Serologic and molecular characterization of the T15 idiotype--I. Topologic mapping of idiotopes on TEPC15.

The present study was designed to determine the minimum number of idiotopic determinants (Id) comprising the T15 idiotype and to construct a topological map of Id on the TEPC15 immunoglobulin molecule. Seven monoclonal anti-Id antibodies were used to map determinants by solid phase competition radioimmunoassay. The binding of some anti-Id to T15 was inhibited by phosphorylcholine-protein conjugates, while other anti-Id were not, suggesting that these anti-Id bind to different portions of T15 relative to the paratope. In addition, Id were mapped relative to one another in reciprocal competition assays between the anti-Id for binding to T15 coated plates. The topologic relationships between six Id were discerned by this method. A seventh binding site was identical or so close that it could not be discriminated. These studies suggest that the T15 idiotype is composed of at least six discrete overlapping Id whose locations range from the antigen binding region to the CH1 domain on TEPC15.