Analysis of antigenic domains on natural and recombinant human IFN-beta by the inhibition of biologic activities with monoclonal antibodies.

Human IFN-beta (HuIFN-beta) is a biologically potent protein with both antiviral and antiproliferative activities. To understand better its mode of action, a number of murine mAb were developed against a recombinant (serine-17) HuIFN-beta (rHuIFN-beta ser) and screened by ELISA and neutralization of antiviral activity. The panel of antibodies, composed of both IgA and IgG immunoglobulins, were specific for HuIFN-beta and did not crossreact with HuIFN-alpha or gamma. Furthermore, three functionally distinct epitopes (designated as sites I, II, and III) were identified based on mAb neutralization of antiviral and antiproliferative activities of recombinant and natural HuIFN-beta. Antibodies directed to sites I and II neutralized the antiviral and antiproliferative activities of rHuIFN-beta ser, though the antiviral neutralization potency of the mAb to site II was approximately 10-fold less than mAb to site I. Antibodies directed to site I neutralized both recombinant and natural HuIFN-beta, although the antiviral neutralization potency was approximately 10-fold higher against rHuIFN-beta ser than the native protein. The mAb directed to site II did not demonstrate any significant neutralization of the antiviral or antiproliferative activity of natural HuIFN-beta but neutralized a recombinant HuIFN-beta containing the native sequence. Antibodies recognizing site III did not neutralize the biologic activity of either recombinant or natural HuIFN-beta. Thus, three epitopes on HuIFN-beta have been identified, two of which are associated with both antiviral and antiproliferative activities.