Anti‐KIF20B autoantibodies in systemic autoimmune rheumatic diseases: Their high prevalence in systemic lupus erythematosus

The kinesin superfamily protein 20B (KIF20B), also known as M‐phase phosphoprotein‐1, is a plus‐end‐directed motor enzyme for cytokinesis. Anti‐KIF20B antibodies have been reported in idiopathic ataxia, but no previous studies have examined anti‐KIF20B antibodies in systemic autoimmune rheumatic diseases (SARDs). We aimed to establish methods for detecting anti‐KIF20B antibodies and to investigate the clinical significance of these antibodies in SARDs. Serum samples from 597 patients with various SARDs and 46 healthy controls (HCs) were included. Fifty‐nine samples that had been examined by immunoprecipitation using the recombinant KIF20B protein produced by in vitro transcription/translation were used for establishing the ELISA cutoff with the same recombinant protein for measuring the anti‐KIF20B antibodies. The ELISA performed well, showing close agreement with the immunoprecipitation results (Cohen's κ >0.8). The ELISA results for 643 samples showed the prevalence of anti‐KIF20B to be higher in the systemic lupus erythematosus (SLE) patients than in the HCs (18/89 vs. 3/46, P = 0.045). Since no SARD other than SLE had higher frequencies of anti‐KIF20B antibodies than those of the HCs, we investigated the clinical characteristics of anti‐KIF20B antibody‐positive cases in SLE. The score on the SLE Disease Activity Index‐2000 (SLEDAI‐2K) was significantly higher for the anti‐KIF20B‐positive SLE patients than for the anti‐KIF20B‐negative SLE patients (P = 0.013). In a multivariate regression analysis of the anti‐single‐stranded deoxyribonucleic acid, anti‐double‐stranded deoxyribonucleic acid, and anti‐KIF20B antibodies, the presence of anti‐KIF20B antibody was significantly associated with high SLEDAI‐2K scores (P = 0.003). Anti‐KIF20B antibodies were found in ~20% of patients with SLE and were associated with high SLEDAI‐2K scores. Much larger cohort and longitudinal studies are needed to confirm the association between anti‐KIF20B antibodies and SLE.