despite this wide binding range, protein l is not a universal antibody-binding protein. protein l binding is restricted to those antibodies that contain kappa light chains. in humans and mice, most antibody molecules contain kappa (κ) light chains and the remainder have lambda (λ) light chains. protein l is only effective in binding certain subtypes of kappa light chains. for example, it binds human vκi, vκiii and vκiv subtypes but does not bind the vκii subtype. binding of mouse immunoglobulins is restricted to those having vκi light chains.