Relationship between changes in the 7-day urticaria activity score after treatment with omalizumab and the responsiveness of basophils to FcεRI stimulation in patients with chronic spontaneous urticaria

BACKGROUND: About one-half of all patients with chronic spontaneous urticaria have low or less reactivity of the basophils to FcεRI stimulation. However, the differences in the clinical characteristics between patients who show normal and attenuated basophil reactivities to FcεRI stimulation are still unclear. Furthermore, it also remains unknown as to what factors induce the poor reactivity of basophils to FcεRI stimulation. OBJECTIVE: The aim of the study is to investigate the differences in the clinical characteristics between patients who show normal and attenuated basophil reactivities to FcεRI stimulation. METHODS: We compared the clinical characteristics, including the autologous serum skin test-positive rates, serum concentrations of anti-IgE and anti-FcεRIα autoantibodies, and the FcεRI-crosslinking ability of these autoantibodies between patients with a negative basophil activation test (BAT) (≤10% CD203c(high) basophils, n = 9) and positive BAT (>10% CD203c(high) basophils, n = 13). We also monitored the changes in the 7-day urticaria activity scores after treatment with omalizumab, as compared to the score at the baseline, between the BAT-positive and BAT-negative patients. RESULTS: The BAT-negative patients showed a significantly higher urticaria control test score than the BAT-positive patients (p = 0.01). There were no significant differences in the autologous serum skin test-positive rates, concentrations of anti-IgE and anti-FcεRIα autoantibodies, and the FcεRI-crosslinking ability of these autoantibodies between the 2 groups. After treatment with omalizumab for 35 days, the score decreased to under 15 (corresponding to controlled or mild chronic spontaneous urticaria) in all of the BAT-negative patients, whereas in 6 out of the 13 BAT-positive patients, the scores remained over 16 (corresponding to moderate or severe chronic spontaneous urticaria). CONCLUSIONS: The weak reactivity of basophils to FcεRI stimulation may not be due to the desensitization of basophils by anti-IgE or anti-FcεRIα autoantibodies. The time to response to omalizumab might differ between BAT-negative and BAT-positive patients with chronic spontaneous urticaria.