rProtein L from Peptostrepto coccus magnus binds immunoglobulins (Ig) primarily through kappa light chain interactions without interfering with the antigen binding site of Igs. Specifically it has been shown to bind strongly to human kappa light chain subclasses I, III, and IV and also to most kappa chains from other species such as rat and mouse. This recognition of certain kappa light chains means that rProtein L can bind to a wider range of Ig classes and sub-classes from a variety of species than any other commercially available Ig binding protein.