CD4-Positive T Cells and M2 Macrophages Dominate the Peritoneal Infiltrate of Patients with Encapsulating Peritoneal Sclerosis

Sterile inflammation of peritoneal membrane caused by peritoneal dialysis: focus on the communication between immune cells and peritoneal stroma

Peritoneal dialysis is a widely used method for treating kidney failure. However, over time, the peritoneal structure and function can deteriorate, leading to the failure of this therapy. This deterioration is primarily caused by infectious and sterile inflammation. Sterile inflammation, which is inflammation without infection, is particularly concerning as it can be subtle and often goes unnoticed. The onset of sterile inflammation involves various pathological processes. Peritoneal cells detect signals that promote inflammation and release substances that attract immune cells from the bloodstream. These immune cells contribute to the initiation and escalation of the inflammatory response. The existing literature extensively covers the involvement of different cell types in the sterile inflammation, including mesothelial cells, fibroblasts, endothelial cells, and adipocytes, as well as immune cells such as macrophages, lymphocytes, and mast cells. These cells work together to promote the occurrence and progression of sterile inflammation, although the exact mechanisms are not fully understood. This review aims to provide a comprehensive overview of the signals from both stromal cells and components of immune system, as well as the reciprocal interactions between cellular components, during the initiation of sterile inflammation. By understanding the cellular and molecular mechanisms underlying sterile inflammation, we may potentially develop therapeutic interventions to counteract peritoneal membrane damage and restore normal function.

Encapsulating Peritoneal Sclerosis in a Patient Receiving Peritoneal Dialysis and Glucocorticoid Therapy

Encapsulating peritoneal sclerosis (EPS) is a fatal complication of peritoneal dialysis. A 68-year-old man undergoing peritoneal dialysis for 10 years started receiving daily 50 mg of glucocorticoids for idiopathic pulmonary sclerosis. At the transition to hemodialysis, a peritoneal biopsy was performed, which demonstrated mild histological changes, including no fibrin formation and mild T lymphocyte infiltration at the time of 6.5 mg glucocorticoids. However, five months later, he developed EPS when receiving 2.5 mg glucocorticoids. Afterward, over 5 mg daily glucocorticoids were required to avoid the recurrence of EPS. These findings suggest that glucocorticoids may conceal peritoneal inflammation, a main contributor to EPS.

Pathophysiology of encapsulating peritoneal sclerosis: lessons from findings of the past three decades in Japan

Encapsulating peritoneal sclerosis (EPS), a condition with a high mortality rate, is a serious complication of peritoneal dialysis (PD). In Japan, EPS became a central issue in the clinical setting during the mid-90s and the beginning of this century. However, following the introduction of biocompatible neutral PD solutions containing lower levels of glucose degradation products, the incidence and clinical severity of EPS has been greatly lessened. During the past three decades, the etiology of EPS has been elucidated by findings obtained by peritoneal biopsy, laparoscopy, and surgical intervention. Accumulating findings suggest the need for a paradigm change on the nature of EPS pathophysiology; notably, EPS appears not to reflect peritoneal sclerosis per se, but rather the formation of a neo-membrane as a biological reaction to peritoneal injury. This narrative review looks back on the history of EPS in Japan, and discusses EPS pathophysiology, the impact of neutral PD solution on peritoneal protection, and a future novel diagnostic approach, ultra-fine endoscope, for the identification of patients at high risk of EPS.

A Novel Technique for the Generation of Substantial Numbers of Functional Resident T Cells from Kidney Tissue

Studying functionality and antigen-specificity of resident kidney T cells derived from a kidney biopsy is hampered by the lack of sufficient numbers of T cells obtained by the standard method of enzymatic tissue dissociation. Enzymatic dissociation of kidney tissue was compared to a novel method of whole kidney tissue culture allowing T cells to migrate into the medium in the presence of exogenous IL-2 and IL-15. T cell numbers were quantified and phenotype of resident T cells (CD69+CD103+/−), TCR Vβ repertoire and functional characteristics were analyzed with multi-parameter flow cytometry. Renal tissue culture for four weeks in the presence of exogenous IL-2 and IL-15 yielded significantly higher numbers of T cells (1.3 × 104/mm3) when compared to cultures without exogenous cytokines (71/mm3) or direct isolation by enzymatic dissociation (662/mm3 T cells, p < 0.05). The proportion of T cells with a resident phenotype did not change in the tissue culture; percentages amounted to 87.2% and 85.1%, respectively. In addition, frequencies of CD4+, CD8+, CD4−CD8−, T cells and MAIT T cells remained similar. For both CD4+ and CD8+, T cells had a more differentiated memory phenotype after tissue culture, but the distribution of TCR Vβ families did not change. In addition, the predominant Th1 cytokine secretion profile and poly-functionality of resident kidney T cell remained intact. T cell proliferation potential was not affected, excluding exhaustion and enrichment of BKV- and CMV-reactive resident T cells was observed. In conclusion, the kidney tissue culture method yields significantly increased numbers of resident T cells without major effects on composition and functionality.

IL-17A as a Potential Therapeutic Target for Patients on Peritoneal Dialysis

Chronic kidney disease (CKD) is a health problem reaching epidemic proportions. There is no cure for CKD, and patients may progress to end-stage renal disease (ESRD). Peritoneal dialysis (PD) is a current replacement therapy option for ESRD patients until renal transplantation can be achieved. One important problem in long-term PD patients is peritoneal membrane failure. The mechanisms involved in peritoneal damage include activation of the inflammatory and immune responses, associated with submesothelial immune infiltrates, angiogenesis, loss of the mesothelial layer due to cell death and mesothelial to mesenchymal transition, and collagen accumulation in the submesothelial compact zone. These processes lead to fibrosis and loss of peritoneal membrane function. Peritoneal inflammation and membrane failure are strongly associated with additional problems in PD patients, mainly with a very high risk of cardiovascular disease. Among the inflammatory mediators involved in peritoneal damage, cytokine IL-17A has recently been proposed as a potential therapeutic target for chronic inflammatory diseases, including CKD. Although IL-17A is the hallmark cytokine of Th17 immune cells, many other cells can also produce or secrete IL-17A. In the peritoneum of PD patients, IL-17A-secreting cells comprise Th17 cells, γδ T cells, mast cells, and neutrophils. Experimental studies demonstrated that IL-17A blockade ameliorated peritoneal damage caused by exposure to PD fluids. This article provides a comprehensive review of recent advances on the role of IL-17A in peritoneal membrane injury during PD and other PD-associated complications.

The effect of rituximab on encapsulated peritoneal sclerosis in an experimental rat model

Background/aim

 Peritoneal sclerosis may be observed in varied manifestations. However, the most serious form is the encapsulated peritoneal sclerosis. We researched the effect of rituximab on peritoneal fibrosis in an experimental rat model.

Materials and methods

Twenty-four Wistar Albino rats were divided into 4 equal groups. During weeks 0–3; group I received isotonic saline (IS) solution, group II, group III, and group IV received chlorhexidine gluconate (CG) via intraperitoneal (i.p.) route. In the next 3 weeks nothing adminestred to both group I and group II but IS solution was adminestred to group III via i.p. route and 375 mg/m2/week rituximab was applied intravenously on days 21, 28, and 35 to group IV. Fibrosis, peritoneal thickness, and inflammation were evaluated. Immunohistochemical methods used for the detection of matrix MMP-2, TGF-β1, and VGEF expressions.

Results

  The rituximab (group IV) had significantly lower fibrosis and peritoneal thickness scores than the group II and III (P < 0.001). TGF-β1 and VEGF expressions were significantly lower in the rituximab group than in the group II and III (P < 0.001).Conclusion: We found that rituximab had a significant effect on the peritoneal thickness, total fibrosis, TGF-β1 and VGEF scores which were induced by CG.

High glucose contributes to the polarization of peritoneal macrophages to the M2 phenotype in vivo and in vitro

Glucose is the primary osmotic medium used in most peritoneal dialysis (PD) solutions, and long‑term exposure to high glucose is a major contributor to peritoneal fibrosis. Our previous study revealed that M2 macrophages participate in the development of PD‑related fibrosis in a rat model. In the present study, the effects of high glucose on peritoneal macrophage polarization in vivo and in vitro were further evaluated. Continuous ambulatory PD (CAPD) patients with an overnight dwell of 1.5 or 2.5% glucose dialysate were recruited for this study. Overnight effluent samples from patients with CAPD (2,000 ml) were centrifuged to collect cells from the peritoneal cavity. J774A.1 cells (murine macrophages from ascites) were cultured in different concentrations of glucose. Macrophage phenotype markers were detected by flow cytometry. The levels of cytokines in PD effluent and the supernatant of murine macrophages were detected by enzyme‑linked immunosorbent assays. The activity of arginase was determined by quantitative colorimetric analysis. In total, 107 CAPD subjects (92 patients using 1.5% glucose dialysate and 15 patients using 2.5% glucose dialysate) were recruited. The percentage of M1 macrophages (CD14‑ and CCr7‑positive cells) in the 1.5 and 2.5% glucose dialysate groups was 23.0±13.3 and 24.9±12.0%, respectively. The difference was not significant (P>0.05). The percentage of M2 macrophages (CD14‑ and CD206‑positive cells) in the 1.5% glucose dialysate group (36.2±11.4%) was significantly decreased compared to the 2.5% glucose dialysate group (43.2±7.4%) (P<0.05). Murine macrophages were cultured in a high‑glucose in vitro environment, and the percentage of M1 macrophages in 138.8 mmol/l glucose medium significantly increased over time. The percentage of M2 macrophages increased in a glucose concentration‑dependent and time‑dependent manner. Arginase 1 in murine macrophages and the level of transforming growth factor β1 in the supernatant increased in a glucose concentration‑dependent manner. In conclusion, high glucose contributed to the polarization of peritoneal macrophages to the M2 phenotype, which may play an important role in the pathogenesis of PD‑related fibrosis.

Protein kinase C beta deficiency increases glucose-mediated peritoneal damage via M1 macrophage polarization and up-regulation of mesothelial protein kinase C alpha

BACKGROUND

Peritoneal membrane (PM) damage during peritoneal dialysis (PD) is mediated largely by high glucose (HG)-induced pro-inflammatory and neo-angiogenic processes, resulting in PM fibrosis and ultrafiltration failure. We recently demonstrated a crucial role for protein kinase C (PKC) isoform α in mesothelial cells.

METHODS

In this study we investigate the role of PKCβ in PM damage in vitro using primary mouse peritoneal macrophages (MPMΦ), human macrophages (HMΦ) and immortalized mouse peritoneal mesothelial cells (MPMCs), as well as in vivo using a chronic PD mouse model.

RESULTS

We demonstrate that PKCβ is the predominant classical PKC isoform expressed in primary MPMΦ and its expression is up-regulated in vitro under HG conditions. After in vitro lipopolysaccharides stimulation PKCβ-/- MPMΦ demonstrates increased levels of interleukin 6 (IL-6), tumour necrosis factor α, and monocyte chemoattractant protein-1 and drastically decrease IL-10 release compared with wild-type (WT) cells. In vivo, catheter-delivered treatment with HG PD fluid for 5 weeks induces PKCβ up-regulation in omentum of WT mice and results in inflammatory response and PM damage characterized by fibrosis and neo-angiogenesis. In comparison to WT mice, all pathological changes are strongly aggravated in PKCβ-/- animals. Underlying molecular mechanisms involve a pro-inflammatory M1 polarization shift of MPMΦ and up-regulation of PKCα in MPMCs of PKCβ-/- mice. Finally, we demonstrate PKCβ involvement in HG-induced polarization processes in HMΦ.

CONCLUSIONS

PKCβ as the dominant PKC isoform in MPMΦ is up-regulated by HG PD fluid and exerts anti-inflammatory effects during PD through regulation of MPMΦ M1/M2 polarization and control of the dominant mesothelial PKC isoform α.

Inflammatory macrophages switch to CCL17-expressing phenotype and promote peritoneal fibrosis

Peritoneal fibrosis remains a problem in kidney failure patients treated with peritoneal dialysis. Severe peritoneal fibrosis with encapsulation or encapsulating peritoneal sclerosis is devastating and life-threatening. Although submesothelial fibroblasts as the major precursor of scar-producing myofibroblasts in animal models and M2 macrophage (Mϕ)-derived chemokines in peritoneal effluents of patients before diagnosis of encapsulating peritoneal sclerosis have been identified, attenuation of peritoneal fibrosis is an unmet medical need partly because the mechanism for cross talk between Mϕs and fibroblasts remains unclear. We use a sodium hypochlorite-induced mouse model akin to clinical encapsulated peritoneal sclerosis to study how the peritoneal Mϕs activate fibroblasts and fibrosis. Sodium hypochlorite induces the disappearance of CD11b^high F4/80^high resident Mϕs but accumulation of CD11b^int F4/80^int inflammatory Mϕs (InfMϕs) through recruiting blood monocytes and activating local cell proliferation. InfMϕs switch to express chemokine (C-C motif) ligand 17 (CCL17), CCL22, and arginase-1 from day 2 after hypochlorite injury. More than 75% of InfMϕs undergo genetic recombination by Csf1r-driven Cre recombinase, providing the possibility to reduce myofibroblasts and fibrosis by diphtheria toxin-induced Mϕ ablation from day 2 after injury. Furthermore, administration of antibody against CCL17 can reduce Mϕs, myofibroblasts, fibrosis, and improve peritoneal function after injury. Mechanistically, CCL17 stimulates migration and collagen production of submesothelial fibroblasts in culture. By breeding mice that are induced to express red fluorescent protein in Mϕs and green fluorescence protein (GFP) in Col1a1-expressing cells, we confirmed that Mϕs do not produce collagen in peritoneum before and after injury. However, small numbers of fibrocytes are found in fibrotic peritoneum of chimeric mice with bone marrow from Col1a1-GFP reporter mice, but they do not contribute to myofibroblasts. These data demonstrate that InfMϕs switch to pro-fibrotic phenotype and activate peritoneal fibroblasts through CCL17 after injury. CCL17 blockade in patients with peritoneal fibrosis may provide a novel therapy. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Differences in peritoneal response after exposure to low-GDP bicarbonate/lactate-buffered dialysis solution compared to conventional dialysis solution in a uremic mouse model

Background

Long-term exposure of conventional peritoneal dialysis (PD) fluid is associated with structural membrane alterations and technique failure. Previously, it has been shown that infiltrating IL-17-secreting CD4+T cells and pro-fibrotic M2 macrophages play a critical role in the PD-induced pathogenesis. Although more biocompatible PD solutions are recognized to better preserve the peritoneal membrane integrity, the impact of these fluids on the composition of the peritoneal cell infiltrate is unknown.

Materials and methods

In a uremic PD mouse model, we compared the effects of daily instillation of standard lactate (LS) or bicarbonate/lactate-buffered solutions (BLS) and respective controls on peritoneal fibrosis, vascularisation, and inflammation.

Results

Daily exposure of LS fluid during a period of 8 weeks resulted in a peritoneal increase of αSMA and collagen accompanied with new vessel formation compared to the BLS group. Effluent from LS-treated mouse showed a higher percentage of CD4⁺ IL-17⁺ cell population while BLS exposure resulted in an increased macrophage population. Significantly enhanced inflammatory cytokines such as TGFβ1, TNFα, INFγ, and MIP-1β were detected in the effluent of BLS-exposed mice when compared to other groups. Further, immunohistochemistry of macrophage subset infiltrates in the BLS group confirmed a higher ratio of pro-inflammatory M1 macrophages over the pro-fibrotic M2 subset compared to LS.

Conclusion

Development of the peritoneal fibrosis and angiogenesis was prevented in the BLS-exposed mice, which may underlie its improved biocompatibility. Peritoneal recruitment of M1 macrophages and lower number of CD4⁺ IL-17⁺ cells might explain the peritoneal integrity preservation observed in BLS-exposed mouse.

Encapsulating Peritoneal Sclerosis

Encapsulating peritoneal sclerosis (EPS) is a rare but serious complication of peritoneal dialysis. In this review, we describe the clinical picture and histologic changes to the peritoneal membrane that are associated with EPS and provide an update on current diagnosis and management. We also discuss the recent studies that have suggested that the use of more biocompatible solutions containing lower concentrations of glucose degradation product that often are pH neutral in combination with a change in clinical practice (reducing glucose exposure and monitoring peritoneal membrane function) might ameliorate peritoneal degeneration, reduce the incidence of EPS, and minimize the severity of the disease.

Sustained low peritoneal effluent CCL18 levels are associated with preservation of peritoneal membrane function in peritoneal dialysis

Peritoneal membrane failure (PMF) and, ultimately, encapsulating peritoneal sclerosis (EPS) are the most serious peritoneal dialysis (PD) complications. Combining clinical and peritoneal transport data with the measurement of molecular biomarkers, such as the chemokine CCL18, would improve the complex diagnosis and management of PMF. We measured CCL18 levels in 43 patients’ effluent and serum at baseline and after 1, 2, and 3 years of PD treatment by retrospective longitudinal study, and evaluated their association with PMF/EPS development and peritoneal risk factors. To confirm the trends observed in the longitudinal study, a cross-sectional study was performed on 61 isolated samples from long-term (more than 3 years) patients treated with PD. We observed that the patients with no membrane dysfunction showed sustained low CCL18 levels in peritoneal effluent over time. An increase in CCL18 levels at any time was predictive of PMF development (final CCL18 increase over baseline, p = .014; and maximum CCL18 increase, p = .039). At year 3 of PD, CCL18 values in effluent under 3.15 ng/ml showed an 89.5% negative predictive value, and higher levels were associated with later PMF (odds ratio 4.3; 95% CI 0.90–20.89; p = .067). Moreover, CCL18 levels in effluent at year 3 of PD were independently associated with a risk of PMF development, adjusted for the classical (water and creatinine) peritoneal transport parameters. These trends were confirmed in a cross-sectional study of 61 long-term patients treated with PD. In conclusion, our study shows the diagnostic capacity of chemokine CCL18 levels in peritoneal effluent to predict PMF and suggests CCL18 as a new marker and mediator of this serious condition as well as a new potential therapeutic target.

Abatacept as a therapeutic option in the treatment of encapsulated peritoneal sclerosis: an experimental rat model

PURPOSE

Encapsulated peritoneal sclerosis (EPS) is a rare complication of long-term peritoneal dialysis (PD) and is usually associated with mortality. Inflammation is a leading factor for developing EPS. This study aimed to investigate the effect of abatacept on peritoneal fibrosis and inflammation using the EPS rat model.

METHODS

Twenty-four Wistar albino rats were randomly divided into four equal groups. Group I (control group) was administered isotonic saline (IS) via the intraperitoneal (ip) route during weeks 0-3. Chlorhexidine gluconate (CG) ip was administered to group II (CG group) during weeks 0-3. Group III (CG + IS group) received CG for the first 21 days and IS solution for the following 3 weeks. Group IV (abatacept group) received CG during weeks 0-3, and subsequently, 50 mcg/day abatacept during weeks 4-6. Peritoneal thickness, fibrosis, and inflammation were examined using light microscopy. Expressions of matrix metalloproteinase-2 (MMP-2) and transforming growth factor-beta 1 (TGF-β1) were detected by immunohistochemical staining.

RESULTS

Lesser peritoneal thickness and lower inflammation score were observed in the abatacept group than in the CG and CG + IS groups (p < 0.05). Furthermore, the abatacept group had a lower fibrosis score than the CG + IS group (p < 0.05). MMP-2 and TGF-β1 scores were lower in the abatacept group than in the CG + IS group (p < 0.05).

CONCLUSIONS

The results revealed that abatacept had a histopathological beneficial effect on peritoneal fibrosis, inflammation, MMP-2, and TGF-β1 scores, which were induced by CG. Abatacept could be a new therapeutic option for treating EPS.

Preventing peritoneal membrane fibrosis in peritoneal dialysis patients

Long-term peritoneal dialysis causes morphologic and functional changes in the peritoneal membrane. Although mesothelial-mesenchymal transition of peritoneal mesothelial cells is a key process leading to peritoneal fibrosis, and bioincompatible peritoneal dialysis solutions (glucose, glucose degradation products, and advanced glycation end products or a combination) are responsible for altering mesothelial cell function and proliferation, mechanisms underlying these processes remain largely unclear. Peritoneal fibrosis has 2 cooperative parts, the fibrosis process itself and the inflammation. The link between these 2 processes is frequently bidirectional, with each one inducing the other. This review outlines our current understanding about the definition and pathophysiology of peritoneal fibrosis, recent studies on key fibrogenic molecular machinery in peritoneal fibrosis, such as the role of transforming growth factor-β/Smads, transforming growth factor-β β/Smad independent pathways, and noncoding RNAs. The diagnosis of peritoneal fibrosis, including effluent biomarkers and the histopathology of a peritoneal biopsy, which is the gold standard for demonstrating peritoneal fibrosis, is introduced in detail. Several interventions for peritoneal fibrosis based on biomarkers, cytology, histology, functional studies, and antagonists are presented in this review. Recent experimental trials in animal models, including pharmacology and gene therapy, which could offer novel insights into the treatment of peritoneal fibrosis in the near future, are also discussed in depth.