α-1-Antitrypsin is an endogenous inhibitor of proinflammatory cytokine production in whole blood

Abstract

Several observations suggest endogenous suppressors of inflammatory mediators are present in human blood. α‐1‐Antitrypsin (AAT) is the most abundant serine protease inhibitor in blood, and AAT possesses anti‐inflammatory activity in vitro and in vivo. Here, we show that in vitro stimulation of whole blood from persons with a genetic AAT deficiency resulted in enhanced cytokine production compared with blood from healthy subjects. Using whole blood from healthy subjects, dilution of blood with RPMI tissue‐culture medium, followed by incubation for 18 h, increased spontaneous production of IL‐8, TNF‐α, IL‐1β, and IL‐1R antagonist (IL‐1Ra) significantly, compared with undiluted blood. Dilution‐induced cytokine production suggested the presence of one or more circulating inhibitors of cytokine synthesis present in blood. Serially diluting blood with tissue‐culture medium in the presence of cytokine stimulation with heat‐killed Staphylococcus epidermidis (S. epi) resulted in 1.2‐ to 55‐fold increases in cytokine production compared with S. epi stimulation alone. Diluting blood with autologous plasma did not increase the production of IL‐8, TNF‐α, IL‐1β, or IL‐1Ra, suggesting that the endogenous, inhibitory activity of blood resided in plasma. In whole blood, diluted and stimulated with S. epi, exogenous AAT inhibited IL‐8, IL‐6, TNF‐α, and IL‐1β significantly but did not suppress induction of the anti‐inflammatory cytokines IL‐1Ra and IL‐10. These ex vivo and in vitro observations suggest that endogenous AAT in blood contributes to the suppression of proinflammatory cytokine synthesis.