Modulation of serum histamine releasing activity in chronic idiopathic urticaria

Background —Sera of about 30% of patients with chronic idiopathic urticaria (CIU) have increased histamine releasing activity (HRA + ) on normal basophils. It is not known whether other CIU sera would be HRA + if a more sensitive histamine release assay was used. Although most HRA + CIU sera appear to have anti FceR1 activity, it is not known whether post-binding basophil intracellular events are similar to those after anti-IgE stimulation. Results —In the presence of D 2 O, the HR stimulated by 28 previously documented HRA − sera increased from 4±0.4 to 21±4% with 13 of the 28 sera now considered HRA + . No previous HRA − sera was HRA + with IL-3 treated cells. Histamine release induced by both HRA + sera and anti-IgE were inhibited by genistein, and Ca 2+ /Mg 2+ depletion but not by bisindoylmaleimide. HRA + sera induced prominent HR from normal basophils with little surface IgE, but induced no increased HR from basophils unresponsive to anti-IgE. Conclusions —Up to 61% of CIU sera will induce increased HR from normal basophils in a sufficiently sensitive assay system. HR induced by most HRA + sera is more prominent in basophils with very little surface IgE. However, there may be similar post-binding intracellular activation pathways following stimulation by HRA + sera and anti-IgE.