Histamine releasing activity of blood mononuclear cells is acquired by means of activation of mast cells.

It has been shown that peripheral blood mononuclear cells (PBMC) obtained from atopic patients with acute clinical manifestations of pollinosis, atopic dermatitis or bronchial asthma, and preincubated in vitro for 18 hours, acquired the ability to induce histamine release from auto-basophils and basophils of healthy donors. Both PBMC and their supernatants possessed this histamine releasing activity (HRA). During remission, HRA could be reproduced in sensitive patients after positive cutaneous tests with a specific allergen. Skin tests with non-specific allergen or histamine-induced provocations were ineffective. HRA of PBMC was also reproduced in healthy individuals after pronounced Prausnitz-Küstner reactions or compound 48/80-induced inflammatory responses. It is concluded that the in vivo activation of mast cells (MC) might be responsible for the acquirement by PBMC of the potential ability to induce histamine release and that this ability was realized after in vitro incubation of such prepared PBMC.