Antihistamines do not inhibit the flare induced by the intradermal injection of autologous plasma in chronic urticaria patients

Background : there is some evidence suggesting that factors other than autoantibodies to FceRI or IgE and histamine released from mast cells may play a role in skin autoreactivity that characterizes many patients with chronic urticaria (CU) and, possibly, in the pathogenesis of this disease. Objective : the effect of antihistamine treatment on autologous plasma skin test (APST) in patients with CU was assessed. Methods : 24 patients with CU underwent autologous plasma skin test (APST) as well as SPT with histamine 10 mg/ml while taking antihistamines. In 6 cases the same tests had been carried out also before the start of antihistamine treatment. Plasma levels of Ddimer, prothrombin F1+2 fragment, and vascular endothelial growth factor (VEGF) were measured in 21 patients. Results: 21/24 (87%) patients showed a large flare on APST while taking antihistamines while the skin reaction to histamine 10 mg/ml was abolished or negligible. Little difference in the autologous plasma-induced flare was seen before and after the start of cetirizine therapy in 6 cases, whereas the drug exerted a marked effect on the histamine SPT as well as on the autologous plasma-induced wheal. The APST-induced flare was not associated with patients’ response to antihistamine. Plasma levels of VEGF, prothrombin F 1+2 fragment, and D-dimer were increased in plasmas from 8, 9, and 2 patients, respectively. Conclusions : factors other than histamine are probably involved in the flare following APST in CU; such factors might play a pathogenic role particularly in patients not responding to standard antihistamine treatments