Determination of a distinguished interferon gamma epitope recognized by monoclonal antibody relating to autoantibody associated immunodeficiency

Anti-interferon gamma autoantibodies (anti-IFN-γ autoAbs) neutralize the IFN-γ-mediated functions, contributing to immunodeficiency. A particular autoAb in patient serum had been previously demonstrated to recognize the same determinant on IFN-γ as the neutralizing anti-IFN-γ monoclonal antibody clone B27 (B27 mAb). This study explored the epitope recognized by B27 mAb. The specific peptide sequence recognized by B27 mAb, TDFLRMMLQEER, was retrieved from a phage display random peptide library. Sequence alignment and homology modeling demonstrated that the queried phage peptide sequence and structure were similar to amino acids at position 27–40 (TLFLGILKNWKEES) of the human IFN-γ. This determinant resides in the contact surface of IFN-γ and interferon gamma receptor 1. To elucidate the crucial amino acids, mutations were introduced by substituting T27 and T27F29L30 with alanine or deleting the amino acid residues T27–L33. The binding of B27 mAb to IFN-γ T27A using western blotting was lesser than that to wild-type. The interaction with triple mutant and T27–L33 deletion mutant using western blotting and sandwich ELISA was abolished. The finding demonstrated that T27, F29, and L30 are critical residues in the B27 antigenic determinant. Identification of the functional domain of IFN-γ decrypted the relevance of neutralizing autoAb in adult-onset immunodeficiency.