Generation of species-specific, rat monoclonal antibodies that bind to the κ chain of mouse immunoglobulin

Large numbers of mouse monoclonal antibodies (MAbs) with exquisite binding specificities have become available. However the study of these primary antibodies in biological fluids by second, anti-mouse antibody techniques, has been confounded by the large quantity of other animal immunoglobulin which is often present in these fluids. To overcome this problem, we have derived high affinity rat MAbs which bind specifically to the antigen binding fragments (Fab) of mouse antibody and display minimal or no crossreactivity with human or rabbit immunoglobulin at the concentrations which are usually found in plasma. Equilibrium binding studies demonstrated that these antibodies had binding affinity constants for mouse Fab that ranged from 4.3 × 10⁸ to 4.1 × 10⁹ M⁻¹. All of these rat MAbs bound to the κ chain of mouse immunoglobulin, though competition binding studies amongst these MAbs indicated that they probably recognized three different epitopes. Because of their specificity and affinity, these rat anti-mouse κ MAbs may be useful in a wide variety of experimental biological systems both in vitro and in vivo.