Isolation and identification of a biologically active peptide derived from the CH3 domain of human IgG1.

A 24-amino acid residue peptide has been isolated from the Fc region of a human IgG1 myeloma protein. The peptide has associated with it the same ability to induce murine B cells to polyclonally secrete antibody as does the intact Fc fragment. Amino acid composition of the peptide indicates that on a mole/mole basis the isolated peptide is identical to that published for residues 335-358 in the Eu IgG1 sequence. This peptide corresponds roughly to the first 24 amino acids of the CH3 domain. It is believed that the immunoregulatory properties that have been ascribed to the Fc fragment are associated with this peptide.