Vaso-occlusion and hyperalgesia induced by cold exposure are ameliorated by blocking C5 activation or C5aR signaling. (A) HbSS mice (n = 4 per group) were implanted with DSFC windows. At baseline, flowing subcutaneous venules (20-23 venules per mouse) were selected and mapped. After baseline selection of flowing venules, mice were injected IV via the tail vein with control, anti-C5 mAb, or anti-C5aR mAb (1.2 mg/kg). Thirty minutes after mAb infusion, mice were exposed to cold at 10°C (50°F) for 1 hour and then returned to RT. Microvascular stasis (vaso-occlusion) was measured at the indicated times after return to RT. Values are means ± SEM. ∗∗P < .01 and ∗P < .05, anti-C5 or anti-C5aR mAb vs control mAb (2-way ANOVA with the Tukey multiple comparison test). (B) Baseline PWT was measured in the hind paws of HbSS mice using von Frey filaments. After baseline pain measurements, nonhyperalgesic mice (PWT > 0.7) were injected IV via the tail vein with control mAb, anti-C5 mAb, or anti-C5aR mAb (n = 4 mice per group; 1.2 mg/kg). Thirty minutes after mAb infusion, mice were exposed to cold at 10°C (50°F) for 1 hour and then returned to RT. PWT was measured at the indicated times after cold exposure. (C) In experiments without cold exposure, HbSS mice that had ongoing hyperalgesia (PWT < 0.7) during baseline testing were injected IV via the tail vein with control mAb or anti-C5aR mAb (n = 6 per group; 1.2 mg/kg). PWT was measured at the indicated times after mAb infusion. (B-C) Values are means ± SEM. ∗P < .05 control mAb vs anti-C5 or anti-C5aR mAbs (2-way ANOVA with the Tukey multiple comparison test). ^#P < .05, ^##P < .01, and ^###P < .001 vs baseline (2-way ANOVA, with the Dunnett multiple comparison test).