HMGB1 and macrophage activation syndrome: All our studied MAS patients expressed serum ferritin levels that followed a parallel temporal course to that of plasma HMGB1 levels (Figs. 2, 3, 4 and 5a) and all these parameters mirrored the clinical course with decreased levels after etoposide administration coinciding with clinical improvement (Figs. 2, 3, 4 and 5b).