Chronic Urticaria (CU): is an heterogeneous disease supposed to be due to spontaneous release of histamine from unclarified activation of mast cell or basophil through IgE receptor pathway but treatment targeting either histamine or IgE are not always successful. The aim of this study was to explore Basophil phenotyping and functionality to better classify CU.

Methods: the prospective, clinical study enrolled 31 CU and 29 age and sex matched controls. Basophils were analyzed by flow cytometry.

Results and Discussion: Our CU population demography was very similar to cohorts previously reported. CU were active for 5.58+5.4 years and severe (UAS7 = 25.8+10). Serum IgE were higher than 114kU/L in 36.8% CU vs 12.0% HC. Serum tryptase was higher than 7µg/L in 20%. Basophil represented less than 0.1% of leukocytes in 32.3% CU and even more in case of recent flares. Ex vivo basophil activation was defective in 75.9% of CU vs 31% of HC. However despite an active disease, 41.9% of patients kept a high basophil count and 7 (24.1%) a high reactivity with low serum tryptase and low activation profile suggesting their basophils are not the main effector in the diseases.

Conclusions: Monitoring Basophil count and ex vivo reactivity together with the level of IgE should help in suspecting the basophil and IgE involvement or alternative mechanisms of CU. This could lead to a classification of CU in its heterogeneity and help predicting its response to anti-histaminic or antiIgE therapies.