Blood monocytes of untreated asthmatics exhibit some features of tissue macrophages

Airway macrophages are activated in asthmatic subjects. Peripheral blood monocytes from these subjects present some functional features of activation, but their membrane markers are not known. Recently a new subtype of blood monocytes, CD14+/CD16+, has been identified which possesses the characteristics of tissue macrophages. A study was carried out on nine normal subjects and 11 untreated asthmatics having variable severities of the disease to examine the phenotypic characteristics of monocytes. CD14, CD16, HLA-DR, CD11a, CD11b, CD44 and CD54 were studied using double fluorescence flow cytometry since these antigens have been defined in the CD14+/CD16+ monocytes. The functional activation of monocytes was examined using the release of superoxide anion. The co-expression of CD14 and CD16 by monocytes in terms of percentage and mean fluorescence intensity was significantly higher in asthmatics (P < 0.002 and P < 0.0001, respectively, Mann-Whitney U-test). There was no difference for the other membrane markers between asthmatics and normal subjects. Superoxide anion release was significantly increased in asthmatic subjects (P < 0.01). This study shows that most blood monocytes of asthmatics are CD14+/CD16+ and are likely to present features of tissue macrophages.