Aurélie Philippe

Involvement of functional autoantibodies against vascular receptors in systemic sclerosis

Background Systemic sclerosis (SSc) features autoimmunity, vasculopathy and tissue fibrosis. The renin-angiotensin and endothelin systems have been implicated in vasculopathy and fibrosis. A role for autoantibody-mediated receptor stimulation is hypothesised, linking three major pathophysiological features consistent with SSc. Methods Serum samples from 478 patients with SSc (298 in the study cohort and 180 from two further independent cohorts), 372 healthy subjects and 311 control-disease subjects were tested for antibodies against angiotensin II type 1 receptor (AT1R) and endothelin-1 type A receptor (ETAR) by solid phase assay. Binding specificities were tested by immunoprecipitation. The biological effects of autoantibodies in microvascular endothelial cells in vitro were also determined, as well as the quantitative differences in autoantibody levels on specific organ involvements and their predictive value for SSc-related mortality. Results Anti-AT1R and anti-ETAR autoantibodies were detected in most patients with SSc. Autoantibodies specifically bound to respective receptors on endothelial cells. Higher levels of both autoantibodies were associated with more severe disease manifestations and predicted SSc-related mortality. Both autoantibodies exert biological effects as they induced extracellular signal-regulated kinase 1/2 phosphorylation and increased transforming growth factor β gene expression in endothelial cells which could be blocked with specific receptor antagonists. Conclusions Functional autoimmunity directed at AT1R and ETAR is common in patients with SSc. AT1R and ETAR autoantibodies could contribute to disease pathogenesis and may serve as biomarkers for risk assessment of disease progression.

Pretransplant Sensitization Against Angiotensin II Type 1 Receptor Is a Risk Factor for Acute Rejection and Graft Loss

The angiotensin II type 1 receptor (AT1R) is an emerging target of functional non‐HLA antibodies (Ab). We examined the potential of determining the degree of presensitization against AT1R as a risk factor for graft survival and acute rejection (AR). The study included 599 kidney recipients between 1998 and 2007. Serum samples were analyzed in a blinded fashion for anti‐AT1R antibodies (AT1R‐Abs) using a quantitative solid‐phase assay. A threshold of AT1R‐Ab levels was statistically determined at 10 U based on the time to graft failure. An extended Cox model determined risk factors for occurrence of graft failure and a first AR episode. AT1R‐Abs >10 U were detected in 283 patients (47.2%) before transplantation. Patients who had a level of AT1R‐Abs >10 U had a 2.6‐fold higher risk of graft failure from 3 years posttransplantation onwards (p = 0.0005) and a 1.9‐fold higher risk of experiencing an AR episode within the first 4 months of transplantation (p = 0.0393). Antibody‐mediated rejection (AMR) accounted for 1/3 of AR, whereby 71.4% of them were associated with >10 U of pretransplant AT1R‐Abs. Pretransplant anti‐AT1R‐Abs are an independent risk factor for long‐term graft loss in association with a higher risk of early AR episodes.

Non-HLA antibodies in solid organ transplantation: recent concepts and clinical relevance.

Purpose of review Humoral responses beyond major histocompatibility antigens continue to receive the attention of the transplantation community. We report on clinical studies testing clinical relevance of non-human leukocyte antigen (HLA) antigens in solid organ transplantation and provide an update on novel experimental findings. A conceptual framework on the role of graft microenvironment during initiation of non-HLA-related humoral immunity is addressed as well. Recent findings Clinical relevance of antibodies targeting angiotensin type 1 receptor (AT1R-Abs) is broadly confirmed in renal and cardiac transplantation, where in addition antibodies against endothelin type A receptor (ETAR-Abs) were found. Obliterative lesions in lung allografts occur more commonly in the presence of antibodies directed against K-&agr; 1 tubulin and collagen-V. Anti-perlecan antibodies are newly identified as accelerators of obliterative vascular lesions. Changes in the intragraft microenvironment, ischemia and alloimmunity seem to represent important permissive factors for non-HLA antibody responses. Summary Confirmed clinical relevance of non-HLA humoral responses in solid organ transplantation emphasizes the need for revision of classical diagnostic approaches based solely on detection of HLA-donor-specific antibodies (DSA). A better understanding of intersections of HLA- and non-HLA-related mechanisms and identification of common effector mechanisms would represent an important step towards targeted therapies.

Role of non-HLA antibodies in organ transplantation.

Purpose of reviewHumoral responses beyond major histocompatibility antigens receive an increased attention of the transplantation community. We aimed to summarize the data on discovery of new antigenic targets, novel experimental findings, recent diagnostic developments, and introduction of new technologies in the field of non-HLA antigens in solid organ transplantation. Recent findingsNon-HLA antibodies can be currently reliably detected by solid-phase assays (MICA, angiotensin type 1 receptor, collagen-V, vimentin), immunofluorescence (antibodies against antigens expressed on umbilical vein endothelial cells), or flow-crossmatch techniques (antibodies against donor endothelial progenitors). Influence of test positivity on transplant outcomes is variable and differs among non-HLA targets. Use of omics approach helped to identify a unique set of antigens in adult and pediatric patients with severe rejections and transplant glomerulopathy. SummaryParadigms for effective monitoring of non-HLA humoral responses need to be established in order to utilize advances provided by the rapid diagnostic developments. A systematic longitudinal assessment of pretransplant sensitization together with monitoring of posttransplant changes would represent an important step forward.

Non-HLA-antibodies targeting Angiotensin type 1 receptor and antibody mediated rejection.

Antibody-mediated mechanisms directed against non-HLA related targets may exert negative impact on allograft function and survival. Angiotensin type 1 receptor (AT(1)R) emerges as a functional target for non-HLA allo- and autoantibodies (AT(1)R-Abs) comprising of IgG1 and IgG3 subclasses. Proof of concept for pathophysiologic relevance of AT(1)R-Abs in antibody mediated rejection (AMR) in renal transplants was provided by passive transfer studies in animal model and therapeutic rescue of patients. Although AT(1)R-Abs may belong to complement fixing IgG subclasses, C4d positivity in renal transplant biopsies was not frequently detected implicating complement independent mechanisms of injury. AT(1)R-Abs exert direct effects on endothelial and vascular smooth muscle cells by induction of Erk1/2 signaling and increased DNA binding of transcription factors associated with pro-inflammatory and pro-coagulatory responses. Establishment of enzyme-linked immunosorbent assay employing extracts of cells overexpressing AT(1)R in its native conformation was instrumental for recent studies in independent cohorts. Assessing the AT(1)R-Ab-status along with the HLA-antibodies may help to identify patients at particular risk for irreversible acute or chronic allograft injuries and improve overall outcomes. This review summarizes the current state of research in AT(1)R biology, development in diagnostic strategies, discusses recent clinical studies, and provides perspectives on further refinements in understanding AT(1)R-Ab-actions.

Autoimmune mediated G-protein receptor activation in cardiovascular and renal pathologies

Antibodies directed against G-protein coupled receptors (GPCR) can act as allosteric receptor agonists or antagonists. Prototypic disease for agonistic antibody action is a Graves disease of the thyroid gland where antibodies that stimulate G-protein coupled thyroid-stimulating hormone receptor (TSHR) were first described 50 years ago. Myasthenia gravis is the prototype for antagonistic autoimmune actions, where antibodies directed against the nicotinic acetylcholine receptor (AChR) cause blockade of neuromuscular junctions. Antibodies and B-cells are increasingly recognised as major modulators of various cardiovascular and renal pathologies. We aim to critically review the notion that antibodies targeting other GPCRs may amplify or cause various cardiovascular and renal pathologies and summarise the current state of research, as well as perspectives in diagnostic and therapeutic strategies. In terms of targets we will focus on the alpha-adrenergic receptor (alpha(1)AR), the beta-adrenergic receptor (beta(1)AR), and the angiotensin II type 1 receptor (AT(1)R).

The proto-oncogene c-Fos transcriptionally regulates VEGF production during peritoneal inflammation

Vascular endothelial growth factor (VEGF) and transforming growth factor-β1 (TGF-β1) are key mediators of adverse peritoneal membrane remodeling in peritoneal dialysis eventually leading to ultrafiltration failure. Both are pleiotropic growth factors with cell type-dependent regulation of expression and biological effects. Here we studied regulation of TGF-β1-induced VEGF expression in human peritoneal mesothelial cells in the absence or presence of proinflammatory stimuli, tumor necrosis factor-α (TNF-α) or interleukin-1β (IL-1β). Quiescent human peritoneal mesothelial cells secreted only trace amounts of VEGF. Stimulation with TGF-β1 resulted in time- and dose-dependent increases in VEGF mRNA expression and protein release. TNF-α and IL-1β alone had minimal effects but acted in synergy with TGF-β1. Combined stimulation led to induction of transcription factor c-Fos and activation of the VEGF promoter region with high-affinity binding sites for c-Fos. Inhibition of c-Fos by small interfering RNA interference or by pharmacological blockade with SR-11302 decreased VEGF promoter activity and downregulated its expression and release. Exposure of human peritoneal mesothelial cells to dialysate effluent containing increased levels of TGF-β1, TNF-α, and IL-1β obtained during peritonitis resulted in a dose-dependent VEGF induction that was significantly attenuated by SR-11302. Thus, dialysate TGF-β1, IL-1β, and TNF-α act through c-Fos to synergistically upregulate VEGF production in peritoneal mesothelium and may represent an important regulatory link between inflammation and angiogenesis in the peritoneal membrane.

Renal Ischemia/Reperfusion Injury in Soluble Epoxide Hydrolase-Deficient Mice

Aim 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) are cytochrome P450 (CYP)-dependent eicosanoids that play opposite roles in the regulation of vascular tone, inflammation, and apoptosis. 20-HETE aggravates, whereas EETs ameliorate ischemia/reperfusion (I/R)-induced organ damage. EETs are rapidly metabolized to dihydroxyeicosatrienoic acids (DHETs) by the soluble epoxide hydrolase (sEH). We hypothesized that sEH gene (EPHX2) deletion would increase endogenous EET levels and thereby protect against I/R-induced acute kidney injury (AKI). Methods Kidney damage was evaluated in male wildtype (WT) and sEH-knockout (KO)-mice that underwent 22-min renal ischemia followed by two days of reperfusion. CYP-eicosanoids were analyzed by liquid chromatography tandem mass spectrometry. Results Contrary to our initial hypothesis, renal function declined more severely in sEH-KO mice as indicated by higher serum creatinine and urea levels. The sEH-KO-mice also featured stronger tubular lesion scores, tubular apoptosis, and inflammatory cell infiltration. Plasma and renal EET/DHET-ratios were higher in sEH-KO than WT mice, thus confirming the expected metabolic consequences of sEH deficiency. However, CYP-eicosanoid profiling also revealed that renal, but not plasma and hepatic, 20-HETE levels were significantly increased in sEH-KO compared to WT mice. In line with this finding, renal expression of Cyp4a12a, the murine 20-HETE-generating CYP-enzyme, was up-regulated both at the mRNA and protein level, and Cyp4a12a immunostaining was more intense in the renal arterioles of sEH-KO compared with WT mice. Conclusion These results indicate that the potential beneficial effects of reducing EET degradation were obliterated by a thus far unknown mechanism leading to kidney-specific up-regulation of 20-HETE formation in sEH-KO-mice.

Non-HLA Antibodies Impact on C4d Staining, Stellate Cell Activation and Fibrosis in Liver Allografts

Background Recent data have shown an increased risk for rejection, fibrosis progression, and death in liver transplantation (LT) recipients with preformed or de novo HLA donor-specific alloantibodies (DSA). However, the role of non-HLA autoantibodies and the interaction between HLA DSA and non-HLA autoantibodies remains uncharacterized. Methods We analyzed 1269 primary LT recipients from 1 of 2000 to 4 of 2009 with known HLA DSA status for angiotensin II type-1 receptor and endothelin-1 type A receptor autoantibodies pre-LT, and year 1 post-LT. Results Preformed non-HLA autoantibodies alone did not impact outcomes. In multivariable modeling, the combination of preformed non-HLA autoantibodies and HLA-DSA were associated with an increased risk for death (hazard ratio [HR], 1.66; P = 0.02) especially if the HLA DSA was of the IgG3 subclass (HR, 2.28; P = 0.01). A single de novo non-HLA autoantibody was associated with an increased risk for T cell–mediated rejection or antibody-mediated rejection (68% vs 41%, P = 0.01) and fibrosis progression (HR, 1.84; P = 0.02). Biopsies with de novo non-HLA autoantibodies revealed a new sinusoidal C4d staining pattern when compared with HLA DSA (71% vs 3%; P < 0.001). Liver sinusoidal endothelial cell activation and stellate cell activation was increased in patients with non-HLA autoantibodies in the location of C4d positivity. Conclusions A non-HLA autoantibody combined with a preformed HLA DSA is associated with an increased mortality risk. Isolated de novo anti-angiotensin II type-1 receptor and anti-endothelin-1 type A receptor autoantibodies are associated with an increased risk of rejection and fibrosis progression. The novel location of C4d staining in proximity to liver sinusoidal endothelial cell capillarization and stellate cell activation demonstrates allograft injury in proximity to non-HLA autoantibody binding.

Antibodies against chemokine receptors CXCR3 and CXCR4 predict progressive deterioration of lung function in patients with systemic sclerosis

BackgroundThe chemokine receptors CXCR3 and CXCR4 are involved in the pathogenesis of fibrosis, a key feature of systemic sclerosis (SSc). It is hypothesized that immunoglobulin (Ig)G antibodies (abs) against these two receptors are present in patients with SSc and are associated with clinical findings.MethodsAnti-CXCR3 and anti-CXCR4 ab levels were measured in 449 sera from 327 SSc patients and in 234 sera from healthy donors (HD) by enzyme-linked immunosorbent assay (ELISA). In SSc, ab levels were compared with clinical data in a cross-sectional and longitudinal setting. Protein expression of CXCR3 and CXCR4 on peripheral blood mononuclear cells (PBMCs) was analyzed in 17 SSc patients and 8 HD by flow cytometry.ResultsAnti-CXCR3 and anti-CXCR4 ab levels were different among SSc subgroups compared with HD and were highest in diffuse SSc patients. The ab levels strongly correlated with each other (r = 0.85). Patients with SSc-related interstitial lung disease (SSc-ILD) exhibited higher ab levels which negatively correlated with lung function parameters (e.g., r = −0.5 and r = −0.43 for predicted vital capacity, respectively). However, patients with deterioration of lung function showed lower anti-CXCR3/4 ab levels compared with those with stable disease. Frequencies and median fluorescence intensities (MFI) of CXCR3+ and CXCR4+ PBMCs were lower in SSc patients compared with HD and correlated with the severity of skin and lung fibrosis. They correlated with the severity of skin and lung fibrosis.ConclusionsAnti-CXCR3/4 abs and their corresponding receptors are linked with the severity of SSc-ILD. Antibody levels discriminate patients with stable or decreasing lung function and could be used for risk stratification.