Anti-HMGB1 antibody is a potential characteristic autoantibody for Sjögren's syndrome

Sjögren's syndrome (SS) is a common chronic inflammatory autoimmune disease that affects about 0.33–0.77% population in China. The positive for antinuclear antibodies (ANA) is one of the key features of SS, which shows a nuclear fine speckled (AC-4) pattern in an indirect immunofluorescent antibody test (IIFT). About 70% of ANA-positive SS patients have detectable anti-SS-A and/or SS-B antibodies, which indicates that other autoantibodies may present in SS patients. The anti-HMGB1 antibodies in 93 SS patients and 96 healthy controls were investigated with in-house developed ELISA and immunoblotting, and the locations of HMGB1 and fluorescent pattern of anti-HMGB1 antibody were investigated with IIFT. The contribution of anti-HMGB1 antibody in ANA-IF was evaluated with Cas9-induce HMGB1 knockout B16 cells. The anti-HMGB1 antibody level is higher in SS patients (9.96 ± 5.55 RU/ml) than in healthy controls (4.9 ± 1.4 RU/ml). With ROC curve analysis, when taking 8 RU/ml as the cutoff value, the sensitivity, specificity, and the area under the curve were 64.5%, 96.9%, and 0.83, respectively. A total of 18 patients (20.7%) with nuclear fine speckled (AC-4) pattern in ANA-IF test were anti-HMGB1 antibody positive only. With commercial antibody, anti-HMGB1 antibody showed the same nuclear fine speckled (AC-4) pattern. The serum from ANA-IF (+), SS-A (−), and SS-B (−) SS patients showed nuclear fine speckled (AC-4) pattern in wildtype B16 cells, but no fluorescence in HMGB1 knockout B16 cells. Anti-HMGB1 antibody may be one of the characteristic autoantibodies of SS in addition to anti-SS-A and SS-B. The detection of anti-HMGB1 antibody can provide more laboratory evidence for clinical diagnosis of SS.