Background and aims The process of pulmonary vascular remodelling in pulmonary arterial hypertension (PAH) in systemic lupus erythematosus (SLE) largely depends on migration of pulmonary artery smooth muscle cells (PASMCs). In this study, we tested whether IgG from SLE with PAH have stimulatory effects on PASMC migration.

Methods Sera from 6 SLE patients, including 1 with PAH, and 7 healthy subjects were collected, and IgG was purified using protein A or protein G. PASMC migration was examined by a Boyden chamber method. Lamellipodia formation and antibody binding sites in the cells were examined by immunocytochemistry. Identification of anti-enolase1 antibodies was performed by immunoprecipitation, western blotting, mass spectrometry, and ELISA.

Results IgG from SLE with PAH significantly increased migration of PASMCs than those without PAH in a concentration dependent manner (p<0.001). After incubation with IgG, the number of cells with lamellipodia, which represents rearrangement of the cytoskeleton necessary to migration, was 1.4-fold higher in SLE with PAH than those without PAH (p<0.01). In immunocytochemistry, IgG from SLE with PAH were colocalized with b-tubulin in the cytoplasm of PASMCs, and western blotting showed that the antibodies bound to a˜50 kD protein in the lysates, which was subsequently identified as enolase1 reported to be involved in cell migration. Furthermore, the titer of IgG anti- enolase1 antibodies was 1.5-fold higher in SLE patients with PAH than those without PAH.

Conclusions IgG from a patient with SLE accompanied by PAH promoted a migration of PASMCs, which is possibly ascribed to autoantibodies to enolase1.