HMGB1 is a nuclear protein that acts as an early mediator of inflammation and organ damage in hepatic ischemia-reperfusion (I/R) injury, unlike its role as a late mediator in sepsis. The study shows that HMGB1 levels increase in the liver as early as 1 hour after reperfusion and rise further over 24 hours. Neutralizing HMGB1 with an antibody significantly reduces liver damage and inflammation, while recombinant HMGB1 worsens injury. The protective effect of HMGB1 neutralization is associated with reduced phosphorylation of JNK and increased NF-κB DNA binding. TLR4-defective mice show less liver injury and do not benefit from HMGB1 neutralization, suggesting TLR4 is involved in HMGB1 signaling. The study demonstrates that HMGB1 acts as an early mediator of I/R injury through TLR4, highlighting its role in inflammation and tissue damage. These findings suggest that targeting HMGB1 could be a therapeutic strategy for ischemic liver injury and other inflammatory conditions.HMGB1 is a nuclear protein that acts as an early mediator of inflammation and organ damage in hepatic ischemia-reperfusion (I/R) injury, unlike its role as a late mediator in sepsis. The study shows that HMGB1 levels increase in the liver as early as 1 hour after reperfusion and rise further over 24 hours. Neutralizing HMGB1 with an antibody significantly reduces liver damage and inflammation, while recombinant HMGB1 worsens injury. The protective effect of HMGB1 neutralization is associated with reduced phosphorylation of JNK and increased NF-κB DNA binding. TLR4-defective mice show less liver injury and do not benefit from HMGB1 neutralization, suggesting TLR4 is involved in HMGB1 signaling. The study demonstrates that HMGB1 acts as an early mediator of I/R injury through TLR4, highlighting its role in inflammation and tissue damage. These findings suggest that targeting HMGB1 could be a therapeutic strategy for ischemic liver injury and other inflammatory conditions.