This type of reaction occurs when specific types of white blood cells (called T helper cells) respond to antigens and release toxic and inflammatory substances that can damage tissues. Cell-mediated immune reactions can occur in any organ. Treatment usually involves the use of anti-inflammatory drugs and drugs that suppress the immune system, either alone or in combination.

Granulomatous Reactions

Granulomatous reactions are masses of fibrous connective tissue infiltrated by the white blood cells that form a cell--mediated immune response. They occur in some animals following infection with certain types of bacteria or fungi. Although cell-mediated immune responses effectively fight off these infections in most individuals, in a few animals the immune response is only partially effective and results in a mass at the site of infection.

Old Dog Encephalitis

Old dog encephalitis refers to a chronic brain inflammation that can occur in a dog that had distemper many years earlier (also see Disorders Affecting Multiple Body Systems of Dogs: Canine Distemper (Hardpad Disease)). In dogs that have an undetectable infection with the virus, cell-mediated immune reactions may target cells that have been infected by the virus for years.

Contact Hypersensitivity

Contact hypersensitivity results from chemicals reacting with skin proteins. These reactions modify skin proteins in such a way that they are perceived as foreign invaders. The body then produces a cell-mediated immune response against them and causes skin damage. This hypersensitivity usually occurs as a result of contact with sensitizing chemicals incorporated into plastic food dishes, plastic collars, and drugs placed on the skin.

Autoimmune Thyroiditis

Autoimmune thyroiditis is an immune-mediated disease that destroys the thyroid gland. The disease is particularly prevalent in Doberman Pinschers, Beagles, Golden Retrievers, and Akitas. The production of thyroid hormones may be the only detectable sign; however, this condition may occur as part of a broader immune disorder such as lupus, rheumatoid arthritis, or idiopathic polyarthritis (see Immune Disorders of Dogs: Disorders Involving Immune Complexes (Type III Reactions) in Dogs).

Autoimmune Adrenalitis

Autoimmune adrenalitis is caused by infiltration of immune cells into the adrenal glands (located next to each kidney). This causes the destruction of the glands and may lead to the signs of Addison's disease (see Hormonal Disorders of Dogs: Addison's Disease), such as weakness, loss of weight and appetite, diarrhea, and vomiting. It is most common in young, adult female dogs.

Dry Eye (Keratoconjunctivitis Sicca)

Dry eye, or keratoconjunctivitis sicca (see Eye Disorders of Dogs: Dry Eye (Keratoconjunctivitis Sicca)) is caused by an immune reaction that destroys the tear gland. It occurs in dogs, with a genetic predisposition in Cocker Spaniels. Keratoconjunctivitis sicca can follow a viral infection or continuous use of sulfonamides (a type of antibiotic). The disease is treated by giving prescription eye drops that contain cyclosporine, which inhibits the immune response that causes the disorder.

Last full review/revision July 2011 by Christine Andreoni; Kevin T. Schultz, DVM, PhD