Cytophilic IgE on human blood and tissue eosinophils: detection by flow microfluorometry

Flow microfluorometry (FMF) was used to investigate the presence of cytophilic Ig (IgE or IgG) and the proportion of Fc receptor (Fc epsilon R or Fc gamma R)-bearing eosinophils among eosinophils from 21 hypereosinophilic patients. In a large majority of the cases, it was possible to detect cytophilic IgE significantly associated with serum IgE levels. Moreover, when lung and blood eosinophils were compared, the proportion of occupied Fc epsilon R was significantly increased on lung eosinophils, whereas very few cells had cytophilic IgG. This work provides further evidence that cytophilic IgE is not restricted to cells with high affinity Fc epsilon R, but can also be detected on the cell populations with low affinity IgE receptors. These findings support the view that eosinophils can act as effector cells in immediate hypersensitivity reactions and in diseases associated with increased IgE production and hypereosinophilia.