HMGB1 and systemic sclerosis: To further assess the relationship between serum calpain activity and HMGB1 in the pathogenesis of SSc, we evaluated whether serum calpain activity was correlated with serum HMGB1 level and found that serum calpain activity was correlated positively with HMGB1 level (r = 0.3891, p < 0.05; Fig. 2g).