Elevated levels of the soluble form of bone marrow stromal cell antigen 1 in the sera of patients with severe rheumatoid arthritis

Objective. Bone marrow stromal cell antigen 1 (BST-1) is a novel glycosyl phosphatidylinositol-anchored ectoenzyme, which is overexpressed on bone marrow stromal and synovial cell lines derived from patients with rheumatoid arthritis (RA). To investigate the pathophysiologic roles of BST-1 in RA, we established an enzyme-linked immunosorbent assay (ELISA) system to detect the soluble form of BST-1 (sBST-1) and examined levels of sBST-1 in the sera of RA patients. Methods. Concentrations of sBST-1 in sera from healthy donors and from patients with RA, osteoarthritis, Sjogren's syndrome, and systemic lupus erythematosus were measured with the ELISA. Results. In 7% of the RA patient samples (10 of 143), concentrations of serum sBST-1 were higher (similar to 30-50-fold) than in non-RA samples. Serum sBST-1 concentrations showed no correlation with age, C-reactive protein level, or rheumatoid factor level. All RA patients with high concentrations of serum sBST-1 had severe disease with involvement of several large joints. Conclusion. We believe the measurement of serum sBST-1 may have prognostic value, but further analysis is necessary to clarify the clinical significance of elevated sBST-1 in RA.