Evidence of in vivo basophil activation in chronic idiopathic urticaria

Approximately 40% of chronic idiopathic urticaria (CIU) subjects have autoantibodies to FceRIa or to IgE. However, the effect of such autoantibodies on circulating basophil activation status is unclear. We compared the basophils from CIU and allergic subjects for expression of cell surface activation markers. We also examined the serum of donors for histamine releasing activity (HRA) and for immunoreactivity to FceRIa protein. Peripheral blood was obtained from CIU and allergic donors and fractionated by density gradient centrifugation. Enriched basophils (1–8%)were analyzed by flow cytometry for expression of activation markers including CD 69, CD 63, and CD203. Dilutions of serum (5, 25, 50%) were analyzed for HRA on basophils from a single donor. Serum was also tested for immunoreactivity by Western blotting to a standard cell lysate prepared from RBL-SX38 transfected with the human FceRIa. CIU subjects (n=5) demonstrated enhanced expression of all three surface markers as compared to allergic donors (n=5): CD 63, 220 vs. 13.9; CD69, 108 vs. 4.6 and CD203, 4.17 vs. 1.4 (net mean fluorescence intensity units). Three CIU subjects had evidence of significant serum HRA (>20%) on donor basophils. Two CIU donors had evidence of immunoreactivity for FceRIa as compared to none of the allergic donors. The two CIU subjects with both serum HRA and immunoreactivity also had altered basophil function as measured by anti-IgE mediated stimulation. Basophils from CIU subjects express increased levels of activation markers as compared to allergic subjects. Heightened basophil activation in CIU may be due to circulating serum factors.