Prevalence of Anti-endothelial Cell Antibodies in Patients with Pulmonary Arterial Hypertension Associated with Connective Tissue Diseases

B-cells in pulmonary arterial hypertension: friend, foe or bystander?

There is an unmet need for new therapeutic strategies that target alternative pathways to improve the prognosis of patients with pulmonary arterial hypertension (PAH). As immunity has been involved in the development and progression of vascular lesions in PAH, we review the potential contribution of B-cells in its pathogenesis and evaluate the relevance of B-cell-targeted therapies. Circulating B-cell homeostasis is altered in PAH patients, with total B-cell lymphopenia, abnormal subset distribution (expansion of naïve and antibody-secreting cells, reduction of memory B-cells) and chronic activation. B-cells are recruited to the lungs through local chemokine secretion, and activated by several mechanisms: 1) interaction with lung vascular autoantigens through cognate B-cell receptors; 2) costimulatory signals provided by T follicular helper cells (interleukin (IL)-21), type 2 T helper cells and mast cells (IL-4, IL-6 and IL-13); and 3) increased survival signals provided by B-cell activating factor pathways. This activity results in the formation of germinal centres within perivascular tertiary lymphoid organs and in the local production of pathogenic autoantibodies that target the pulmonary vasculature and vascular stabilisation factors (including angiotensin-II/endothelin-1 receptors and bone morphogenetic protein receptors). B-cells also mediate their effects through enhanced production of pro-inflammatory cytokines, reduced anti-inflammatory properties by regulatory B-cells, immunoglobulin (Ig)G-induced complement activation, and IgE-induced mast cell activation. Precision-medicine approaches targeting B-cell immunity are a promising direction for select PAH conditions, as suggested by the efficacy of anti-CD20 therapy in experimental models and a trial of rituximab in systemic sclerosis-associated PAH.

Raynaud's phenomenon-an update on diagnosis, classification and management

Raynaud's phenomenon (RP) is used to describe a symptom complex caused by digital vascular compromise. RP is a clinical diagnosis. The typically episodic nature of RP has resulted in a reliance upon patient self-report for diagnosis. The term 'primary RP' is generally applied when no underlying pathology can be demonstrated. Whilst 'primary RP' is currently considered a distinct disorder, there is evidence that the term may comprise several entities that include a functional vasospastic disorder, a physiologically appropriate thermoregulatory response, subclinical atherosclerosis and 'cold intolerance'. Optimal management may differ depending on cause. The term 'secondary RP' encompasses a broad range of rheumatological, haematological, endocrinological and vascular pathology. RP can range from relatively benign but intrusive vasospasm, to the progressive obliterative microangiopathy of systemic sclerosis (SSc), in which severe digital ischaemia can threaten tissue viability. SSc has formed the focus of much of the research into RP but, consistent with most medical symptom complexes, the aetiopathogenesis of RP varies greatly dependent on cause. Vasospasm within the digital macro- and microvasculature occurs in SSc, but digital ischaemia is further compounded by a progressive obliterative microangiopathy. Recent work exploring the patient experience of SSc-RP is challenging the 'episodic' paradigm of 'Raynaud's', with important implications for clinical trials utilising diary-based patient-reported outcome instruments for assessing Raynaud's symptoms. This review shall examine the causes, pathogenesis, clinical features, classification and management of RP. A practical approach to the evaluation and management of RP is outlined, highlighting important knowledge gaps and unmet research needs where applicable. Key Points • Raynaud's phenomenon is a symptom complex related to digital vascular compromise secondary to broad-ranging pathology. • Raynaud's phenomenon, as currently classified, likely encompasses a number of aetiopathogenic processes. • Raynaud's phenomenon causes significant disease-related morbidity in autoimmune rheumatic diseases such as systemic sclerosis.

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.

Pulmonary arterial hypertension in SLE: what do we know?

Pulmonary hypertension (PH) can occur at any time during the course of systemic lupus erythematosus (SLE), and can be independent of lupus disease activity in other systems. The pathogenesis of PH in SLE can be multifactorial, but pulmonary arterial hypertension (PAH) is the commonest cause of PH in SLE. The international PH registries have published that approximately 15% of connective tissue disease-associated PH is lupus related in their cohorts. As the symptoms of PH in SLE can be mild and non-specific in early stages, an increasing awareness of this devastating complication is essential for early diagnosis. Echocardiographic evaluation of several right heart variables in addition to systolic pulmonary artery pressure estimation reduces false positive rates for PH detection. Antiphospholipid antibodies may predict SLE-PAH. Prompt treatment of PAH with newer PAH therapy as well as immunosuppression can reduce morbidity and prolong survival. The survival in SLE-associated PAH is better compared with systemic sclerosis-associated PH but worse than idiopathic PAH. Pregnancy in SLE-PAH can result in a fatal outcome, especially in severe and poorly controlled PH at onset.

The role of inflammation and autoimmunity in the pathophysiology of pulmonary arterial hypertension

Pulmonary arterial hypertension is characterized by a remodeling of pulmonary arteries with endothelial cell, fibroblast, and vascular smooth muscle cell activation and proliferation. Since pulmonary arterial hypertension occurs frequently in autoimmune conditions such as systemic sclerosis, inflammation and autoimmunity have been suspected to play a critical role in both idiopathic pulmonary arterial hypertension and systemic sclerosis-associated pulmonary arterial hypertension. High levels of pro-inflammatory cytokines such as interleukin-1 and interleukin-6, platelet-derived growth factor, or macrophage inflammatory protein 1 have been found in lung samples of patients with pulmonary arterial hypertension, along with inflammatory cell infiltrates mainly composed of macrophages and dendritic cells, T and B lymphocytes. In addition, circulating autoantibodies are found in the peripheral blood of patients. Thus, autoimmunity and inflammation probably play a role in the development of pulmonary arterial hypertension. In this setting, it would be important to set-up new experimental models of pulmonary arterial hypertension, in order to define novel therapeutics that specifically target immune disturbances in this devastating condition.

[Novel immunopathological approaches to pulmonary arterial hypertension]

Inflammation is important for the initiation and the maintenance of vascular remodeling in the most commun animal models of pulmonary hypertension (PH), and its therapeutical targeting blocks PH development in these models. In human, pulmonary vascular lesions of PH are also the source of an intense chemokine production, linked to inflammatory cell recruitment. However, arteritis is uncommon in PH patients. Of note, current PH treatments have immunomodulatory properties. In addition, some studies have shown a correlation between levels of circulating inflammatory mediators and patients' survival. The study of autoimmunity in the pathophysiology of pulmonary arterial hypertension is becoming an area of intense investigation. New immunopathological approaches to PH should allow the development of innovative treatments for this very severe condition.