhibited in LPL and PBL, yet IL-2 remained unaffected. Thus, RhuDex® efficiently inhibited lamina propria and peripheral blood T-cell activation in this pre-clinical study making it a promising drug candidate for the treatment of intestinal inflammation.