1 mab - 2 different proteins?

[Whitnall]

This a very real possibility - MABs often demonstrate high
affinities for completely unrelated proteins because of the
fact that only one epitope is being recognized. See
Nigg, E.A., Walter, G. and Singer, S.J. On the nature of 
crossreactions observed with antibodies directed to defined 
epitopes. Proceedings of the National Academy of Sciences, USA 
79: 5939-5943, 1982.
- Mark