Toll-Like Receptor 4 Contributes to Small Intestine Allograft Rejection

Immune cell profiling in intestinal transplantation

Since the first published case study of human intestinal transplantation in 1967, there have been significant studies of intestinal transplant immunology in both animal models and humans. An improved understanding of the profiles of different immune cell subsets is critical for understanding their contributions to graft outcomes. While different studies have focused on the contribution of one or a few subsets to intestinal transplant, no study has integrated these data for a comprehensive overview of immune dynamics after intestinal transplant. Here, we provide a systematic review of the literature on different immune subsets and discuss their roles in intestinal transplant outcomes on multiple levels, focusing on chimerism and graft immune reconstitution, clonal alloreactivity, and cell phenotype. In Sections 1, 2 and 3, we lay out a shared framework for understanding intestinal transplant, focusing on the mechanisms of rejection or tolerance in the context of mucosal immunology and illustrate the unique role of the bidirectional graft-versus-host (GvH) and host-versus-graft (HvG) alloresponse. In Sections 4, 5 and 6, we further expand upon these concepts as we discuss the contribution of different cell subsets to intestinal transplant. An improved understanding of intestinal transplantation immunology will bring us closer to maximizing the potential of this important treatment.

Study the mRNA level of IL-27/IL-27R pathway molecules in kidney transplant rejection

BACKGROUND

Renal transplantation stands as the sole remedy for individuals afflicted with end-stage renal diseases, and safeguarding them from transplant rejection represents a vital, life-preserving endeavor posttransplantation. In this context, the impact of cytokines, notably IL-27, assumes a critical role in managing immune responses aimed at countering rejection. Consequently, this investigation endeavors to explore the precise function of IL-27 and its associated cytokines in the context of kidney transplant rejection.

METHODS

The study involved the acquisition of blood samples from a cohort of participants, consisting of 61 individuals who had undergone kidney transplantation (comprising 32 nonrejected patients and 29 rejected patients), and 33 healthy controls. The expression levels of specific genes were examined using SYBR Green Real-time PCR. Additionally, the evaluation encompassed the estimation of the ROC curve, the assessment of the relationship between certain blood factors, and the construction of protein-protein interaction networks for the genes under investigation.

RESULTS

Significant statistical differences in gene expression levels were observed between the rejected group and healthy controls, encompassing all the genes examined, except for TLR3 and TLR4 genes. Moreover, the analysis of the Area Under the Curve (AUC) revealed that IL-27, IL-27R, TNF-α, and TLR4 exhibited greater significance in discriminating between the two patient groups. These findings highlight the potential importance of IL-27, IL-27R, TNF-α, and TLR4 as key factors for distinguishing between individuals in the rejected group and those in the healthy control group.

CONCLUSIONS

In the context of kidney rejections occurring within the specific timeframe of 2 weeks to 2 months post-transplantation, it is crucial to emphasize the significance of cytokines mRNA level, including IL-27, IL-27R, TNF-α, and TLR4, in elucidating and discerning the diverse immune system responses. The comprehensive examination of these cytokines' mRNA level assumes considerable importance in understanding the intricate mechanisms underlying kidney rejection processes during this critical period.

Innovations in Immunosuppression for Intestinal Transplantation

It has been 57 years since the first intestinal transplant. An increased incidence of graft rejection has been described compared to other solid organ transplants due to high immunogenicity of the bowel, which in health allows the balance between of dietary antigen with defense against pathogens. Expanding clinical experience, knowledge of gastrointestinal physiology and immunology have progress post-transplant immunosuppressive drug regimens. Current regimes aim to find the window between prevention of rejection and the risk of infection (the leading cause of death) and malignancy. The ultimate aim is to achieve graft tolerance. In this review we discuss advances in mucosal immunology and technologies informing the development of new anti-rejection strategies with the hope of improved survival in the next generation of transplant recipients.

TLR2 and TLR4 mRNA expression levels in liver transplant patients with acute rejection

Toll-like receptors (TLRs) have important role in transplant outcomes by activating the innate immune system and production of pro-inflammatory cytokines, leading to graft rejection. We assessed the expression level of TL2 and TLR4 in acute rejection (AR) on the 1st and 7th^-day post-transplantation. TLR2 and TLR4 expressions were evaluated by real-time PCR in both the AR group (n = 50) and non-AR (n = 50), compared with the control group. Also, the correlation of the expression levels of TLRs between both the 1st and 7th day was analyzed. ROC curve analysis was used to determine the cut-off value for TLRs expression. TLR4 mRNA expression was significantly up-regulated in AR patients vs. the controls on the 1st day (p ≤ 0.05) and it was down-regulated in non-AR vs. controls on the 1st day (p ≤ 0.05). Also, TLR4 expression had decreased in both AR and non-AR groups vs. control on the 7th day (p ≤ 0.05). Both TLR2 and TLR4 expression in comparison to non-AR had increased in the AR group on the 7th day (p ≤ 0.05). TLR2 expression positively correlated between 1st and 7th day in AR (r = 0.3, (p ≤ 0.05) and non-AR group (r = 0.2, p ≤ 0.05). ROC curve analysis showed a cut-off value of TLR2 up to 0.98 with sensitivity 71.05 (95%CI = 54.1-84.6) and specificity 63.27 (95%CI = 48.3-76.6) that could distinguish between AR and non-AR group (p ≤ 0.05). The data support that both TLR2 and TLR4 expression have an effective role in AR after liver transplantation and could be used as possible biomarkers for AR to choose better therapeutic strategies based on immunological aspects.

Deferoxamine preconditioning activated hypoxia-inducible factor-1α and MyD88-dependent Toll-like receptor 4 signaling in intestinal stem cells

BACKGROUND/PURPOSE

Toll-like receptors (TLRs) are important regulators of innate immunity, and TLR4 pathway can regulate the survival, migration, and differentiation of stem cells, including intestinal stem cells (ISCs). Deferoxamine (DFO), a hypoxia-mimic compound, can activate the proliferation of ISCs. In this study, we investigated the response of TLR4 signaling to DFO-induced hypoxia in cultured ISCs in vitro.

METHODS

After DFO treatment, the crypt organoid number was counted, and the expression levels of Lgr5, Hsp70, HMGB1, HIF-1α, TLR4, MyD88, TRIF, and TRAM in ISCs were examined using QPCR and Western blotting. The chemical inhibitors of different signaling molecules were then used to determine their role in DFO-induced change in ISCs.

RESULTS

The expression levels of Lgr5, HIF-1α, TLR4, MyD88, and TRIF in ISCs increased after DFO treatment, with peak expression of these molecules 6h after DFO treatment. In addition, DFO-induced gene expression of Lgr5 and HIF-1α was partially reversed by pretreatment with the inhibitor of TLR4 or MyD88, but not TRIF inhibitor. Inhibition of HIF-1α also resulted in partial downregulation of DFO-induced elevation of Lgr5 and TLR4.

CONCLUSIONS

These results demonstrated that DFO treatment activated HIF-1α and the TLR4-MyD88 signaling pathway, which might mediate the activation of ISCs.

Gut microbiota and its implications in small bowel transplantation

The gut microbiota is mainly composed of a diverse population of commensal bacterial species and plays a pivotal role in the maintenance of intestinal homeostasis, immune modulation and metabolism. The influence of the gut microbiota on solid organ transplantation has recently been recognized. In fact, several studies indicated that acute and chronic allograft rejection in small bowel transplantation (SBT) is closely associated with the alterations in microbial patterns in the gut. In this review, we focused on the recent findings regarding alterations in the microbiota following SBTand the potential roles of these alterations in the development of acute and chronic allograft rejection. We also reviewed important advances with respect to the interplays between the microbiota and host immune systems in SBT. Furthermore, we explored the potential of the gut microbiota as a microbial marker and/or therapeutic target for the predication and intervention of allograft rejection and chronic dysfunction. Given that current research on the gut microbiota has become increasingly sophisticated and comprehensive, large cohort studies employing metagenomic analysis and multivariate linkage should be designed for the characterization of host-microbe interaction and causality between microbiota alterations and clinical outcomes in SBT. The findings are expected to provide valuable insights into the role of gut microbiota in the development of allograft rejection and other transplant-related complications and introduce novel therapeutic targets and treatment approaches in clinical practice.

Adaptive and innate immune responses in a rat orthotopic lung transplant model of chronic lung allograft dysfunction

Acute rejection and respiratory infections are major risk factors for chronic lung allograft dysfunction (CLAD) after lung transplantation. To shed light on the enigmatic etiology of CLAD, we test the following hypotheses using a new experimental model: (i) Alloimmune-independent pulmonary inflammation reactivates alloimmunity. (ii) Alloimmunity enhances the susceptibility of the graft toward pathogen-associated molecular patterns. Pulmonary Fischer 344 to Lewis rat allografts were treated with lipopolysaccharide (LPS), which consistently results in lesions typical for CLAD. Grafts, local lymph nodes, and spleens were harvested before (day 28) and after LPS application (days 29, 33, and 40) for real-time RT-PCR and immunohistochemistry. Mixed lymphocyte reactions were performed on day 33. Four weeks after transplantation, lung allografts displayed mononuclear infiltrates compatible with acute rejection and overexpressed most components of the toll-like receptor system. Allografts but not secondary lymphoid organs expressed increased levels of Th1-type transcription factors and cytokines. LPS induced macrophage infiltration as well as mRNA expression of pro-inflammatory cytokines and effector molecules of innate immunity. Unexpectedly, T-cell reactivity was not enhanced by LPS. We conclude that prevention of CLAD might be accomplished by local suppression of Th1 cells in stable grafts and by controlling innate immunity during alloimmune-independent pulmonary inflammation.

Modulation of immune responses following solid organ transplantation by microRNA

Organ transplantation, an accepted treatment for end stage organ failure, is often complicated by allograft rejection and disease recurrence. In this review we will discuss the potential role of microRNAs in allograft immunity especially leading to rejection of the transplanted organ. microRNAs (miRNAs), originally identified in C. elegans, are short non-coding 21-24 nucleotide sequences that bind to its complementary sequences in functional messenger RNAs and inhibits post-translational processes through RNA duplex formation resulting in gene silencing (Lau et al., 2001). Gene specific translational silencing by miRNAs regulates pathways for immune responses such as development of innate immunity, inflammation, T-cell and B-cell differentiation and signaling that are implicated in various stages of allograft rejection. miRNAs also play a role in development of post-transplant complicacies like fibrosis, cirrhosis, carcinogenesis often leading to graft loss and poor patient outcome. Recent advancements in the methods for detecting and quantifying miRNA in tissue biopsies, as well as in serum and urine samples, has led to identification of specific miRNA signatures in patients with allograft rejection and have been utilized to predict allograft status and survival. Therefore, miRNAs play a significant role in post-transplant events including allograft rejection, disease recurrence and tumor development impacting patient outcome.

Induction of alloimmune tolerance in heart transplantation through gene silencing of TLR adaptors

Toll-like receptors (TLRs) activate biochemical pathways that evoke activation of innate immunity, which leads to dendritic cell (DC) maturation and initiation of adaptive immune responses that provoke allograft rejection. We aimed to prolong allograft survival by selectively inhibiting expression of the common adaptors of TLR signaling, namely MyD88 and TRIF, using siRNA. In vitro we demonstrated that blocking expression of MyD88 and TRIF led to reduced DC maturation. In vivo treatment of recipients with MyD88 and TRIF siRNA significantly prolonged allograft survival in the BALB/c > C57BL6 cardiac transplant model. Moreover, the combination of MyD88 and TRIF siRNA along with a low dose of rapamycin further extended the allograft survival (88.8 ± 7.1 days). Tissue histopathology demonstrated an overall reduction in lymphocyte interstitium infiltration, vascular obstruction and hemorrhage in mice treated with MyD88 and TRIF siRNA vector plus rapamycin. Furthermore, treatment was associated with an increase in the numbers of CD4(+) CD25(+) FoxP3(+) regulatory T cells and Th2 deviation. To our knowledge, this study is the first demonstration of prolonging the survival of allogeneic heart grafts through gene silencing of TLR signaling adaptors, highlighting the therapeutic potential of siRNA in clinical transplantation.

Innate immunity and organ transplantation: focus on lung transplantation

Ischemia reperfusion injury (IRI) that occurs with solid organ transplantation activates the innate immune system to induce inflammation. This leads to enhanced acute allograft rejection, impaired transplant tolerance and accelerated progression of chronic rejection. In this review, we discuss the innate immune signaling pathways that have been shown to play a role in organ transplantation. In particular, we focus on Toll-like receptor signaling pathways and how they have influenced outcomes after organ transplantation both experimentally and from clinical studies. Furthermore, we describe the substances that trigger the innate immune system after transplantation and several of the key cellular mediators of inflammation. We specifically point out unique aspects of activation of the innate immune system after lung transplantation. Finally, we discuss the areas that should be investigated in the future to more clearly understand the influence of the innate immune system after organ transplantation.

The pig as a preclinical model for intestinal ischemia-reperfusion and transplantation studies

Small bowel transplantation has become an established procedure for treatment of irreversible intestinal failure. In this procedure, primary ischemia and reperfusion is inevitable and will lead to some level of tissue injury. Both clinical and experimental data demonstrate that events occurring at the time of transplantation, called ischemia reperfusion injury (IRI), may have deleterious short- and long-term effects, manifesting as increased episodes of acute rejection and chronic allograft dysfunction. Recently, the acute phase of IRI has been increasingly viewed as part of the innate immune response to the lack of vascular perfusion and oxygen. Research on intestinal IRI that aims to understand its mechanisms and the means to reduce its impact on morbidity and mortality related to intestinal transplantations is considered important because a link has been suggested between innate immunity, adaptive immune responses and organ regeneration, and thus long-term graft function. This article provides an overview of porcine models commonly used to study intestinal reperfusion injury and to evaluate intestinal transplant protocols. It also updates the current knowledge obtained from this model, establishing the pig as a reference standard in intestinal transplantation research.

Characterization of the ileal microbiota in rejecting and nonrejecting recipients of small bowel transplants

Small bowel transplantation can be a life-preserving procedure for patients with irreversible intestinal failure. Allograft rejection remains a major source of morbidity and mortality and its accurate diagnosis and treatment are critical. In this study, we used pyrosequencing of 16S ribosomal RNA gene tags to compare the composition of the ileal microbiota present during nonrejection, prerejection and active rejection states in small bowel transplant patients. During episodes of rejection, the proportions of phylum Firmicutes (p < 0.001) and the order Lactobacillales (p < 0.01) were significantly decreased, while those of the phylum Proteobacteria, especially the family Enterobacteriaceae, were significantly increased (p < 0.005). Receiver-operating characteristic analysis revealed that relative proportions of several bacterial taxa in ileal effluents and especially Firmicutes, could be used to discriminate between nonrejection and active rejection. In conclusion, the findings obtained during this study suggest that small bowel transplant rejection is associated with changes in the microbial populations in ileal effluents and support microbiota profiling as a potential diagnostic biomarker of rejection. Future studies should investigate if the dysbiosis that we observed is a cause or a consequence of the rejection process.

Innate immunity in the small intestine

PURPOSE OF REVIEW

This article reviews the most recent publications on innate immunity in the small intestine. We will go over the innate immune receptors that act as sensors of microbial presence or cell injury, Paneth cells as the main epithelial cell type that secrete antimicrobial peptides, and mucosal production of immunoglobulin A (IgA). In addition, we will give an update on examples of imbalance of the innate immune response resulting in clinical disease with the most relevant example being Crohn's disease.

RECENT FINDINGS

Toll-like receptors (TLRs) are involved in B-cell homing to the intestine, rejection of small intestinal allografts, and recruitment of mast cells. The TLR adaptor Toll/interleukin-1 receptor domain-containing adapter-inducing interferon-β is necessary to activate innate immunity after Yersinia enterocolitica infection. Moreover, MyD88 is required to keep the intestinal microbiota under control and physically separated from the epithelium, and RegIIIγ is responsible for the bacterial segregation from the lining epithelial cells. In Crohn's disease, ATG16L1 T300A variant promotes a proinflammatory response; and miR-196 downregulates a protective immunity-related GTPase family M protein (IRGM) polymorphism leading to impaired clearance of adherent Escherichia coli in the intestine.

SUMMARY

The intestine is continuously exposed to dietary and microbial antigens. The host has to maintain intestinal homeostasis to keep the commensal and pathogenic bacteria under control. Some of the mechanisms to do so are by expression of innate immune receptors, production of antimicrobial peptides, secretion of IgA, or autophagy of intracellular bacteria. Unfortunately, in some cases the innate immune response fails to protect the host and chronic inflammation, transplant rejection, or other disorders may occur.

Effect of polyethylene glycol in pig intestinal allotransplantation without immunosuppression

OBJECTIVES

We evaluated whether IGL-1, a graft preservation solution containing polyethylene glycol, improves the outcome of small bowel grafts in comparison to the University of Wisconsin (UW) solution in a pig allotransplantation model.

MATERIALS AND METHODS

Seventeen pigs were randomly allocated to group 1 (n = 10; intestinal allotransplantation with IGL-1) and group 2 (n = 7; allotransplantation with UW). Pigs received no immunosuppression and were sacrificed on postoperative d (POD) 8. Intestinal specimens were obtained from the animal immediately before cold flushing (T0), 2 h after graft reperfusion (T1), and at sacrifice (T2).

RESULTS

Survival rate to POD 8 was 50% in group 1 compared with 16% in group 2 (P < 0.05); 62% of pigs in group 1 did not present any acute cellular rejection (ACR) compared to 16% in group 2 (P < 0.05). Severe ACR rate was 25% in group 1 and 66% in group 2 (P < 0.05). iNOS activity and intestinal caspase 3 levels increased significantly between T0 and T1 in group 1 compared to group 2 (P < 0.05). Cell necrosis increased significantly between TO and T1 in group 2 compared with group 1 (P < 0.05) whereas cell apoptosis was significantly higher at T1 compared with T0 in group 1 in comparison to group 2.

CONCLUSIONS

Our results show that IGL-1 improves intestinal graft viability as compared to UW solution, possibly by reducing graft immunogenicity and by favoring intestinal epithelial repair.