The study of immune responses to the environment. Its main clinical applications include: improving resistance to microbial infections (see IMMUNITY); combating the effects of impaired immunity (see IMMUNODEFICIENCY); controlling harmful immune reactions (see ALLERGY); and manipulating immune responses (see IMMUNOTHERAPY) to prevent harmful immunological responses such as graft rejection and autoimmune diseases (see AUTOIMMUNITY). The clinical study of disordered immunity now forms the allied discipline of clinical immunology, which is closely linked to the laboratory-based discipline of immunopathology.