Both allergies and autoimmune diseases are characterized by an overactive immune system that can irritate or damage its host’s own tissues in response to an antigen invasion within the body.
For example, atopic (allergic) dermatitis in dogs and cats results from an overactive immune response to inhaled pollens. Lupus erythematosus and pemphigus are two autoimmune disorders that, aside from causing significant skin lesions, can damage other organs of the body as well.
With autoimmune hemolytic anemia, the immune system actually destroys the body’s own red blood cells, leading to anemia. Myasthenia gravis, a disease characterized by profound muscle weakness after only minimal exertion, is also classified as an autoimmune disease.
Immunity mediated kidney disease and arthritis can also afflict pets stricken with a genetic predisposition for these disorders. Many cases of hypothyroidism in dogs are caused by an overactive immune system attacking and inactivating the thyroid hormone produced within the body.
Finally, in cats, the classic example of an immune system gone awry is feline infectious peritonitis. In this disease, it is not the virus itself but rather the exaggerated immune response to it that actually proves fatal to the cat.
Allergies and most autoimmune reactions can be controlled with corticosteroid medication, which, at high enough dosages, has a suppressive effect on the immune system.
However, because these steroids can have significant side effects, such treatments should only be performed under the close, continual supervision of a veterinarian.