Characteristics of histamine-releasing activity in the sera of patients with chronic idiopathic urticaria

Background: The serum histamine-releasing activity (HRA) found in a sizable percentage of patients with chronic idiopathic urticaria (CIU) has been partially characterized. However, the variable effect of individual HRA(+) sera in basophils of different donors and the relationship of HRA to the clinical course require further investigation. Objective: The study was performed to characterize the HRA found in sera of some members of a sizable group of carefully evaluated patients with CIU. Methods: Sera of 70 patients with CIU, evaluated with a standard protocol, were screened for increased HRA. HRA(+) sera were fractionated, heated, and tested on unaltered and altered basophils obtained from a panel of normal donors. HRA levels were compared with concomitant clinical manifestations. Results: HRA(+) sera were found in 30% of our patients with CIU. HRA was predominantly in the IgG fraction, sensitive to 56 degrees heating for 4 hours, and generally reacted more with IgE-stripped basophils. Considerable variation in the degree of response to HRA(+) sera in the basophils of different normal subjects did not correlate with the degree of response of these cells to heterologous anti-IgE antiserum. Serum HRA levels were generally much lower when symptoms decreased in these patients with CIU. Conclusion: Serum HRA from patients with CIU appears to bind most commonly to the IgE receptor and may be a marker of clinical disease activity. HRA appears in an IgG-containing fraction of the serum and may contain IgE in some cases.