Carbon monoxide modulates the response of human basophils to Fc εRI stimulation through the heme oxygenase pathway

Abstract

We report the effects of exogenous and endogenous carbon monoxide (CO) on the immunological activation of human basophils. Hemin (1−100 μM), a heme oxygenase substrate analogue, significantly increased the formation of bilirubin from partially purified human basophils, thus indicating that these cells express heme oxygenase. This effect was reversed by preincubating the cells for 30 min with Zn-protoporphyrin IX (100 μM), a heme oxygenase inhibitor. Hemin (100 μM) also decreased immunoglobulin G anti-Fc ε (anti-IgE)-induced activation of basophils, measured by the expression of a membrane granule-associated protein, identified as cluster differentiation protein 63 (CD63), and by histamine release. These effects were reversed by Zn-protoporphyrin IX (100 μM), by oxyhemoglobin (HbO 2), a CO scavenger (100 μM), and by 1 H-[1,2,4]oxadiazolo[4,3- a] quinoxalin-1-one (ODQ), an inhibitor of the soluble guanylyl cyclase (100 μM). Exposure of basophils to exogenous CO (10 μM for 30 min) also decreased their activation, while nitrogen (N 2) was ineffective. HbO 2 and ODQ reversed the inhibition, reversing both membrane protein CD63 expression and histamine release to basal values. Both hemin and exogenous CO significantly raised cGMP levels in basophils and blunted the rise of calcium levels caused by immunological activation. This study suggests that CO increases cGMP formation, which in turn induces a fall in intracellular Ca 2+ concentration, thereby resulting in the inhibition of human basophil activation.