HMGB1 and persistent fetal circulation syndrome: The serum levels of TNF-α and IL-6 were positively correlated with HMGB1 levels both at PPHN onset (r = 0.832 and 0.866, respectively, P < 0.05) and after remission (r = 0.873 and 0.843, respectively, P < 0.05; Figure 1).