The effect of platelet-activating factor on IgE binding, to and IgE-dependent biological properties of, human eosinophils.

This study investigated the effect of platelet-activating factor (PAF), leukotriene B4 (LTB4) histamine and formyl-methionyl-leucyl-phenylalanine (FMLP) on immunoglobulin E (IgE) binding and IgE-dependent cytotoxicity of human normal density eosinophils. The binding of a native myeloma IgE to normal human eosinophils was measured by flow cytometry using a fluorescein-conjugated potyclonal anti-IgE antibody. Preincubation with PAF (optimal at 10-7 M), but not lyso-PAF or FMLP, gave dose-dependent increases in IgE binding. PAF and LTB4 gave significant increases in IgE binding after 5 rain preincubation (P < 0·05); the effect was further enhanced at 30 min (P < 0·01). This was further confirmed using the rosette assay where PAF and LTB4, but not lyso-PAF or FMLP, gave dose- and time-dependent increases in IgE eosinophil rosettes. Eosinophil cytotoxicity for schistosomula of Schistosoma mansoni, incubated with immune serum, was also significantly enhanced (P < 0·01) by PAF in a dose-dependent fashion (optimal at 10-8 M). Schistosomula coated with FPLC-purified IgE fractions were susceptible to killing by normal density eosinophils, and this was enhanced with PAF (10-8 M). LTB4 (10-7 M) and histamine (10-5 M) but not with FMLP(10-7 M) or lyso-PAF. IgE-dependent cytotoxicity was confirmed by the removal of contaminating IgG from IgE-rich fractions, and by the abolishment of IgE-dependent cytotoxicity after IgE adsorption. These results suggest that PAF (and to a lesser extent LTB4 and histamine) increase IgE binding, IgE-dependent adherence and cytotoxicity of normal human eosinophils. Although IgE receptors have not been identified, the data support current concepts that certain biological properties of eosinophils may be IgE associated. [ABSTRACT FROM AUTHOR]