Three separate epitopes on human IFN-alpha variants defined by monoclonal antibodies and their role in the binding to receptors.

Two monoclonal antibodies (mAbs) designed 9-1-1 and 2-2-1, produced by murine hybridoma clones, raised to recombinant IFN-alpha 2c and one mAb, designed 3A3-2, raised to recombinant IFN-alpha 88, have been characterized with respect to neutralization of IFN antiviral and antiproliferative activities. The regions of IFN molecule which these antibodies are directed against have been defined by analyzing cross- reactivity with four IFN-alpha subtypes (IFN-alpha 88, IFN-alpha 2a, IFN-alpha 2b, IFN-alpha 2c) and two fragments of IFN-alpha 88. An analysis of cross-reactivity patterns with IFN-alpha 88 and IFN-alpha 2c indicated that 3A3-2 mAb was directed to an epitope on IFN-alpha 88 not overlapping with epitopes of other mAbs, however its localization was not exactly defined. The epitope recognized by 9-1-1 mAb was present on IFN-alpha 88 and IFN-alpha 2c, and also was not overlapping the epitopes of other mAbs. Using another variant IFN-alpha 2a, containing Lys instead of Arg at position 23, for competitive binding study it was shown that Arg 23 was implicated in the epitope recognized by 9-1-1 mAb. The competition study with IFN-alpha 88 fragments allowed to locate the epitope recognized by 2-2-1 mAb between amino acid residues 51 and 166. The epitope blocking test indicated that 2-2-1 mAb was directed to an epitope overlapping that of previously reported for mAb NK-2, located around Glu at position 113.(ABSTRACT TRUNCATED AT 250 WORDS)