Inhibition of IgE binding to tissue culture cells and leucocytes by pentapeptide

The specific binding of radiolabelled IgE to a tissue culture lymphoblastoid cell line (Wil-2WT) was confirmed. The binding of IgE and Hamburger's IgE-derived pentapeptide Asp-Ser-Asp-Pro-Arg (HEPP) to Wil-2WT cells and to human leucocytes was compared. HEPP inhibition of IgE binding to leucocytes averaged 24% but with Wil-2WT cells only 12% inhibition was observed with double the amount of HEPP. Using myeloma IgE to inhibit the binding of tritiated HEPP to leucocytes and Wil-2WT cells confirmed the specificity of the peptide binding as well as the greater affinity of HEPP for leucocytes (basophils) compared to Wil-2WT lymphoblastoid cells. Based upon the extent of binding and the maximum inhibition attainable with HEPP it is suggested that the receptors for IgE on Wil-2WT cells, basophilic leucocytes and mast cells are not identical but that they share specificities in common. A new hypothesis for the mechanism of action of HEPP is proposed.