BACKGROUND Immune dysregulation has been linked to occlusive vascular remodeling in pulmonary arterial hypertension (PAH) that is hereditary, idiopathic, or associated with other conditions. Circulating autoantibodies, lung perivascular lymphoid tissue, and elevated cytokines have been related to PAH pathogenesis but without a clear understanding of how these abnormalities are initiated, perpetuated, and connected in the progression of disease. We therefore set out to identify specific target antigens in PAH lung immune complexes as a starting point toward resolving these issues to better inform future application of immunomodulatory therapies. METHODS Lung immune complexes were isolated and PAH target antigens were identified by liquid chromatography tandem mass spectrometry, confirmed by enzyme-linked immunosorbent assay, and localized by confocal microscopy. One PAH antigen linked to immunity and inflammation was pursued and a link to PAH pathophysiology was investigated by next-generation sequencing, functional studies in cultured monocytes and endothelial cells, and hemodynamic and lung studies in a rat. RESULTS SAM domain and HD domain-containing protein 1 (SAMHD1), an innate immune factor that suppresses HIV replication, was identified and confirmed as highly expressed in immune complexes from 16 hereditary and idiopathic PAH versus 12 control lungs. Elevated SAMHD1 was localized to endothelial cells, perivascular dendritic cells, and macrophages, and SAMHD1 antibodies were prevalent in tertiary lymphoid tissue. An unbiased screen using metagenomic sequencing related SAMHD1 to increased expression of human endogenous retrovirus K (HERV-K) in PAH versus control lungs (n=4). HERV-K envelope and deoxyuridine triphosphate nucleotidohydrolase mRNAs were elevated in PAH versus control lungs (n=10), and proteins were localized to macrophages. HERV-K deoxyuridine triphosphate nucleotidohydrolase induced SAMHD1 and proinflammatory cytokines (eg, interleukin 6, interleukin 1β, and tumor necrosis factor α) in circulating monocytes, pulmonary arterial endothelial cells, and also activated B cells. Vulnerability of pulmonary arterial endothelial cells (PAEC) to apoptosis was increased by HERV-K deoxyuridine triphosphate nucleotidohydrolase in an interleukin 6-independent manner. Furthermore, 3 weekly injections of HERV-K deoxyuridine triphosphate nucleotidohydrolase induced hemodynamic and vascular changes of pulmonary hypertension in rats (n=8) and elevated interleukin 6. CONCLUSIONS Our study reveals that upregulation of the endogenous retrovirus HERV-K could both initiate and sustain activation of the immune system and cause vascular changes associated with PAH.

中文翻译：

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人类内源性逆转录病毒-K的上调与肺动脉高压的免疫力和炎症有关。

背景技术免疫失调已经与遗传性，特发性或与其他病症相关的肺动脉高压（PAH）中的闭塞性血管重塑有关。循环性自身抗体，肺血管周围淋巴组织和细胞因子升高与PAH的发病机理有关，但对这些异常如何在疾病进展中被引发，永久存在和联系起来还没有一个清楚的了解。因此，我们着手确定PAH肺免疫复合物中的特定靶抗原，作为解决这些问题的起点，以更好地为免疫调节疗法的未来应用提供参考。方法采用液相色谱-串联质谱法分离肺免疫复合物并鉴定PAH靶抗原，并经酶联免疫吸附试验确认。并通过共聚焦显微镜进行定位。寻求一种与免疫和炎症相关的PAH抗原，并通过下一代测序，在培养的单核细胞和内皮细胞中的功能研究以及在大鼠中的血液动力学和肺部研究来研究与PAH病理生理学的联系。结果SAM域和含HD域的蛋白1（SAMHD1）是一种抑制HIV复制的先天免疫因子，已被确认并证实在16种遗传性和特发性PAH相对于12个对照肺的免疫复合物中高表达。升高的SAMHD1定位于内皮细胞，血管周围树突状细胞和巨噬细胞，并且SAMHD1抗体在三级淋巴组织中盛行。使用宏基因组测序进行的无偏筛选使SAMHD1相对于对照肺（n = 4）在PAH中增加了人类内源性逆转录病毒K（HERV-K）的表达。与对照肺相比，PAH中的HERV-K包膜和脱氧尿苷三磷酸核苷酸水解酶mRNAs升高（n = 10），蛋白质定位于巨噬细胞。HERV-K脱氧尿苷三磷酸核苷酸水解酶诱导循环单核细胞，肺动脉内皮细胞以及活化的B细胞中的SAMHD1和促炎细胞因子（例如白介素6，白介素1β和肿瘤坏死因子α）。HERV-K脱氧尿苷三磷酸核苷酸水解酶以独立于白介素6的方式增加了肺动脉内皮细胞（PAEC）对细胞凋亡的脆弱性。此外，