Vascular Receptor Autoantibodies in Pulmonary Arterial Hypertension Associated with Systemic Sclerosis

Kidney involvement in systemic sclerosis: From pathogenesis to treatment

Among all possible systemic sclerosis internal organ complications, kidney involvement is frequently neglected or underestimated, except for the life-threatening scleroderma renal crisis. Fortunately, this severe clinical presentation is nowadays better controlled with available treatments, in particular angiotensin-converting enzyme inhibitors, and this has led to a reduction in its short- and longer-term mortality. Pathogenetic determinants are not well understood and many different other kidney involvements are possible in systemic sclerosis, including proteinuria, albuminuria, reduction of renal filtration, autoantibodies-related glomerulonephritis, and drug-related side effects. Different serological and radiological methods of evaluations are nowadays available, some representing promising diagnostic tool and prognostic outcome measure. Except for angiotensin-converting enzyme inhibitors in scleroderma renal crisis, no other treatment is currently recommended for treatment of kidney involvement in systemic sclerosis. For this reason, further studies are necessary to investigate its prognostic impact, in particular in combination with other systemic sclerosis-related internal organ manifestations. This review summarizes current available literature on kidney involvement in systemic sclerosis.

Pulmonary arterial hypertension in the setting of scleroderma is different than in the setting of lupus: A review

Pulmonary hypertension (PH) is a clinical syndrome that is subdivided into five groups per the World Health Organization (WHO) classification, based largely on hemodynamic and pathophysiologic criteria. WHO Group 1 PH, termed pulmonary arterial hypertension (PAH), is a clinically progressive disease that can eventually lead to right heart failure and death, and it is hemodynamically characterized by pre-capillary PH and increased pulmonary vascular resistance in the absence of elevated left ventricular filling pressures. PAH can be idiopathic, heritable, or associated with a variety of conditions. Connective tissue diseases make up the largest portion of these associated conditions, most commonly systemic sclerosis (SSc), followed by mixed connective tissue disease and systemic lupus erythematous. These etiologies (namely SSc and Lupus) have been grouped together as connective tissue disease-associated PAH, however emerging evidence suggests they differ in pathogenesis, clinical course, prognosis, and treatment response. This review highlights the differences between SSc-PAH and Lupus-PAH. After introducing the diagnosis, screening, and pathobiology of PAH, we discuss connective tissue disease-associated PAH as a group, and then explore SSc-PAH and SLE-PAH separately, comparing these 2 PAH etiologies.

Immune cells and autoantibodies in pulmonary arterial hypertension

Analyses of immunity in pulmonary arterial hypertension (PAH) support the notion that maladaptation of the immune response exists. Altered immunity is an increasingly recognized feature of PAH. Indeed, a delicate balance between immunity and tolerance exists and any disturbance may result in chronic inflammation or autoimmunity. This is suggested by infiltration of various immune cells (e.g. macrophages, T and B lymphocytes) in remodeled pulmonary vessels. In addition, several types of autoantibodies directed against antinuclear antigens, endothelial cells (ECs) and fibroblasts have been found in idiopathic and systemic sclerosis-associated PAH. These autoantibodies may play an important role in EC apoptosis and in the expression of cell adhesion molecules. This review article provides an overview of immunity pathways highlighting their potential roles in pulmonary vascular remodeling in PAH and the possibility of future targeted therapy.

Agonistic antibodies in systemic sclerosis

Systemic sclerosis (SSc) is characterized by microangiopathy, excessive fibrosis, and the presence of circulating autoantibodies to several cellular and extracellular components. The role of autoimmunity in generating the clinical and pathologic phenotypes in SSc has been long debated and is still matter of controversy. Distinct specificities of antinuclear antibodies (ANAs) are selectively detected in SSc patients and are associated with unique disease manifestations, but do not have a proven pathogenic role. A new group of autoantibodies reactive with cell surface receptors have been identified in SSc patients. They have been shown to directly activate pathways that may contribute to tissue and vascular damage. As such, they are proposed to have a role as agonistic autoantibodies in SSc. According to Koch's third postulate, the autoantibodies in question should cause disease when introduced into a healthy subject. Therefore, our review will focus on those autoantibodies for which agonistic activity has already been demonstrated not only in vitro, but, at least partly, also in vivo. These include the antibodies anti-endothelial cells (AECA), anti-Platelet-Derived Growth Factor Receptor (PDGFR), anti-Angiotensin II type 1 receptor (AT1R) and anti-endothelin-1 type A receptor (ETaR). In this review, we will discuss also a class of antagonistic autoantibodies, the anti-muscarinic-3 receptor (M3R) antibodies, since they seem to fulfill the aforementioned requirements.

Functional autoantibodies targeting G protein-coupled receptors in rheumatic diseases

G protein-coupled receptors (GPCRs) comprise the largest and most diverse family of integral membrane proteins that participate in different physiological processes such as the regulation of the nervous and immune systems. Besides the endogenous ligands of GPCRs, functional autoantibodies are also able to bind GPCRs to trigger or block intracellular signalling pathways, resulting in agonistic or antagonistic effects, respectively. In this Review, the effects of functional GPCR-targeting autoantibodies on the pathogenesis of autoimmune diseases, including rheumatic diseases, are discussed. Autoantibodies targeting β1 and β2 adrenergic receptors, which are expressed by cardiac and airway smooth muscle cells, respectively, have an important role in the development of asthma and cardiovascular diseases. In addition, high levels of autoantibodies against the muscarinic acetylcholine receptor M3 as well as those targeting endothelin receptor type A and type 1 angiotensin II receptor have several implications in the pathogenesis of rheumatic diseases such as Sjögren syndrome and systemic sclerosis. Expanding the knowledge of the pathophysiological roles of autoantibodies against GPCRs will shed light on the biology of these receptors and open avenues for new therapeutic approaches.

Inflammation, Autoimmunity, and Hypertension: The Essential Role of Tissue Transglutaminase

Inflammatory cytokines cause hypertension when introduced into animals. Additional evidence indicates that cytokines induce the production of autoantibodies that activate the AT1 angiotensin receptor (AT1R). Extensive evidence shows that these autoantibodies, termed AT1-AA, contribute to hypertension. We review here recent studies showing that cytokine-induced hypertension and AT1-AA production require the ubiquitous enzyme, tissue transglutaminase (TG2). We consider 3 mechanisms by which TG2 may contribute to hypertension. (i) One involves the posttranslational modification (PTM) of AT1Rs at a glutamine residue that is present in the epitope sequence (AFHYESQ) recognized by AT1-AA. (ii) Another mechanism by which TG2 may contribute to hypertension is by PTM of AT1Rs at glutamine 315. Modification at this glutamine prevents ubiquitination-dependent proteasome degradation and allows AT1Rs to accumulate. Increased AT1R abundance is likely to account for increased sensitivity to Ang II activation and in this way contribute to hypertension. (iii) The increased TG2 produced as a result of elevated inflammatory cytokines is likely to contribute to vascular stiffness by modification of intracellular contractile proteins or by crosslinking vascular proteins in the extracellular matrix. This process, termed inward remodeling, results in reduced vascular lumen, vascular stiffness, and increased blood pressure. Based on the literature reviewed here, we hypothesize that TG2 is an essential participant in cytokine-induced hypertension. From this perspective, selective TG2 inhibitors have the potential to be pharmacologic weapons in the fight against hypertension.

Role of anti-receptor autoantibodies in pathophysiology of scleroderma

The pathophysiology of SSc-mediated organ damage is complex and not well understood. Hallmarks of the disease include skin thickening, vasculopathy and gastrointestinal dysmotility. Diverse anti-nuclear antibodies can be used as biomarkers for classification and prognosis, but their role in producing tissue pathology/organ dysfunction is not established. In contrast, antibodies against cell surface receptors for platelet derived growth factor, angiotensin II, endothelin A, ICAM-1, and type 3 muscarinic acetyl choline receptors may play a major role in skin thickening, vasoconstriction/pulmonary and renal hypertension, ischemia and gastrointestinal dysmotility, respectively. In addition, antibodies to an inhibitory B-lymphocyte surface molecule, CD 22, may allow increased production of other autoantibodies. Each of these types of antibodies have been reported in some SSc patients, and laboratory studies suggest signaling pathways and mechanisms by which they may contribute to disease activity. However, we are far from a consensus on their importance. Additional epidemiologic, mechanistic and physiologic studies are needed. Confirmation of the roles of anti-receptor antibodies and identification of the signaling pathways by which they alter cellular functions would have major implications for treatment of SSc, both in terms of targeting autoantibodies and the cells that produce them, and in the use of small molecules which inhibit their pernicious effects.

Circulating angiotensin type II receptor: Possible marker for antibody mediated rejection after renal transplantation?

BACKGROUND

Presence of antibody [Ab] against angiotensin receptor [AT1R] indicates heightened risk for antibody mediated rejection [AMR] after transplantation but is insufficient as a marker. We speculated AT1R might be released systemically because of AMR and might be a useful biomarker.

METHODS

AT1R was measured in blood from 73 Normals and 72 renal patients pre- and post-transplantation. Patients were stratified as AMR-free [Gp1], AMR<1yr [Gp2] and AMR>1yr [Gp3].

RESULTS

AT1R was higher [13±26vs.367±537, p<0.01)] and more prevalent [20% vs. 92%, p<0.01] among renal patients than Normals. Pretransplant levels were similar [p=ns] between groups. One-year posttransplant levels approached [p<0.01] normalcy for Gps1+3 but spiked during AMR and remained elevated [155±58, p<0.01] for 50% Gp2 patients. One-year AT1R levels were higher among subsequent graft failures than surviving grafts [171±267vs. 38±50, p<0.01].

CONCLUSIONS

Pretransplant AT1R was abnormally elevated: possibly indicating ongoing tissue injury. Pretransplant AT1R didn't predict risk for AMR. However, AT1R spiked during early AMR and sustained elevations were associated with poorer outcomes.

Functional autoantibodies directed against cell surface receptors in systemic sclerosis

Systemic sclerosis (SSc) is a complex and heterogeneous systemic autoimmune disease characterized by the presence of high serum levels of antibodies targeting a variety of self-antigens. In addition to autoantibodies directed against nuclear antigens, patients with SSc also develop high serum levels of functional autoantibodies that target cell surface receptors when compared to healthy subjects. Following binding to extracellular receptors, these functional autoantibodies trigger the activation of signal transducing pathways, resulting in a stimulatory or suppressive effect. For example, stimulatory autoantibodies toward platelet-derived growth factor receptor (PDGFR) or antibodies targeting G protein–coupled receptors (e.g., angiotensin II receptor type 1 and endothelin receptor type A) have pleiotropic roles in the pathogenesis of SSc. High levels of these functional autoantibodies dysregulate the response of non-immune cells (e.g., fibroblasts and endothelial cells) as well as innate and adaptive immune cells, including myeloid cells and lymphocytes, respectively. Thus, the immunobiology of such autoantibodies clarifies why patients with SSc develop clinical features such as extensive fibrosis, vasculopathies and abnormal immune responses. Future interventions that modulate the natural production of functional autoantibodies that target cell surface receptors or neutralize such autoantibodies would be essential in reducing morbidity and mortality rates presented by SSc patients.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

The mast cell–B cell axis in lung vascular remodeling and pulmonary hypertension

Over past years, a critical role for the immune system and, in particular, for mast cells in the pathogenesis of pulmonary hypertension (PH) has emerged. However, the way in which mast cells promote PH is still poorly understood. Here, we investigated the mechanisms by which mast cells may contribute to PH, specifically focusing on the interaction between the innate and adaptive immune response and the role of B cells and autoimmunity. Experiments were performed in Sprague-Dawley rats and B cell-deficient JH-KO rats in the monocrotaline, Sugen/hypoxia, and the aortic banding model of PH. Hemodynamics, cell infiltration, IL-6 expression, and vascular remodeling were analyzed. Gene array analyses revealed constituents of immunoglobulins as most prominently regulated mast cell-dependent genes in the lung in experimental PH. IL-6 was shown to link mast cells to B cells, as 1) IL-6 was upregulated and colocalized with mast cells and was reduced by mast-cell stabilizers and 2) IL-6 or mast cell blockade reduced B cells in lungs of monocrotaline-treated rats. A functional role for B cells in PH was demonstrated in that either blocking B cells by an anti-CD20 antibody or B-cell deficiency in JH-KO rats attenuated right ventricular systolic pressure and vascular remodeling in experimental PH. We here identify a mast cell–B cell axis driven by IL-6 as a critical immune pathway in the pathophysiology of PH. Our results provide novel insights into the role of the immune system in PH, which may be therapeutically exploited by targeted immunotherapy.

Immediate and Catastrophic Antibody-Mediated Rejection in a Lung Transplant Recipient With Anti-Angiotensin II Receptor Type 1 and Anti-Endothelin-1 Receptor Type A Antibodies

Preexisting donor-specific anti-HLA antibodies (DSAs) have been associated with reduced survival of lung allografts. However, antibodies with specificities other than HLA may have a detrimental role on the lung transplant outcome. A young man with cystic fibrosis underwent lung transplantation with organs from a suitable deceased donor. At the time of transplantation, there were no anti-HLA DSAs. During surgery, the patient developed a severe and intractable pulmonary hypertension associated with right ventriular dysfunction, which required arteriovenous extracorporeal membrane oxygenation. After a brief period of clinical improvement, a rapid deterioration in hemodynamics led to the patient's death on postoperative day 5. Postmortem studies showed that lung specimens taken at the end of surgery were compatible with antibody-mediated rejection (AMR), while terminal samples evidenced diffuse capillaritis, blood extravasation, edema, and microthrombi, with foci of acute cellular rejection (A3). Immunological investigations demonstrated the presence of preexisting antibodies against the endothelin-1 receptor type A (ET_A R) and the angiotensin II receptor type 1 (AT₁ R), two of the most potent vasoconstrictors reported to date, whose levels slightly rose after transplantation. These data suggest that preexisting anti-ET_A R and anti-AT₁ R antibodies may have contributed to the onset of AMR and to the catastrophic clinical course of this patient.

Recent advances in managing systemic sclerosis

How the main components in systemic sclerosis—namely autoimmunity, vasculopathy, and fibrosis—fit together is still not sufficiently clear. However, vascular treatment options are well established, the body of evidence for the efficacy of immunomodulatory approaches is increasing, and now at least one hopeful substance that may directly interfere with fibrosis is being tested. Although we still wait for important breakthroughs, there is grounds for hope that better therapeutic options will be available in the near future.

Interstitial lung disease increases mortality in systemic sclerosis patients with pulmonary arterial hypertension without affecting hemodynamics and exercise capacity

Published data suggest that coexisting interstitial lung disease (ILD) has an impact on mortality in patients with systemic sclerosis (SSc) and pulmonary arterial hypertension (PAH), but there is scarce knowledge if this is reflected by hemodynamics, exercise capacity, autoantibody profile, or pulmonary function. In this partially retrospective study, 27 SSc-PAH patients were compared to 24 SSc-PAH patients with coexisting ILD respecting to survival, pulmonary function, hemodynamics, exercise capacity, and laboratory parameters. Survival was significantly worse in SSc-PAH-ILD patients than in SSc patients with isolated PAH (1, 5, and 10-year survival rates 86, 54, and 54% versus 96, 92, and 82%, p = 0.013). Compared to isolated SSc-PAH patients, patients with SSc-PAH-ILD revealed lower forced expiratory volume after 1 s (FEV1) values at the time of PAH diagnosis as well as 1 and 2 years later (p = 0.002) without significant decrease in the PAH course in both groups. At PAH diagnosis, diffusion capacity for carbon monoxide (DLCO) values were lower in the ILD-PAH group. Coexisting ILD was not associated with lower exercise capacity, different FEV1/forced vital capacity (FVC) ratio, higher WHO functional class, or reduced hemodynamics. Higher levels of antibodies against angiotensin and endothelin receptors predict mortality in all SSc-PAH patients but could not differentiate between PAH patients with and without ILD. Our study confirmed an impact of ILD on mortality in SSc-PAH patients. Pulmonary function parameters can be used to distinguish PAH from PAH-ILD. The higher mortality rate cannot be explained by differences in hemodynamics, exercise capacity, or autoantibody levels. Mechanisms of mortality remain to be studied.

Anti-angiotensin II type 1 receptor autoantibodies (AT1R-AAs) in patients with systemic sclerosis: lack of association with disease manifestations

Angiotensin II type 1 receptor autoantibodies (AT₁R-AAs) are known to be associated with malignant hypertension, preeclampsia, and vascular rejection in kidney transplantation. They were also suspected to have pathogenetic role in vasculopathic changes in systemic sclerosis (SSc). Clinical data regarding AT₁R-AAs in SSc are scarce. In this work, we will examine the relationship between serum levels of AT₁R-AAs and disease manifestations. Serum samples from SSc patients and healthy controls were analyzed for AT₁R-AAs by using a commercial ELISA kit. We examined the association of serum levels of AT₁R-AA with disease duration, systolic pulmonary artery pressure (sPAP) measurements, and disease manifestations like cutaneous, lung and esophageal involvements, and the presence of digital ulcers in a cross-sectional manner. There was no statistically significant difference in levels of AT₁R-AAs between SSc (n = 93) patients and healthy controls (n = 66) (p = 0.23). Serum levels of AT₁R-AAs were not correlated with disease duration, sPAP measurements, and showed no association with disease manifestations like lung involvement, esophageal involvement, digital ulcers, and cutaneous fibrosis. In our SSc cohort, AT₁R-AA serum levels were not different from healthy subjects and higher levels were not associated with any disease manifestation neither.

Anti-LG3 Antibodies Aggravate Renal Ischemia-Reperfusion Injury and Long-Term Renal Allograft Dysfunction

Pretransplant autoantibodies to LG3 and angiotensin II type 1 receptors (AT1R) are associated with acute rejection in kidney transplant recipients, whereas antivimentin autoantibodies participate in heart transplant rejection. Ischemia-reperfusion injury (IRI) can modify self-antigenic targets. We hypothesized that ischemia-reperfusion creates permissive conditions for autoantibodies to interact with their antigenic targets and leads to enhanced renal damage and dysfunction. In 172 kidney transplant recipients, we found that pretransplant anti-LG3 antibodies were associated with an increased risk of delayed graft function (DGF). Pretransplant anti-LG3 antibodies are inversely associated with graft function at 1 year after transplantation in patients who experienced DGF, independent of rejection. Pretransplant anti-AT1R and antivimentin were not associated with DGF or its functional outcome. In a model of renal IRI in mice, passive transfer of anti-LG3 IgG led to enhanced dysfunction and microvascular injury compared with passive transfer with control IgG. Passive transfer of anti-LG3 antibodies also favored intrarenal microvascular complement activation, microvascular rarefaction and fibrosis after IRI. Our results suggest that anti-LG3 antibodies are novel aggravating factors for renal IRI. These results provide novel insights into the pathways that modulate the severity of renal injury at the time of transplantation and their impact on long-term outcomes.

The Emerging Importance of Non-HLA Autoantibodies in Kidney Transplant Complications

Antibodies that are specific to organ donor HLA have been involved in the majority of cases of antibody-mediated rejection in solid organ transplant recipients. However, recent data show that production of non-HLA autoantibodies can occur before transplant in the form of natural autoantibodies. In contrast to HLAs, which are constitutively expressed on the cell surface of the allograft endothelium, autoantigens are usually cryptic. Tissue damage associated with ischemia-reperfusion, vascular injury, and/or rejection creates permissive conditions for the expression of cryptic autoantigens, allowing these autoantibodies to bind antigenic targets and further enhance vascular inflammation and renal dysfunction. Antiperlecan/LG3 antibodies and antiangiotensin II type 1 receptor antibodies have been found before transplant in patients with de novo transplants and portend negative long-term outcome in patients with renal transplants. Here, we review mounting evidence suggesting an important role for autoantibodies to cryptic antigens as novel accelerators of kidney dysfunction and acute or chronic allograft rejection.

Current Approaches to the Treatment of Systemic-Sclerosis-Associated Pulmonary Arterial Hypertension (SSc-PAH)

Pulmonary arterial hypertension (PAH) is a severe condition causing significant morbidity and mortality in patients with systemic sclerosis (SSc). Despite the use of specific treatments, SSc-PAH survival remains poorer than in idiopathic PAH (IPAH). Recent therapeutic advances in PAH show a lower magnitude of response in SSc-PAH and a higher risk of adverse events, as compared to IPAH. The multifaceted underlying mechanisms and the multisystem nature of SSc probably explain part of the worse outcomes in SSc-PAH compared to IPAH. This review describes the current management of SSc-PAH with an emphasis on the impact of the different organ involvements in the prognosis and treatment response. An earlier detection of PAH and a better characterization of the clinical phenotypes of SSc-PAH are warranted in clinical practice and future trials. Determinants of prognosis, surrogate markers of clinical improvement or worsening, and relevance of the common endpoints used in clinical trials should be evaluated in this specific population. A multidisciplinary approach in expert referral centers is mandatory for SSc-PAH management.

Recent Developments in the Classification, Evaluation, Pathophysiology, and Management of Scleroderma Renal Crisis

Scleroderma renal crisis (SRC) is an uncommon complication of systemic sclerosis. Despite the advent of angiotensin-converting inhibitor therapy, SRC remains a life-threatening complication. Recent studies have contributed to a better understanding of SRC, but much remains unknown regarding its pathophysiology, risk factors, and optimal management. Genetic studies provide evidence that immune dysregulation might be a contributing factor, providing hope that further research in this direction might illuminate pathogenesis and provide novel predictors for this complication.

Aberrant immune response with consequent vascular and connective tissue remodeling - causal to scleroderma and associated syndromes such as Raynaud phenomenon and other fibrosing syndromes?

PURPOSE OF REVIEW

Scleroderma and other autoimmune-induced connective tissue diseases are characterized by dysfunctions in the immune system, connective tissue and the vasculature. We are focusing on systemic sclerosis (SSc)-associated pulmonary hypertension, which remains a leading cause of death with only a 50-60% of 2-year survival rate.

RECENT FINDINGS

Much research and translational efforts have been directed at understanding the immune response that causes SSc and the networked interactions with the connective tissue and the vasculature. One of the unexpected findings was that in some cases the pathogenic immune response in SSc resembles the immune response to helminth parasites. During coevolution, means of communication were developed which protect the host from over-colonization with parasites and which protect the parasite from excessive host responses. One explanation for the geographically clustered occurrence of SSc is that environmental exposures combined with genetic predisposition turn on triggers of molecular and cellular modules that were once initiated by parasites.

SUMMARY

Future research is needed to further understand the parasite-derived signals that dampen the host response. Therapeutic helminth infection or treatment with parasite-derived response modifiers could be promising new management tools for autoimmune connective tissue diseases.

Non-HLA antibodies against endothelial targets bridging allo- and autoimmunity

Detrimental actions of donor-specific antibodies (DSAs) directed against both major histocompatibility antigens (human leukocyte antigen [HLA]) and specific non-HLA antigens expressed on the allograft endothelium are a flourishing research area in kidney transplantation. Newly developed solid-phase assays enabling detection of functional non-HLA antibodies targeting G protein-coupled receptors such as angiotensin type I receptor and endothelin type A receptor were instrumental in providing long-awaited confirmation of their broad clinical relevance. Numerous recent clinical studies implicate angiotensin type I receptor and endothelin type A receptor antibodies as prognostic biomarkers for earlier occurrence and severity of acute and chronic immunologic complications in solid organ transplantation, stem cell transplantation, and systemic autoimmune vascular disease. Angiotensin type 1 receptor and endothelin type A receptor antibodies exert their pathophysiologic effects alone and in synergy with HLA-DSA. Recently identified antiperlecan antibodies are also implicated in accelerated allograft vascular pathology. In parallel, protein array technology platforms enabled recognition of new endothelial surface antigens implicated in endothelial cell activation. Upon target antigen recognition, non-HLA antibodies act as powerful inducers of phenotypic perturbations in endothelial cells via activation of distinct intracellular cell-signaling cascades. Comprehensive diagnostic assessment strategies focusing on both HLA-DSA and non-HLA antibody responses could substantially improve immunologic risk stratification before transplantation, help to better define subphenotypes of antibody-mediated rejection, and lead to timely initiation of targeted therapies. Better understanding of similarities and dissimilarities in HLA-DSA and distinct non-HLA antibody-related mechanisms of endothelial damage should facilitate discovery of common downstream signaling targets and pave the way for the development of endothelium-centered therapeutic strategies to accompany intensified immunosuppression and/or mechanical removal of antibodies.

Update in pulmonary arterial hypertension

Pulmonary arterial hypertension is a rare and progressive disease that mainly affects the pulmonary arterioles (precapillary), regardless of the triggering aetiology. The prevalence of pulmonary hypertension and pulmonary arterial hypertension in Spain is estimated at 19.2 and 16 cases per million inhabitants, respectively. The diagnosis of pulmonary arterial hypertension is based on haemodynamic criteria (mean pulmonary artery pressure ≥25mmHg, pulmonary capillary wedge pressure ≤15mmHg and pulmonary vascular resistance >3 Wood units) and therefore requires the implementation of right cardiac catheterisation. Sequential therapy with a single drug has been used in clinical practice. However, recent European guidelines recommend combined initial therapy in some situations. This review conducts a critical update of our knowledge of this disease according to the latest guidelines and recommendations.

C4d-negative antibody-mediated rejection with high anti-angiotensin II type I receptor antibodies in absence of donor-specific antibodies

AIMS

Acute antibody-mediated rejection can occur in absence of circulating donor-specific antibodies. Agonistic antibodies targeting the anti-angiotensin II type 1 receptor (anti-AT1 R) are emerging as important non-human leucocyte antigen (HLA) antibodies. Elevated levels of anti-angiotensin II receptor antibodies were first observed in kidney transplant recipients with malignant hypertension and allograft rejection. They have now been studied in three separate kidney transplant populations and associate to frequency of rejection, severity of rejection and graft failure.

METHODS

We report 11 cases of biopsy-proven, Complement 4 fragment d (C4d)-negative, acute rejection occurring without circulating donor-specific anti-HLA antibodies. In eight cases, anti-angiotensin receptor antibodies were retrospectively examined. The remaining three subjects were identified from our centre's newly instituted routine anti-angiotensin receptor antibody screening.

RESULTS

All subjects fulfilled Banff 2013 criteria for antibody-mediated rejection and all responded to anti-rejection therapy, which included plasma exchange and angiotensin receptor blocker therapy.

CONCLUSIONS

These cases support the routine assessment of anti-AT1 R antibodies in kidney transplant recipients to identify subjects at risk. Further studies will need to determine optimal assessment protocol and the effectiveness of pre-emptive treatment with angiotensin receptor blockers.

Role of B cells in the pathogenesis of systemic sclerosis

Systemic sclerosis (SSc) is an orphan disease characterized by progressive fibrosis of the skin and internal organs. Aside from vasculopathy and fibrotic processes, its pathogenesis involves an aberrant activation of immune cells, among which B cells seem to play a significant role. Indeed, B cell homeostasis is disturbed during SSc: the memory subset is activated and displays an increased susceptibility to apoptosis, which is responsible for their decreased number. This chronic loss of B cells enhances bone marrow production of the naïve subset that accounts for their increased number in peripheral blood. This permanent activation state can be explained mainly by two mechanisms: a dysregulation of B cell receptor (BCR) signaling, and an overproduction of B cell survival signals, B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL). These disturbances of B cell homeostasis induce several functional anomalies that participate in the inflammatory and fibrotic events observed during SSc: autoantibody production (some being directly pathogenic); secretion of pro-inflammatory and pro-fibrotic cytokines (interleukin-6); direct cooperation with other SSc-involved cells [fibroblasts, through transforming growth factor-β (TGF-β) signaling, and T cells]. These data justify the evaluation of anti-B cell strategies as therapeutic options for SSc, such as B cell depletion or blockage of B cell survival signaling.

PKCα Deficiency in Mice Is Associated with Pulmonary Vascular Hyperresponsiveness to Thromboxane A2 and Increased Thromboxane Receptor Expression

Pulmonary vascular hyperresponsiveness is a main characteristic of pulmonary arterial hypertension (PAH). In PAH patients, elevated levels of the vasoconstrictors thromboxane A2 (TXA2), endothelin (ET)-1 and serotonin further contribute to pulmonary hypertension. Protein kinase C (PKC) isozyme alpha (PKCα) is a known modulator of smooth muscle cell contraction. However, the effects of PKCα deficiency on pulmonary vasoconstriction have not yet been investigated. Thus, the role of PKCα in pulmonary vascular responsiveness to the TXA2 analog U46619, ET-1, serotonin and acute hypoxia was investigated in isolated lungs of PKCα-/- mice and corresponding wild-type mice, with or without prior administration of the PKC inhibitor bisindolylmaleimide I or Gö6976. mRNA was quantified from microdissected intrapulmonary arteries. We found that broad-spectrum PKC inhibition reduced pulmonary vascular responsiveness to ET-1 and acute hypoxia and, by trend, to U46619. Analogously, selective inhibition of conventional PKC isozymes or PKCα deficiency reduced ET-1-evoked pulmonary vasoconstriction. The pulmonary vasopressor response to serotonin was unaffected by either broad PKC inhibition or PKCα deficiency. Surprisingly, PKCα-/- mice showed pulmonary vascular hyperresponsiveness to U46619 and increased TXA2 receptor (TP receptor) expression in the intrapulmonary arteries. To conclude, PKCα regulates ET-1-induced pulmonary vasoconstriction. However, PKCα deficiency leads to pulmonary vascular hyperresponsiveness to TXA2, possibly via increased pulmonary arterial TP receptor expression.

Influence of Endothelin-1 in Aqueous Humor on Intermediate-Term Trabeculectomy Outcomes

Purpose. To investigate whether increased concentrations of ET-1 in aqueous humor of glaucoma patients influences surgical outcome of standard trabeculectomy with Mitomycin C. Methods. Retrospective chart review of 36 glaucoma patients with known ET-1 concentrations who had undergone trabeculectomy with Mitomycin C. Patients were divided into two groups based on their aqueous ET-1 concentration, a below-median (low ET-1) and an above-median (high ET-1) group. Postoperative IOP development, necessity of glaucoma medication, surgical success and complications, postoperative use of antifibrotics (5-FU), and number of additional glaucoma surgeries were compared between the groups. Results. Overall surgical success of trabeculectomy was comparable to published literature (90%, 81%, 76%, and 68% absolute success at 12, 24, 36, and 48 months after surgery). There was no difference between high and low ET-1 group in the postsurgical development of IOP, surgical success rate, or complication rate. There was no difference in postoperative scarring or indirect indicators thereof (e.g., number of 5-FU injections, needlings, suture lyses, or IOP lowering medications). Conclusion. In this set of patients, ET-1 in aqueous humor does not appear to have influenced surgical outcome of trabeculectomy with Mitomycin C. There is no indication of an increased likelihood of bleb fibrosis in patients with increased ET-1 concentrations.

Systemic sclerosis: An update in 2016

Systemic sclerosis (SSc) is a chronic immune disorder of unknown origin, dominated by excessive fibrosis responsible for cutaneous and pulmonary fibrosis, and by vascular endothelial dysfunction at the origin of skin ischemia, renal and pulmonary artery lesions. Renal and pulmonary complications are mainly responsible for the severity of the disease. Recent advances led to a better understanding of pathological mechanisms and a more accurate classification of patients according to clinical and biological (auto-antibodies) phenotype. Recent trials provided interesting data on different therapeutic strategies, depending on organ involvement. These data are of particular importance in such disease, still characterized by increased mortality and morbidity rates. In this review, we aim to synthetize recent advances in diagnosis and prognosis leading to better classification of SSc patients, and in therapeutic management.

Risk factors for severity and manifestations in systemic sclerosis and prediction of disease course

Systemic sclerosis (SSc, or scleroderma) is a rheumatic disease with distinct features that encompass autoimmunity, vascular lesions (vasculopathy) and tissue fibrosis. The disease has a high morbidity and mortality compared with other rheumatic diseases. This review discusses risk factors and markers that predict the disease course and the occurrence of disease manifestations, with an emphasis on major organ involvement. In addition, risk factors will be described that are associated with mortality in SSc patients. The review addresses the impact of recent developments on screening, diagnosis and risk stratification as well as the need for further research where data are lacking.

Anti-Endothelin Receptor Type A Autoantibodies in Systemic Lupus Erythematosus-Associated Pulmonary Arterial Hypertension

OBJECTIVE

To investigate the role of autoantibodies against endothelin 1 receptor type A (ETRA) in patients with systemic lupus erythematosus (SLE)-associated pulmonary arterial hypertension (PAH) and to examine the possibility that the pathogenesis of this disease is mediated by these autoantibodies.

METHODS

ETRA autoantibodies in serum from patients with SLE-associated PAH and serum from controls (SLE patients without PAH) were detected via a human ETRA epitope peptide-based enzyme-linked immunosorbent assay. An exploratory cohort of patients with SLE-associated PAH (n = 76) and an independent validation cohort of patients with SLE-associated PAH confirmed by right-sided heart catheterization (RHC) (n = 82) were enrolled. The clinical relevance of ETRA autoantibodies in SLE-associated PAH was analyzed. The proliferation of vascular smooth muscle cells (SMCs) and the permeability of endothelial cells (ECs) were assessed in vitro in cells stimulated with polyclonal ETRA IgG autoantibodies. Expression of PAH-related markers, i.e., serotonin transporter, platelet-derived growth factor receptor β, vascular endothelial growth factor A, and platelet-derived growth factor B was measured by quantitative polymerase chain reaction. In addition, a suboptimal dose of monocrotaline was used to induce PAH in rats, and the effect of ETRA autoantibodies in vivo was determined using a right ventricular hypertrophy index, pulmonary angiography, and laboratory parameters.

RESULTS

ETRA autoantibodies occurred more frequently in SLE-associated PAH (41.5%) than in controls (17.1%). There was a significant correlation between ETRA autoantibody titers and pulmonary artery systolic pressure measured by echocardiography (r = 0.2978, P = 0.0038) or pulmonary artery systolic pressure measured by RHC (r = 0.2159, P = 0.0257) in SLE-associated PAH. ETRA autoantibodies could promote SMC proliferation, disrupt the endothelial barrier, and up-regulate expression of PAH-related markers, which could be blocked in the presence of an endothelin receptor antagonist. ETRA autoantibodies aggravated right ventricular hypertrophy and vascular remodeling in vivo.

CONCLUSION

We identified ETRA autoantibodies as a biomarker of mechanistic relevance in SLE. These autoantibodies may mediate PAH development in SLE.

Systemic sclerosis: New evidence re-enforces the role of B cells

Systemic sclerosis (SSc) is characterized by widespread fibrosis, microangiopathy (vasospasms and stenosis), and formation of autoantibodies. T cell activation has been shown to contribute to fibrosis and microvasculopathy in SSc. However, recent evidence suggests that B cells are also likely to contribute in the pathogenesis of the disease. B cells are hyperactivated in SSc, as indicated by the overexpression of the stimulatory CD19 receptor and impairment of the inhibitory CD22 receptor. They lead to the production of many autoantibodies, some of which induce collagen production and vasoconstriction. They promote fibroblast collagen production through cell contact. Furthermore, B cells can function as antigen-presenting cells to T cells and induce dendritic cell maturation that promotes profibrotic Th2 response. Lately, interleukin (IL)-10-producing B regulatory cells, which induce generation of T regulatory cells and can ameliorate autoimmune diseases, were found to be reduced in SSc, favoring autoaggression of B cells in this disease. Finally, B cell depletion with rituximab improves or stabilizes skin fibrosis and lung function. These finding suggest that new therapeutic strategies targeting B cell function(s) can be developed for SSc.

Associations between circulating endostatin levels and vascular organ damage in systemic sclerosis and mixed connective tissue disease: an observational study

Introduction

Systemic sclerosis (SSc) and mixed connective tissue disease (MCTD) are chronic immune-mediated disorders complicated by vascular organ damage. The aim of this study was to examine the serum levels of the markers of neoangiogenesis: endostatin and vascular endothelial growth factor (VEGF), in our unselected cohorts of SSc and MCTD.

Methods

Sera of SSc patients (N = 298) and MCTD patients (N = 162) from two longitudinal Norwegian cohorts were included. Blood donors were included as controls (N = 100). Circulating VEGF and endostatin were analyzed by enzyme immunoassay.

Results

Mean endostatin levels were increased in SSc patients 93.7 (37) ng/ml (P < .001) and MCTD patients 83.2 (25) ng/ml (P < .001) compared to controls 65.1 (12) ng/ml. Median VEGF levels were elevated in SSc patients 209.0 (202) pg/ml compared to MCTD patients 181.3 (175) pg/ml (P = .017) and controls 150.0 (145) pg/ml (P < .001). Multivariable analysis of SSc subsets showed that pulmonary arterial hypertension (coefficient 15.7, 95 % CI: 2.2–29.2, P = .023) and scleroderma renal crisis (coefficient 77.6, 95 % CI: 59.3–100.0, P < .001) were associated with elevated endostatin levels. Multivariable analyses of MCTD subsets showed that digital ulcers were associated with elevated endostatin levels (coefficient 10.5, 95 % CI: 3.2–17.8, P = .005). The risk of death increased by 1.6 per SD endostatin increase (95 % CI: 1.2–2.1, P = .001) in the SSc cohort and by 1.6 per SD endostatin increase (95 % CI: 1.0–2.4, P = .041) in the MCTD cohort after adjustments to known risk factors.

Conclusions

Endostatin levels were elevated in patients with SSc and MCTD, particularly SSc patients with pulmonary arterial hypertension and scleroderma renal crisis, and MCTD patients with digital ulcers. Elevated endostatin levels were also associated with increased all-cause mortality during follow-up in both groups of patients. We propose that endostatin might indicate the degree of vascular injury in SSc and MCTD patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0756-5) contains supplementary material, which is available to authorized users.

Autoantibodies against Endothelin 1 Type A Receptor Are Strong Predictors of Digital Ulcers in Systemic Sclerosis

OBJECTIVE

To determine the predictive value of functional autoantibodies against vascular receptors for the development of ischemic digital ulcers (DU) in patients with systemic sclerosis (SSc).

METHODS

Angiotensin II Type 1 receptor (AT1R) and endothelin 1 Type A receptor (ETAR) autoantibodies were measured at baseline in a prospective cohort of 90 patients with SSc together with 5 validated angiogenic markers. The primary outcome was the occurrence of at least 1 new ischemic DU during the 5-year followup.

RESULTS

Twenty-four patients developed at least 1 new DU during the followup period. Univariate Cox analysis revealed that concentrations above the median value of anti-AT1R and anti-ETAR antibodies were predictive of the occurrence of ischemic DU (HR 2.85, 95% CI 1.19-6.84 and HR 3.39, 95% CI 1.35-8.50, respectively). A first multivariate Cox analysis including functional autoantibodies and clinical predictors of new DU confirmed anti-ETAR autoantibodies as independent predictors of the occurrence of new ischemic DU (HR 3.15, 95% CI 1.22-8.13) together with a history of DU at baseline. In a second model implemented with angiogenic markers, anti-ETAR autoantibodies remained an independent predictor of the occurrence of new ischemic DU (HR 9.59, 95% CI 1.75-52.64) together with the presence at baseline of active DU or history of DU.

CONCLUSION

Anti-ETAR autoantibodies can be used together with the presence of current or past DU to identify patients with SSc who are at risk for the development of subsequent DU. These autoantibodies may allow for earlier management and therapeutic intervention.

Update on biomarkers in systemic sclerosis: tools for diagnosis and treatment

Systemic sclerosis (SSc) is a complex autoimmune disease in which immune activation, vasculopathy, and extensive fibrosis of the skin and internal organs are among the principal features. SSc is a heterogeneous disease with varying manifestations and clinical outcomes. Currently, patients’ clinical evaluation often relies on subjective measures, non-quantitative methods, or requires invasive procedures as markers able to predict disease trajectory or response to therapy are lacking. Therefore, current research is focusing on the discovery of useful biomarkers reflecting ongoing inflammatory or fibrotic activity in the skin and internal organs, as well as being predictive of future disease course. Recently, remarkable progress has been made towards a better understanding of numerous mechanisms involved in the pathogenesis of SSc. This has opened new possibilities for the development of novel biomarkers and therapy. However, current proposed biomarkers that could reliably describe various aspects of SSc still require further investigation. This review will summarize studies describing the commonly used and validated biomarkers, the newly emerging and promising SSc biomarkers identified to date, and consideration of future directions in this field.

The Effects of Antigen-Specific IgG1 Antibody for the Pulmonary-Hypertension-Phenotype and B Cells for Inflammation in Mice Exposed to Antigen and Fine Particles from Air Pollution

Air pollution is known to exacerbate chronic inflammatory conditions of the lungs including pulmonary hypertension, cardiovascular diseases and autoimmune diseases. Directly pathogenic antibodies bind pro-inflammatory cell receptors and cause or exacerbate inflammation. In contrast, anti-inflammatory antibody isotypes (e.g. mouse immunoglobulin G1, IgG1) bind inhibitory cell receptors and can inhibit inflammation. Our previous studies showed that co-exposure to antigen and urban ambient particulate matter (PM_2.5) induced severe pulmonary arterial thickening and increased right ventricular systolic pressures in mice via T-cell produced cytokines, Interleukin (IL)-13 and IL-17A. The aim of the current study was to understand how B cell and antibody responses integrate into this T cell cytokine network for the pulmonary hypertension phenotype. Special focus was on antigen-specific IgG1 that is the predominant antibody in the experimental response to antigen and urban ambient PM_2.5. Wild type and B cell-deficient mice were primed with antigen and then challenged with antigen and urban particulate matter and injected with antibodies as appropriate. Our data surprisingly showed that B cells were necessary for the development of increased right ventricular pressures and molecular changes in the right heart in response to sensitization and intranasal challenge with antigen and PM_2.5. Further, our studies showed that both, the increase in right ventricular systolic pressure and right ventricular molecular changes were restored by reconstituting the B cell KO mice with antigen specific IgG1. In addition, our studies identified a critical, non-redundant role of B cells for the IL-17A-directed inflammation in response to exposure with antigen and PM_2.5, which was not corrected with antigen-specific IgG1. In contrast, IL-13-directed inflammatory markers, as well as severe pulmonary arterial remodeling induced by challenge with antigen and PM_2.5 were similar in B cell-deficient and wild type mice. Our studies have identified B cells and antigen specific IgG1 as potential therapeutic targets for pulmonary hypertension associated with immune dysfunction and environmental exposures.

Macro- and microvascular disease in systemic sclerosis

Vasculopathy is common in patients with connective tissue disease and can be directly implicated in the pathogenesis of the disease. Systemic sclerosis is an auto-immune multiorgan connective tissue disorder characterized by fibrosis of the skin and visceral organs and vascular disease. Micro- and macro-vessels are a direct target of the disease. In this review, we present the various clinical manifestations of the vasculopathy that can be present in SSc patients, and then discuss the various aspects of the pathophysiology of the vascular disorders.

Monitoring and Diagnostic Approaches for Pulmonary Arterial Hypertension in Patients with Systemic Sclerosis

Pulmonary arterial hypertension (PAH) is one of the leading causes of death in patients with systemic sclerosis (SSc). Given the high prevalence and poor survival of SSc-PAH, and that aggressive management of mild disease may be associated with better outcomes, screening is critical. Right heart catheterization (RHC) is the gold standard for the definitive diagnosis of PAH, and should be performed in those patients in whom this diagnosis is suspected. Once a diagnosis of PAH is confirmed by RHC, treatment with PAH-specific therapies should be initiated as soon as possible.

Activation of renin-angiotensin-aldosterone system (RAAS) in the lung of smoking-induced pulmonary arterial hypertension (PAH) rats

Objectives:

To explore the role of the renin–angiotensin–aldosterone system (RAAS) in the pathogenesis of pulmonary arterial hypertension (PAH) induced by chronic exposure to cigarette smoke.

Methods:

48 healthy male SD rats were randomly divided into four groups (12/group): control group (group A); inhibitor alone group (group B); cigarette induction group (group C); cigarette induction + inhibitor group (group D). After the establishment of smoking-induced PAH rat model, the right ventricular systolic pressure (RVSP) was detected using an inserted catheter; western blotting was used to detect the protein expression of angiotensin-converting enzyme-2 (ACE2) and angiotensin-converting enzyme (ACE); expression levels of angiotensin II (AngII) in lung tissue were measured by radioimmunoassay.

Results:

After six months of cigarette exposure, the RVSP of chronic cigarette induction group was significantly higher than that of the control group; expression levels of AngII and ACE increased in lung tissues, but ACE2 expression levels reduced. Compared with cigarette exposure group, after losartan treatment, RVSP, ACE and AngII obviously decreased (P<0.05), and ACE2 expression levels significantly increased.

Conclusion:

Chronic cigarette exposure may result in PAH and affect the protein expression of ACE2 and ACE in lung tissue, suggesting that ACE2 and ACE play an important role in the pathogenesis of smoking-induced PAH.

Connective tissue disease-associated pulmonary arterial hypertension

Although rare in its idiopathic form, pulmonary arterial hypertension (PAH) is not uncommon in association with various associated medical conditions, most notably connective tissue disease (CTD). In particular, it develops in approximately 10% of patients with systemic sclerosis and so these patients are increasingly screened to enable early detection. The response of patients with systemic sclerosis to PAH-specific therapy appears to be worse than in other forms of PAH. Survival in systemic sclerosis-associated PAH is inferior to that observed in idiopathic PAH. Potential reasons for this include differences in age, the nature of the underlying pulmonary vasculopathy and the ability of the right ventricle to cope with increased afterload between patients with systemic sclerosis-associated PAH and idiopathic PAH, while coexisting cardiac and pulmonary disease is common in systemic sclerosis-associated PAH. Other forms of connective tissue-associated PAH have been less well studied, however PAH associated with systemic lupus erythematosus (SLE) has a better prognosis than systemic sclerosis-associated PAH and likely responds to immunosuppression.