Reduced HBsAg positivity in systemic lupus erythematosus and Sjögren's syndrome: A retrospective comparative study.

Background: Systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) are two common systemic autoimmune diseases. Recent studies have suggested that the prevalence of hepatitis B surface antigen (HBsAg) may be lower in patients with SLE compared to the general population; however, the existing evidence remains limited and controversial. A systematic analysis of HBV infection rates and serological marker distributions in patients with SLE and SS may offer important insights into the interaction between autoimmune and antiviral immunity. Methods: We retrospectively analyzed 2421 hospitalized patients with SLE and 2049 with SS at Nanjing Drum Tower Hospital from January 2019 to December 2024. Patients with other autoimmune diseases (including rheumatoid arthritis (RA), ankylosing spondylitis (AS), ulcerative colitis (UC), and Crohn's disease (CD)) and 5927 non-autoimmune hospitalized patients were included as controls. Hepatitis B virus (HBV) serological markers (HBsAg, HBsAb, HBeAg, HBeAb, and HBcAb) and anti-HCV antibodies were tested. We compared the positivity rates of HBV seromarkers across different groups and performed subgroup analyses based on sex, age, and autoantibody profiles. Results: The HBsAg positivity rate was significantly lower in SLE and SS patients compared with non-autoimmune controls (1.2 % vs. 5.2 %, P < 0.0001; 1.7 % vs. 5.2 %, P < 0.0001, respectively). No significant differences were observed in patients with RA, AS, UC, or CD. Stratified analyses revealed consistently lower HBsAg positivity in SLE and SS patients across both sexes and all age groups above 20 years. Further analyses indicated that this phenomenon was not attributable to occult HBV infection, inpatient versus outpatient status, or immunosuppressant use. Notably, high ANA titers and the presence of antibodies such as anti-dsDNA, anti-SSA, and anti-ribosomal P were associated with lower HBsAg positivity. No significant differences in HBsAg positivity were found between patients with or without common complications. Conclusion: SLE and SS patients exhibit consistently lower HBsAg positivity rates, independent of clinical factors, and linked to autoantibody status. These findings suggest disease-specific immune mechanisms that may promote HBV clearance or reduce susceptibility to infection.