Age-dependent increase of IgE-binding and FcepsilonRI expression on circulating basophils in children

Peripheral blood basophils are sparse in the circulation, but they express high-affinity receptors for IgE (FCepsilonRI) and bind IgE efficiently. The present study was performed to elucidate the role of IgE bound on the basophil surface in the development of allergic responses during infancy and early childhood. IgE-binding and FcepsilonRI expression on basophils were evaluated by two-color flow cytometry. Basophil-bound IgE increased rapidly and reached adult levels during infancy in atopic patients, while it gradually increased with advancing age in parallel with serum IgE in normal controls. IgE-binding and FcepsilonRI expression in atopic children were higher than in normal controls among various age groups. They correlated with serum IgE levels but reached a plateau when serum IgE exceeded 300 ng/mL. A low, but significant level of FcepsilonRI expression was observed on cord blood basophils, although IgE-binding was usually undetectable. Incubation of cord blood with IgE rapidly saturated the preexisting IgE receptors and basophil-bound IgE levels increased. When neonatal basophils were cultured for 48 h with IgE, FcepsilonRI expression was upregulated dose-dependently and IgE-binding increased further. The up-regulation of FcepsilonRI was completely inhibited by cycloheximide, indicating that it was dependent on de novo protein synthesis. These results suggest that IgE-binding on basophils serves as a sensitive indicator of allergic sensitization, and that IgE functions as a positive regulator of FcepsilonRI expression in vivo.