Idiopathic and connective tissue disease-associated pulmonary arterial hypertension (PAH): Similarities, differences and the role of autoimmunity.

Pre-capillary pulmonary arterial hypertension (PAH) is hemodynamically characterized by a mean pulmonary arterial pressure (mPAP) ≥ 20 mmHg, pulmonary capillary wedge pressure (PAWP) ≤15 mmHg and pulmonary vascular resistance (PVR) > 2. PAH is classified in six clinical subgroups, including idiopathic PAH (IPAH) and PAH associated to connective tissue diseases (CTD-PAH), that will be the main object of this review. The aim is to compare these two PAH subgroups in terms of epidemiology, histological and pathogenic findings in an attempt to define disease-specific features, including autoimmunity, that may explain the heterogeneity of response to therapy between IPAH and CTD-PAH.

Endothelin B Receptor Immunodynamics in Pulmonary Arterial Hypertension.

Introduction: Inflammation is a major pathological feature of pulmonary arterial hypertension (PAH), particularly in the context of inflammatory conditions such as systemic sclerosis (SSc). The endothelin system and anti-endothelin A receptor (ETA) autoantibodies have been implicated in the pathogenesis of PAH, and endothelin receptor antagonists are routinely used treatments for PAH. However, immunological functions of the endothelin B receptor (ETB) remain obscure. Methods: Serum levels of anti-ETB receptor autoantibodies were quantified in healthy donors and SSc patients with or without PAH. Age-dependent effects of overexpression of prepro-endothelin-1 or ETB deficiency on pulmonary inflammation and the cardiovascular system were studied in mice. Rescued ETB-deficient mice (ETB-/-) were used to prevent congenital Hirschsprung disease. The effects of pulmonary T-helper type 2 (Th2) inflammation on PAH-associated pathologies were analyzed in ETB-/- mice. Pulmonary vascular hemodynamics were investigated in isolated perfused mouse lungs. Hearts were assessed for right ventricular hypertrophy. Pulmonary inflammation and collagen deposition were assessed via lung microscopy and bronchoalveolar lavage fluid analyses. Results: Anti-ETB autoantibody levels were elevated in patients with PAH secondary to SSc. Both overexpression of prepro-endothelin-1 and rescued ETB deficiency led to pulmonary hypertension, pulmonary vascular hyperresponsiveness, and right ventricular hypertrophy with accompanying lymphocytic alveolitis. Marked perivascular lymphocytic infiltrates were exclusively found in ETB-/- mice. Following induction of pulmonary Th2 inflammation, PAH-associated pathologies and perivascular collagen deposition were aggravated in ETB-/- mice. Conclusion: This study provides evidence for an anti-inflammatory role of ETB. ETB seems to have protective effects on Th2-evoked pathologies of the cardiovascular system. Anti-ETB autoantibodies may modulate ETB-mediated immune homeostasis.

Central Role of Dendritic Cells in Pulmonary Arterial Hypertension in Human and Mice.

The pathogenesis of idiopathic pulmonary arterial hypertension (IPAH) is not fully understood, but evidence is accumulating that immune dysfunction plays a significant role. We previously reported that 31-week-old Tnfaip3DNGR1-KO mice develop pulmonary hypertension (PH) symptoms. These mice harbor a targeted deletion of the TNFα-induced protein-3 (Tnfaip3) gene, encoding the NF-κB regulatory protein A20, specifically in type I conventional dendritic cells (cDC1s). Here, we studied the involvement of dendritic cells (DCs) in PH in more detail. We found various immune cells, including DCs, in the hearts of Tnfaip3DNGR1-KO mice, particularly in the right ventricle (RV). Secondly, in young Tnfaip3DNGR1-KO mice, innate immune activation through airway exposure to toll-like receptor ligands essentially did not result in elevated RV pressures, although we did observe significant RV hypertrophy. Thirdly, PH symptoms in Tnfaip3DNGR1-KO mice were not enhanced by concomitant mutation of bone morphogenetic protein receptor type 2 (Bmpr2), which is the most affected gene in PAH patients. Finally, in human IPAH lung tissue we found co-localization of DCs and CD8+ T cells, representing the main cell type activated by cDC1s. Taken together, these findings support a unique role of cDC1s in PAH pathogenesis, independent of general immune activation or a mutation in the Bmpr2 gene.

Identification of Potential Risk Genes and the Immune Landscape of Idiopathic Pulmonary Arterial Hypertension via Microarray Gene Expression Dataset Reanalysis.

Gene dysfunction and immune cell infiltration play an essential role in the pathogenesis of idiopathic pulmonary arterial hypertension (IPAH). We aimed to investigate the immune landscape and novel differentially expressed genes (DEGs) of IPAH. In addition, potential druggable molecular targets for IPAH were also explored. In this study, the GSE117261 dataset was reanalyzed to explore the immune landscape and hub DEGs of IPAH. Lasso Cox regression analysis and receiver operating characteristic curve analysis were performed to detect the predictive value of IPAH. Additionally, the underlying drug targets for IPAH treatment were determined by drug-gene analysis. IPAH was significantly associated with the transforming growth factor-ß (TGF-ß) signaling pathway and Wnt signaling pathway as well as energetic metabolism dysfunction. We identified 31 upregulated and 39 downregulated DEGs in IPAH patients. Six hub genes, namely, SAA1, CCL5, CXCR1, CXCR2, CCR1, and ADORA3, were related to IPAH pathogenesis regardless of sex differences. Prediction model analysis showed that the area under the curve values of the hub DEGs except CXCR2 were all above 0.9 for distinguishing IPAH patients. In addition, the relative proportions of 5 subtypes of immune cells, namely, CD8+ T cells, CD4+ memory resting T cells, γ delta T cells, M1 macrophages, and resting mast cells, were significantly upregulated in the IPAH samples, while 6 subtypes of immune cells, namely, CD4+ naive T cells, resting NK cells, monocytes, M0 macrophages, activated mast cells, and neutrophils, were downregulated. Additionally, a total of 17 intersecting drugs targeting 5 genes, CCL5, CXCR1, CXCR2, CCR1, and ADORA3, were generated as potential druggable molecular targets for IPAH. Our study revealed the underlying correlations between genes and immune cells in IPAH and demonstrated for the first time that SAA1, CCL5, CXCR1, CCR1, and ADORA3 may be novel genetic targets for IPAH.

Prevalence of auto-antibodies associated to pulmonary arterial hypertension in scleroderma - A review.

The prevalence of auto-antibodies associated to pulmonary arterial hypertension in scleroderma patients was reviewed, based on reports cited in two major scientific databases. Data were collected on the following types of antibodies: antinuclear, anti-double-stranded DNA, anticentromere, anti-CENP-A, anti-CENP-B, anti-bicaudal D2, anti-nucleolar, anti-Scl-70 (anti-topoisomerase I), anti-topoisomerase II α, anti-RNP, anti-U1RNP, anti-U3RNP, anti-RNA polymerase III, anti-Th/To, anti-histone, antiphospholipid, anti-PmScl, anti-Sm, anti SSA (anti-Ro),anti SSB (La), anti-Ro52 (TRIM 21), anti-Ku, anti-B23, anti-RuvBL1, anti-RuvBL2, anti-fibrin bound tissue plasminogen activator, anti-endothelial cell, anti-phosphatidylserine-prothrombin complex, anti-endothelin-1 type A receptor, anti-angiotensin II type 1 receptor, anti­carbonic anhydrase II, anti-fibroblast, anti-cyclic citrullinated peptide, anti-4-sulfated N-Acetyl-lactosamine, class I and II anti-human leukocyte antigen. Auto-antibodies were shown by different authors to be associated to this condition, with different prevalence values for each type of auto-antibody. Antinuclear antibodies, anti-centromere antibodies, antiphospholipid antibodies, anti-U3 RNP antibodies and anti-Th/To antibodies would appear to show a particularly important prevalence in scleroderma patients with pulmonary hypertension, appearing in about 8/10 (antinuclear), 1/ 2 (anti-centromere, anti-phospholipid), and 1/4 (anti-U3RNP, anti-Th/To) of patients. The available evidence points in the direction of a strong association between auto-immune mechanisms and pulmonary hypertension in the setting of scleroderma.

Circulating plasmablasts are elevated and produce pathogenic anti-endothelial cell autoantibodies in idiopathic pulmonary arterial hypertension.

Idiopathic pulmonary arterial hypertension (IPAH) is a devastating pulmonary vascular disease in which autoimmune and inflammatory phenomena are implicated. B cells and autoantibodies have been associated with IPAH and identified as potential therapeutic targets. However, the specific populations of B cells involved and their roles in disease pathogenesis are not clearly defined. We aimed to assess the levels of activated B cells (plasmablasts) in IPAH, and to characterize recombinant antibodies derived from these plasmablasts. Blood plasmablasts are elevated in IPAH, remain elevated over time, and produce IgA autoantibodies. Single-cell sequencing of plasmablasts in IPAH revealed repertoires of affinity-matured antibodies with small clonal expansions, consistent with an ongoing autoimmune response. Recombinant antibodies representative of these clonal lineages bound known autoantigen targets and displayed an unexpectedly high degree of polyreactivity. Representative IPAH plasmablast recombinant antibodies stimulated human umbilical vein endothelial cells to produce cytokines and overexpress the adhesion molecule ICAM-1. Together, our results demonstrate an ongoing adaptive autoimmune response involving IgA plasmablasts that produce anti-endothelial cell autoantibodies in IPAH. These antibodies stimulate endothelial cell production of cytokines and adhesion molecules, which may contribute to disease pathogenesis. These findings suggest a role for mucosally-driven autoimmunity and autoimmune injury in the pathogenesis of IPAH.

Acute effects of exercise on the inflammatory state in patients with idiopathic pulmonary arterial hypertension.

BACKGROUND: Exercise training positively influences exercise tolerance and functional capacity of patients with idiopathic pulmonary arterial hypertension (IPAH). However, the underlying mechanisms are unclear. We hypothesized that exercise modulates the activated inflammatory state found in IPAH patients. METHODS: Single cardiopulmonary exercise testing was performed in 16 IPAH patients and 10 healthy subjects. Phenotypic characterization of peripheral blood mononuclear cells and circulating cytokines were assessed before, directly after and 1 h after exercise. RESULTS: Before exercise testing, IPAH patients showed elevated Th2 lymphocytes, regulatory T lymphocytes, IL-6, and TNF-alpha, whilst Th1/Th17 lymphocytes and IL-4 were reduced. In IPAH patients but not in healthy subject, exercise caused an immediate relative decrease of Th17 lymphocytes and a sustained reduction of IL-1-beta and IL-6. The higher the decrease of IL-6 the higher was the peak oxygen consumption of IPAH patients. CONCLUSIONS: Exercise seems to be safe from an immune and inflammatory point of view in IPAH patients. Our results demonstrate that exercise does not aggravate the inflammatory state and seems to elicit an immune-modulating effect in IPAH patients.

Regulatory T Cell Dysfunction in Idiopathic, Heritable and Connective Tissue-Associated Pulmonary Arterial Hypertension.

BACKGROUND: Pulmonary arterial hypertension (PAH) encompasses a group of conditions with distinct causes. Immunologic disorders are common features of all forms of PAH and contributes to both disease susceptibility and progression. Regulatory T lymphocytes (Treg) are dysfunctional in patients with idiopathic PAH (iPAH) in a leptin-dependent manner. However, it is not known whether these abnormalities are specific to iPAH. Hence, we hypothesized that (1) Treg dysfunction is also present in heritable (hPAH) and connective tissue disease-associated PAH (CTD-PAH); (2) defective leptin-dependent signaling is present in hPAH and CTD-PAH and could contribute to Treg dysfunction; (3) modulating the leptin axis in vivo could protect against Treg dysfunction; and (4) restoration of Treg activity could limit or reverse experimental chronic hypoxia-induced pulmonary hypertension in vivo. METHODS: We analyzed 62 patients with PAH (30 with iPAH, 18 with hPAH, and 14 with CTD-PAH), 7 patients with CTD without PAH, and 20 healthy control subjects. RESULTS: Our results indicate that Treg are dysfunctional in all PAH forms tested, as well as in patients with CTD without PAH. Importantly, the leptin axis is crucial in Treg dysfunction in patients with iPAH and those with CTD (with or without PAH), whereas in patients with hPAH, Treg are altered in a leptin-independent manner. We found that leptin receptor-deficient rats, which develop less severe hypoxia-induced pulmonary hypertension, are protected against decreased Treg function after hypoxic exposure. CONCLUSIONS: Taken together, our results suggest that Treg dysfunction is common to all forms of PAH and may contribute to the development and the progression of the disease.

Proinflammatory Signature of the Dysfunctional Endothelium in Pulmonary Hypertension. Role of the Macrophage Migration Inhibitory Factor/CD74 Complex.

RATIONALE: Inflammation and endothelial dysfunction are considered two primary instigators of pulmonary arterial hypertension (PAH). CD74 is a receptor for the proinflammatory cytokine macrophage migration inhibitory factor (MIF). This ligand/receptor complex initiates survival pathways and cell proliferation, and it triggers the synthesis and secretion of major proinflammatory factors and cell adhesion molecules. OBJECTIVES: We hypothesized that the MIF/CD74 signaling pathway is overexpressed in idiopathic PAH (iPAH) and contributes to a proinflammatory endothelial cell (EC) phenotype. METHODS: Primary early passage cultures of human ECs isolated from lung tissues obtained from patients with iPAH and controls were examined for their ability to secrete proinflammatory mediators and bind inflammatory cells with or without modulation of the functional activities of the MIF/CD74 complex. In addition, we tested the efficacies of curative treatments with either the MIF antagonist ISO-1 or anti-CD74 neutralizing antibodies on the aberrant proinflammatory EC phenotype in vitro and in vivo and on the progression of monocrotaline-induced pulmonary hypertension. MEASUREMENTS AND MAIN RESULTS: In human lung tissues, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin expressions are markedly up-regulated in the endothelium of distal iPAH pulmonary arteries. Circulating MIF levels are increased in the serum of patients with PAH compared with control subjects, and T-cell lymphocytes represent a source of this overabundance. In addition, CD74 is highly expressed in the endothelium of muscularized pulmonary arterioles and in cultured pulmonary ECs from iPAH, contributing to an exaggerated recruitment of peripheral blood mononuclear cells to pulmonary iPAH ECs. Finally, we found that curative treatments with the MIF antagonist ISO-1 or anti-CD74 neutralizing antibodies partially reversed development of pulmonary hypertension in rats and substantially reduced inflammatory cell infiltration. CONCLUSIONS: We report here that CD74 and MIF are markedly increased and activated in patients with iPAH, contributing to the abnormal proinflammatory phenotype of pulmonary ECs in iPAH.

Sequence-based prediction of linear autoepitopes involved in pathogenesis of IPAH and the corresponding organism sources of molecular mimicry.

We proposed here a sequence-based approach predicting some microorganisms as possible sources of autoantigen-related molecular mimicry concerning Idiopathic Pulmonary Arterial Hypertension (IPAH) and related hypertension mostly accompanying autoimmune diseases and AIDS (APAH). This approach (SPECIES_VALENCE) processes the database occurrences of linear autoepitope-related short Dense Quasi-Pattern Sequences (DQPA) generated based on identities of important autoantigenic sequences. The corresponding enumeration comprises two types of statistical evaluations performed in each of eight proposed models. Based on this enumeration, we selected nine microorganisms, whereas revaluation of the obtained scoring values restricted Pseudomonas aeruginosa, Aspergillus fumigatus and the two co-infecting herpes viruses (Epstein Barr virus and cytomegalovirus) as most favourable. The results are discussed in terms of (a) the validity of increased DQPA occurrence in functionally correlated sequences, (b) the possible mechanisms leading to autoantibody response, (c) selected additional pathogenic effects of predicted microorganisms and (d) possible effects of cross-reactivities and immune tolerance.