Radioiodination of human interferon-α2 interferes with binding of C-terminal specific antibodies

Abstract

Radioimmunoassays based on reactivity between a monoclonal antibody (mAb) and human 125I-interferon (IFN)-α2 are frequently exploited in interferon research. In general, epitopes of antibodies specific for human IFN-α2 are located on the two immunodominant structures formed in the N- and C-terminal domains, respectively. We found that labelling of IFN-α2 with Na 125I by the chloramine-T method did not affect the binding of antibodies recognising the N-terminal region 30–53. In contrast, radioiodination of IFN was associated with a dramatic decrease in IFN reactivity with mAbs specific for the C-terminus (residues ∼120–145∼). We suggest that steric hindrance araising from the incorporation of 125I into the tyrosine residues at positions 123, 130 and 136 may be responsible for the change in immunoreactivity. The adverse effect of radioiodination of IFN-α2 on the binding potency of C-terminal specific mAbs must be taken into consideration in experiments based on the interaction of such antibodies (i.e. NK2) with the labelled antigen.