Circulating basophils in patients with type IIb autoimmune chronic spontaneous urticaria have a lower histamine content

Abstract Background Patients suffering from chronic spontaneous urticaria (CSU) are typically classified as type I or type IIb autoimmune CSU, but further patient stratification is hindered by the lack of biomarkers. Objectives We investigated whether the histamine content of individual basophils differ between patient subtypes in CSU to evaluate its potential as a biomarker. Methods A total of 101 patients diagnosed with CSU were included in the study. The histamine content per circulating basophil was derived from the basophil count in peripheral blood and levels of total cellular blood histamine. These measures, together with results from the serum‐induced basophil histamine release assay (s‐BHRA), were correlated to information on demographics, clinical characteristics, patient reported outcomes and laboratory analyses. Results The histamine content per basophil was significantly different between s‐BHRA positive and ‐negative patients (0.175 vs. 1.40 pg/cell, p < 0.001) and showed a significant negative correlation to the degree of basophil activation in s‐BHRA ( ρ = −0.209, p = 0.036). Furthermore, the amount of histamine in individual basophils was found to be significantly correlated with levels of total cellular blood histamine ( ρ = 0.376, p < 0.001), eosinophil counts ( ρ = 0.205, p = 0.040), levels of thyroid stimulating hormone ( ρ = −0.246, p = 0.014) and titre of antibodies against thyroid peroxidase ( ρ = −0.216, p = 0.031) and thyroglobulin ( ρ = −0.203, p = 0.044). Conclusions Low content of intracellular histamine in circulating basophils is associated with known markers of type IIb autoimmune CSU. Further studies are required to assess whether the amount of histamine in basophils can be used to monitor or predict response to treatment in patients.