Inhibition of passive sensitization of human peripheral basophils by synthetic human immunoglobulin E peptide fragments.

To delineate the binding site in the human immunoglobulin E (IgE) molecule to the Fc epsilon receptor on basophils and mast cells, we chemically synthesized a total of 71 peptide fragments within the sequence Ser300-Lys547 in the human IgE molecule. The synthetic peptides were tested for their capacity to inhibit passive sensitization of human peripheral basophils with atopic patient's serum containing the specific IgE against dust mites in vitro. It was found that a peptide fragment, Pro345-Ile356, potently inhibited the passive sensitization. To clarify the minimal active core, various analogues, such as shortened, substituted (by Gly or Ala residue), omission and retro-sequence peptides, were synthesized and assayed. The results suggested that the sequence Pro345-Lys352 in the human IgE molecule would be an IgE binding site, and that a synthetic octapeptide, Pro345-Phe-Asp-Leu-Phe-Ile-Arg-Lys352, inhibited the passive sensitization, probably by occupying the Fc epsilon receptor sites on the cells.