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Find information on animal health topics, written for the veterinary professional.

Disorders Involving Immune Complexes (Type III Reactions) in Cats

By Christine Andreoni, , Senior Manager, Department of Immunology, Discovery Merial Limited
Kevin T. Schultz, DVM, PhD, Chief Scientific Officer, Head of Global Research and Development, Merial Limited

Also see professional content regarding type III reactions.

Immune complex disorders are among the most common immune-mediated diseases. The location in the body where the immune complexes (combinations of antibodies and antigens) are deposited determines the signs and the course of the disease.


Glomerulonephritis is inflammation of the microscopic filtering units of the kidneys known as glomeruli. The inflammation develops when immune complexes become trapped in the glomeruli. This leads to activation of the body’s inflammatory defense system, which, in turn, damages the glomeruli. The immune complexes often form as a consequence of some other disease such as an infection or cancer. However, in many cats with glomerulonephritis, the triggering cause cannot be determined. Glomerulonephritis results in an excessive loss of protein in the urine (proteinuria). The finding of protein in the urine during a urine test (urinalysis) may be the first indication that your cat has glomerulonephritis. Treatment includes giving immunosuppressive drugs to reduce the formation of the immune complexes. If it goes untreated, the disease can lead to chronic kidney failure.

Systemic Lupus Erythematosus (Lupus)

Systemic lupus erythematosus (often simply called lupus) is an autoimmune disease that is rare in cats. Pets with lupus have antibodies in their blood that are targeted against their own body tissues. Lupus causes widespread abnormalities of the skin, heart, lungs, kidneys, joints, nervous system, and blood (anemia and/or decreased platelet numbers). Multiple organs are usually affected. A blood test is the usual method of diagnosing lupus. Longterm treatment with corticosteroids and other drugs that suppress the immune system are prescribed to treat the disorder. Your veterinarian will determine the most appropriate treatment for your pet. (For a more detailed discussion of Systemic Lupus Erythematosus, see Disorders Involving Immune Complexes (Type III Reactions) in Dogs : Systemic Lupus Erythematosus (Lupus).)

Anterior Uveitis

One cause of anterior uveitis (see Disorders of the Anterior Uvea in Cats : Inflammation of the Anterior Uvea) is the action of antibody-antigen complexes on the iris, which causes inflammation of the eye. Uveitis caused by Toxoplasma parasites or by the feline infectious peritonitis virus also has an immunologic basis. Treatment of immune-mediated anterior uveitis may include whole-body corticosteroids and other drugs that suppress the immune system.