Characterization of functional domains of human interferon gamma by specific monoclonal antibodies

For the study of functional domains of hIFNgamma, two MABs were characterized. Both MABs, named 1E11 and 5D6, were sequence-specific for hIFNgamma. According to the estimated additivity index, they recognized epitopes located at distinct non-overlapping areas of the hIFNgamma molecule. When pre-incubated with hIFNgamma, MAB 1E11 was able to neutralize the antiviral as well as the antiproliferative activity of the cytokine. This indicated that MAB 1E11 was specific either for the domain responsible for binding to the cell receptor or for a domain required for both functions. By contrast, the second MAB 5D6 did not interfere with any of the two hIFNgamma biological activities. The epitope of MAB 5D6 was located between the amino acid residues Leu 135 and Glu 143 by using different forms of C-terminally truncated hIFNgamma. These data allow the conclusion that the last nine C-terminal amino acids are not essential for the receptor binding and biological functioning of this cytokine. The possible role of hIFNgamma C-terminus in the intracellular cascade of events is discussed.