Allergen-Mediated Histamine Release from Whole Blood

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Abstract
An automated spectrofluorometric histamine assay has been applied to the study of allergen-mediated histamine release on small samples of blood. Histamine released into the plasma following incubation of blood with grass pollen, house dust or cat dander was compared in 35 nonallergic controls and 43 atopic patients sensitive to these allergens by history, skin tests and a high RAST score. 14 of the patients suffering from hay fever were examined after completion of at least 1 year of preseasonal immunotherapy. No allergen-mediated histamine release was observed in most nonallergic controls; a negligible release (< 5% of total blood histamine) was seen in about 10% of these subjects. In contrast, a significant histamine release, ranging from 6 to 48% of total blood content, was specifically induced by allergen in over 90% of patients sensitive to it. Negative results are found more frequently in atopic patients submitted to immunotherapy. In some patients, allergen-mediated histamine release on whole blood was compared to that obtained with the corresponding isolated leukocytes. As expected, a good correlation was found between both systems but anaphylactic histamine release occurs much more quickly in the blood than in the leukocyte suspension. This procedure for measuring histamine released by antigen on blood is easy to perform. Heparinized blood may be stored 48 h without modification in the anaphylactic release of histamine and eight different allergens may be tested with 10 ml of blood. It thus appears to be a useful method for exploring reaginic hypersensitivity and may function as an in vitro alternative to skin tests.