Dissociation of IgE from receptors on human basophils. I. Enhanced passive sensitization for histamine release

Leukocytes of only 1 of 11 nonatopic donors could be passively sensitized for histamine release elicited by ragweed extract. A short incubation in an unbuffered isotonic saline at pH 3.9 or in an 0.01 M lactic acid/lactate-buffered isotonic saline at pH 3.9 dissociated from 4 x 10⁵ to less than 3 x 10⁴ IgE molecules per basophil from washed leukocytes of several in a series of 6 atopic and 11 nonatopic donors. After such treatment, leukocytes of only 1 of the 11 nonatopic donors could not be sensitized for histamine release. Basophils of the 4 ragweed-sensitive donors lost their sensitivity to ragweed after the treatment, but all could be passively resensitized; for 3 of these donors the level of release approximated their original reactivity. Leukocytes of the 2 mold-sensitive donors could be passively sensitized to ragweed allergens after but not before treatment. Four plasma samples from histamine release-positive volunteers were used for sensitization of treated leukocytes of each cell donor; 3 were consistently effective and 1 was consistently ineffective. The positive plasmas had concentrations of antigen E-specific IgE of over 100 ng/ml, which accounted for 17 to 23% of the total IgE; the inactive one had less than 5 ng/ml of specific IgE. For each cell donor, all 3 samples of active plasma mediated quite similar histamine release, but there was a spectrum of donor cell reactivity ranging from 23 to 70% release. These results suggest that basophils from each donor, atopic or nonatopic, had a maximal potential for in vitro sensitization, which was only attained if the plasma contained appropriate, but yet to be fully defined, concentrations of specific and total IgE. Several unexpected results were obtained. Treated leukocytes from some individuals were sensitized for mediator release to a greater extent by sixfold diluted than undiluted plasma. In addition, a 4-hr incubation with plasma at 37°C, but not at 25°C or 0°C, was less effective than were shorter incubation periods. Treated leukocytes should be useful in studying kinetic and equilibrium parameters of IgE binding to specific receptors on human basophils. Analogous treatments should also be useful in sensitization and measurement of IgE-receptor interaction of mast cell populations.