Hemoglobin stimulates the release of proinflammatory cytokines from leukocytes in whole blood

Isolated mononuclear leukocytes, when incubated with purified hemoglobin Ao (HbAo), release the proinflammatory cytokines interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-alpha). In this study we examined whether leukocytes in whole blood, when incubated with HbAo, release IL-8, TNF-alpha, and IL-6. Leukocytes in whole blood incubated with HbAo for 4 hours at 37 degrees C, 5% CO2, and 95% humidity released 187, 1313, and 50 pg/mL of IL-6, IL-8, and TNF-alpha, respectively as compared with 6, 192, and 2 pg/mL released by leukocytes in blood incubated with human serum albumin (HSA). Furthermore, plasma from blood incubated with HbAo exhibited chemotactic activity and stimulated human umbilical vein endothelial cells to become adherent to neutrophils. These activities were 3.3 and 2.6 times those measured in plasma from blood incubated with HSA. Hydrocortisone (0.05 mu mol/L to 50 mu mol/L) inhibited cytokine release in a dose-dependent manner with ED50 values of 0.23 mu mol/L, 0.19 mu mol/L, and 0.10 mu mol/L for IL-6, IL-8, and TNF-alpha, respectively. The release of proinflammatory cytokines in whole blood after exposure to hemoglobin solutions is consistent with the possibility that an inflammatory reaction could develop on infusion of hemoglobin, whereas inhibition of cytokine release by hydrocortisone suggests that the inclusion of anti-inflammatory compounds in hemoglobin solutions may prevent undesirable effects caused by inflammation after infusion.