Induction of Histamine Release and Desensitization in Human Leukocytes

Protein A from Staphylococcus aureus has been found to react with all human leukocyte preparations tested. In 70%, of the experiments the reaction leads to histamine release. Further more, protein A treatment of cells at 37°C both in complete and Ca +2 ‐free medium, results in the inhibition of anti‐IgE‐induced histamine release in all cell preparations, indicating that protein A and anti‐IgE antibodies release histamine from the same cells. This inhibition seems to be due to the blocking or exhaustion of a step in the biochemical pathway, leading to histamine release activated by both protein A and anti IgE. In some cell preparations desensitization but no histamine liberation is induced by protein A. No inhibition occurs if the protein A treatment is performed at 4°C. It is concluded that protein A elicits histamine liberation and desensitization by acting on IgG present on the surface of the basophil granulocytes Treatment of leukocytes at 37°C with anti‐IgE antibodies, or F(ab') 2 fragments from such antibodies, also results in an inhibition of a subsequent anti‐IgE‐induced histamine release. Desensitization with low doses of anti‐IgE results in an inhibition of the same type as that obtained with protein A. Supraoptimum amounts of anti‐IgE or high amounts ill monovalent Fab fragments from anti‐IgE immunoglobulin G give an inhibition that could be due to a competition between the sensitizing and the challenging agents for combining with cell‐fixed IgE molecules This inhibition is independent of temperature and calcium concentration.