False-positive signals in enzyme immunoassay (EIA) interactions between rodent IgG subclasses

Interactions between mouse and rat monoclonal antibodies (MAbs) in EIA have been detected using panels of mouse and rat MAbs of various isotypes. Mouse and rat antibodies of the IgG2a subclass were found to bind to each other most strongly. Immobilised IgG1 antibodies of the two species showed much less interaction. Rat IgG2b and IgG2c were intermediate in binding activity. We were unable to study examples of mouse IgG2b and IgG3 MAbs. By making use of the kappa light chain allotype in the rat we were also able to show intraspecies interactions of rat MAbs with the IgG in rat serum. The molecular basis of these interactions has not been resolved but may involve the extended hinge region and flexible Fab arms of the IgG2a subclass of Ig permitting strong inter domain bonding between the constant region domains of adjacent molecules of this isotype.