Blocking of passive sensitization of human mast cells and basophil granulocytes with IgE antibodies by a recombinant human ε-chain fragment of 76 amino acids

The recombinant peptide corresponding to residues 301-376 at the junction of constant regions 2 and 3 of the human IgE ε chain blocked the in vivo passive sensitization of human skin mast cells and in vitro sensitization of human basophil granulocytes with human IgE antibodies. An injection of the recombinant peptide or E myeloma protein into normal skin sites 1 hr before sensitization with an allergic serum blocked passive sensitization. In this system, ~ 10-fold higher molar concentration of the recombinant peptide than E myeloma protein was required for 50% inhibition of Prausnitz-Kustner reactions. When the mononuclear cells of two normal individuals were preincubated with the recombinant peptide or E myeloma protein for 15 min before passive sensitization with the same allergic serum and the cells were challenged with an optimal concentration of an antigen, ~ 11- to 13-fold higher concentration of the recombinant peptide than E myeloma protein was required for 50% inhibition of antigen-induced histamine release. Further studies with several recombinant peptides indicated that amino acid residues 363-376 in the Fc ε-chain fragment are not essential for binding of the peptide to Fc ε-chain receptor I.