The present invention provides antibodies and fragments thereof that specifically detect the complex of a specific cognate antigen-binding moiety, in particular antibodies, and its antigen. The antibodies of the present disclosure do not bind either said cognate antigen binding moiety or said antigen alone and thus can be used e.g. to directly detect antigen-bound antigen-binding moieties. Further disclosed are methods for use of said antibodies and antibody fragments.