HMGB1 levels, TLR4 receptor activity, and HMGB1-dependent TLR4 receptor activity are increased in mice with SCD. (A) Plasma HMGB1 levels in SCD (SS) (hatched bar) compared with control (black bar, n = 9, 11, **P < .01) mice; (B) Plasma-induced total TLR4 receptor activity is increased in SS (hatched bar) compared with control (black bar, n = 6, *P < .05) mice; (C) % HMGB1-dependent TLR4 receptor activity in SS (hatched bar) compared with control (black bar, n = 6, *P < .05) mice; (D) Effect of H/R injury (see Study design) on HMGB1 levels. Left bars: control normoxia (open bar, n = 13) vs control H/R (gray open bar, n = 7) mice; NS, not significant. Right bars: SS normoxia (right-hatched open bar, n = 20) vs SS H/R (left-hatched gray bar, n = 17) mice (*P < .05); (E) Pretreatment of SS mice with isotype control (black bar) or anti-HMGB1 (hatched bar) antibodies did not significantly decrease HMGB1 levels (P = .095, n = 14 to 15); (F) Pretreatment of SS mice with anti-HMGB1 (hatched bar) but not isotype control (black bar) antibodies significantly decreases the ability of SS plasma to induce total TLR4 receptor activity in cultured TLR4 reporter cells (n = 6, *P < .05); and (G) Pretreatment of SS mice with anti-HMGB1 (hatched bar) but not isotype control (black bar) antibodies significantly decreased the % of HMGB1-dependent TLR4 receptor activity in SS plasma (n = 6, *P < .05).