Enhancement of the histamine releasing activity of mouse monoclonal anti-human IgE antibody xb6-16 when present in aggregated or complexed forms.

FPLC purification of mouse monoclonal anti-human IgE antibody xb6-16 showed 2 major peaks of different molecular weight, peak 1 (greater than 10(6) d) and peak 3 (1.6 x 10(5) d). Peak 1 consisted of IgG1 and IgM, peak 3 of IgG1 only. On a protein weight basis, peak 1 was 100 times more potent than peak 3 in inducing histamine release from human basophils. Preincubation of peak 3 with anti-IgG1 enhanced the mediator release triggered by this fraction. On this basis, the potentiating effect of aggregated IgG1 or IgG1-IgM complexes on mediator release from basophils is discussed.