Detection of basophil-activating IgG autoantibodies in chronic idiopathic urticaria by induction of CD63

Approximately 40% to 50% of patients with chronic idiopathic urticaria (CIU) have functional IgG autoantibodies against FcɛRIα or IgE, which induce histamine release from basophils and cutaneous mast cells. A positive autologous serum skin test response is believed to reflect the presence of these autoantibodies. We sought to further define the functional properties of and develop a sensitive functional assay for detection of autoantibodies in patients with CIU. Sera from patients with CIU (n = 61) and sera from healthy control subjects (n = 23) were incubated with donor basophils. Activation of basophils was determined on the basis of CD63 surface expression, as analyzed on a FACScan flow cytometer. A positive basophil activation test result was found in 51% of patients with CIU, and basophil-activating properties were present in the IgG fractions of sera. When both the in vitro test and the autologous serum skin test were considered, basophil/mast cell–activating autoantibodies were present in 62% of the patients. Patients with a positive basophil activation test result had a significantly higher prevalence of other autoantibodies, had more severe urticaria, and were more likely to have angioedema. The results demonstrate the presence of basophil-activating autoantibodies in about 50% of patients with CIU. The data support the autoimmune cause of the disease and provide a simple test for detection of these autoantibodies.