Background The basopenia of chronic urticaria relates to histamine releasing autoantibodies in the serum of patients with autoimmune urticaria. This reduction in circulating basophils may be due to active recruitment into weals. If so, it might be expected that numbers in blood would be reduced when urticaria is active and increased after treatment. The primary aim of this study was to look at diurnal variation of basophil numbers in patients with chronic ordinary urticaria (not physical or vasculitic) in relation to disease activity and the effect of treatment with antihistamines and corticosteroids, and to compare the results with healthy controls. A secondary aim was to compare a standard manual counting method with automated basophil counts and to look at numbers of other circulating leucocytes that might be relevant to urticaria pathogenesis.
Methods Manual basophil counts using a toluidine blue stain and automated 5-part differentials (Coulter® Gen. S™) were performed at 4-hourly intervals from 08.00 to 20.00 in 10 healthy controls (six women, age 24 to 63 years) and seven chronic urticaria patients (five women, 24 to 50 years). All chronic urticaria patients had severe daily or almost daily urticaria. Only one of six chronic urticaria sera showed in vitro basophil histamine releasing activity. Counts were performed without treatment, after a week of taking loratadine 10 mg daily and after 3 days of adding prednisolone at 0.6 mg/kg/day (maximum 40 mg). Daily urticarial activity scores (UAS) were derived from weal numbers and itch, maximum 7.
Results There was no significant overall diurnal variation of basophil numbers in healthy controls or chronic urticaria patients. Mean (SE) manually counted basophil were higher in healthy controls than chronic urticaria (43.4/µL (2.1) vs. 4.4 (0.8), P < 0.001). Basophil counts were reduced in healthy controls on steroids (19.2 (1.9), P < 0.001) but increased in chronic urticaria (8.9 (1.9), P < 0.001). Loratadine did not influence them. UAS fell on treatment (3.3 (0.4) baseline, 1.4 (0.5) on loratadine and 0.5 (0.2) on prednisolone with loratadine, P < 0.001). There was a negative linear correlation between basophil numbers and UAS in untreated chronic urticaria patients (P = 0.001, Spearman rank correlation). Manual and automated basophil counts showed poor agreement. Lymphocyte numbers were lower in chronic urticaria than healthy controls. Neutrophils increased whereas lymphocytes and eosinophils decreased in all subjects on prednisolone. They were unaffected by loratadine.
Conclusion The results are consistent with the hypothesis that circulating basophils may be recruited from blood into urticarial weals during disease activity. Automated counts are not suitable for assessing basophil numbers in chronic urticaria. The relevance of reduced lymphocyte numbers in chronic urticaria needs to be explored.