Supplementary Material for: The Effect of HMGB1, a Damage-Associated Molecular Pattern Molecule, on Polymorphonuclear Neutrophil Migration Depends on Its Concentration

Polymorphonuclear neutrophils (PMN) play a key role in host defenses against invading microorganisms but also potentiate inflammatory reactions in case of excessive or misdirected responses. Release of the alarmin high-mobility group box 1 (HMGB1) by cells that die at an inflammatory site may act as an alert signal for the immune system. We studied the effect of HMGB1 on human PMN migration, using whole-blood samples to avoid cell activation associated with isolation procedures. HMGB1 50–100 ng/ml reduced baseline PMN migration as well as formyl-methionyl-leucyl-phenylalanine- and IL-8-induced PMN chemotaxis. This inhibitory effect was mediated by the RAGE receptor. In contrast, a higher HMGB1 concentration (5,000 ng/ml) had a chemoattractant effect on PMN through IL-8 production. This effect required the engagement of Toll-like receptors 2 and 4 in addition to the RAGE receptor. The A box component of HMGB1, which antagonizes the endogenous protein, reduced chemotaxis and also strongly inhibited the enhancement of PMN migration observed with the highest HMGB1 concentration. In contrast, the B box, reported to be the active form of HMGB1, exerted a chemoattractant effect. These results strongly point to a key regulatory role of HMGB1 in PMN recruitment to inflammatory tissues. The A box component could potentially serve to inhibit inappropriate PMN recruitment during chronic inflammatory disorders associated with excessive HMGB1 release.