Increased sensitivity of eosinophils for eosinophilopoietic cytokines in atopic dermatitis

Despite normal concentrations of serum eosinophilopoietic cytokines, blood eosinophilia was noted in patients with atopic dermatitis (AD) (n = 32). Significant increase of EG2+ "activated" eosinophil numbers that are mirrored in serum eosinophil cationic protein (ECP) levels in vitro, though not always in synchrony with total eosinophil counts, was also demonstrated. Functionally, AD-source eosinophils showed an enhanced MCLA-dependent chemiluminescence (MDCL) responsiveness to the eosinophilopoietic cytokines, with the characteristics that interleukin-5 (IL-5)-induced MDCL responses strongly correlated with EG2+ eosinophil proportions, whereas both IL-3- and granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced MDCL responses rather significantly correlated with the degree of blood eosinophilia. Like other eosinophil-associated parameters (total eosinophil counts, EG2+ eosinophil counts and serum ECP levels), those cytokine-induced eosinophil MDCL responses significantly increased in correlation to the AD severity. These results suggest that i) eosinophilopoiesis accompanying development of both IL-3- and GM-CSF-sensitive eosinophils within the bone marrow, and induction of IL-5-sensitive/EG2-reactive eosinophils in the periphery may be regulated through inflammatory events in AD lesional skin; ii) it is unlikely that these eosinophil in vivo differentiation may be due to direct effect of locally synthesized three eosinophilopoietic cytokines; and iii) enhanced sensitivity of EG2+ eosinophils for IL-5 may be responsible for elevated levels of serum ECP in vitro.