given these specific requirements for effective binding, the main application for immobilized protein l is purification of monoclonal antibodies from ascites or cell culture supernatant that are known to have the kappa light chain. protein l is extremely useful for purification of vlκ-containing monoclonal antibodies from culture supernatant because it does not bind bovine immunoglobulins, which are often present in the media as a serum supplement. also, protein l does not interfere with the antigen-binding site of the antibody, making it useful for immunoprecipitation assays, even using igm.