HMGB1 and systemic lupus erythematosus: Anti-HMGB1 antibodies were positive in only three out of 24 patients (12.5%) with active AAV, in a median titer (OD: 0.465; range: 0.442 to 0.556) lower than in the two SLE patients included as positive controls (0.592 and 0.659, respectively).