Secreted Semaphorin 5A Activates Immune Effector Cells and Is a Biomarker for Rheumatoid Arthritis

Objective. To investigate the role of the multifunctional protein semaphorin 5A (Sema5A) in modulating cellular immune responses and as a biomarker in rheumatoid arthritis (RA). Methods. A soluble form of recombinant Sema5A was used to assess its effect on the functions of primary T cells and natural killer (NK) cells isolated from the peripheral blood of healthy donors. Cell proliferation and expression of transcription factors were determined by flow cytometry. Cytokine secretion was analyzed using Luminex technology. Serum samples obtained from 145 patients with RA and control serum samples obtained from healthy individuals or patients with non-RA rheumatic diseases were analyzed for the presence of secreted Sema5A, using enzyme-linked immunosorbent assays and immunoblotting. Results. Soluble Sema5A strongly increased T cell and NK cell proliferation and induced the secretion of proinflammatory Th1/Th17 cytokines. Accordingly, Sema5A stimulation caused significant up-regulation of T-bet and retinoic acid receptor-related orphan nuclear receptor gamma t levels in T cells. In addition, significantly elevated levels of secreted Sema5A were detected in the serum of patients with RA compared with control se-rum. Sema5A levels were highest in patients with RA who were positive for the RA biomarker anti-cyclic citrullinated peptide (P < 0.001 versus patients with systemic lupus erythematosus and patients with Sjogren's syndrome) and correlated with the levels of rheumatoid factor. Conclusion. Soluble Sema5A is a potent activator of T cells and NK cells in vitro, and high serum levels of Sema5A are associated with RA. Taken together, the results indicate that Sema5A contributes to the pathogenesis of RA through antigen-independent T cell and NK cell activation. Hence, Sema5A is a promising complementary biomarker for the diagnosis of RA.