HUMAN RECOMBINANT INTERLEUKIN 4 INDUCES FcER2/CD23 ON NORMAL HUMAN MONOCYTES

Two types of receptors for the Fc portion of human IgE (FccR) have been identified on the surface of human cells. These two types of receptors differ in their affinity for IgE as well as in their cellular distribution and function (1) . Type 1 FcER (FcERI) show high affinity (109/M) for IgE and are detectable on mast cells and basophils (2) . The reaction between allergens and IgE bound to FCERI induces degranulation of basophils and mast cells, with release of chemical mediators responsible for the clinical manifestations of allergy (3) . In contrast, type 2 FCER (FcER2) bind IgE with a lower affinity (10'-10"/M) and are present on monocytes, macrophages, B lymphocytes, platelets, and eosinophils (4) . The binding of IgE to FcER2 on monocytes, eosinophils, and platelets activates a variety of effector functions in these cells (3, 5, 6) . It is well known that the frequency of human peripheral blood monocytes (Mo)' bearing FcER2 is increased in atopic subjects, particularly in the presence of high serum IgE levels, while it is negligible in normal subjects (3) . In addition, it has been recently reported that Mo bearing cytophilic IgE infiltrate into the skin lesions of patients with atopic dermatitis (7) . The role of FcER2+ Mo in the pathogenesis of allergic disorders is, however, still poorly understood . Binding of IgE to FcER2 sensitizes rodent peritoneal (8) and alveolar (9) macrophages to the release of leukotrienes and arachidonic acid upon exposure to allergen . The signals that are able to induce the expression of FcER2 on Mo, however, have not been defined . In the present study, we have examined the ability of a variety of recombinant lymphokines and monokines to induce on human normal peripheral blood Mo the expression of FcER2, as detected by IgE binding . In parallel, we have investigated the ability of the same agents to induce the expression on Mo of the CD23 antigen, as detected by mAb binding . CD23 has been described as a B cell-specific activation antigen (10) and more recently has been shown to be identical to the B cell FcER2 (11, 12) and to the Blast-2 antigen expressed by B cells upon activation by a variety of stimuli (13, 14) . Our data indicate that the expression of FcER2/CD23 by normal human Mo can be spe-