Plasma HMGB1 and anti-HMGB1 antibody levels increase with age in MRL/lpr mice. (A) Plasma HMGB1 levels were measured by Western blot at wks 6, 7, 9, 11, 13, 15 and 17 in MRL/lpr mice (n = 11). HMGB1 levels are presented as values of fluorescence intensity and were normalized against a standard of Jurkat cell lysate. (B) Plasma anti-HMGB levels (ng/mL) were measured by ELISA at wks 6, 7, 9, 11, 13, 15 and 17 in MRL/lpr mice (n = 11). Anti-HMGB1 levels are presented as values of fluorescence intensity and were normalized against a standard of monoclonal anti-HMGB1 antibody.