Intracellular events in anti-IgE nonreleasing human basophils

Histamine release (HR) after activation of human basophils with anti-IgE demonstrates a great variability among different donors. To elucidate the biochemical basis of this phenomenon, we studied the activation of purified basophils from donors that barely demonstrated HR (<7%) after stimulation by anti-IgE, although IgE was present on these cells and formyl-methionyl-leucyl-phenylalanine (fMLP)-induced HR was normal. Basophils from anti-IgE "nonreleasers" demonstrated, in contrast to cells from "releasers", hardly any changes in cytosolic-free Ca⁺⁺ concentration after addition of anti-IgE. However, anti-IgE treatment of basophils from these anti-IgE nonreleasers resulted in at least two intracellular changes. First, a profound inhibition (54.2%±4.2%) of a subsequent fMLP-induced HR was observed. This inhibition caused by anti-IgE was also observed in basophils from anti-IgE releasers treated with wortmannin, an inhibitor of the anti-IgE-induced HR. The time course of the inhibition induced by wortmannin plus anti-IgE on the fMLP-induced HR (half-life maximum, 4 minutes; time of maximum concentration, 10 minutes) was comparable to the time course of the anti-IgE-induced HR. Second, anti-IgE did induce homotypic aggregation in these anti-IgE-nonreleasing basophils, like in anti-IgE-releasing basophils. These studies indicate that basophils not responding to anti-IgE with HR or cytosolic-free Ca⁺⁺ concentration changes do generate intracellular signals that inhibit the subsequent response to a heterologous stimulus and induce homotypic aggregation.