Exogenous HMGB1 exacerbates hypoxia-induced PH via TLR4. WT and Tlr4−/− mice were given daily injections of HMGB1 (10 µg IP) during 10 d of chronic hypoxia and assessed for changes in RVSP (A), RV hypertrophy (B), muscularization of pulmonary arterioles (C, D) and pulmonary arteriolar wall thickness (E). Data represent the mean ± SEM of six mice per group. Analysis of variance: *P < 0.05. n.s., Not significant.