Disorders Involving Cytotoxic Antibodies (Type II Reactions) in Dogs
Type II reactions occur when an antibody binds to an antigen present at the surface of its own cells. These reactions can lead to several types of diseases in dogs, including anemia, blood clotting problems, and skin and muscle disorders. They may be associated with other immune system disturbances, such as systemic lupus erythematosus, or triggered by a drug, vaccine, or infection. Most often, the triggering cause cannot be pinpointed. Immune-mediated hemolytic anemia and thrombocytopenia are the most common Type II reactions.
Anemia occurs when an animal has an abnormally low number of red blood cells. Immune-mediated hemolytic anemia is a severe and life-threatening disease in which the dog’s immune system sees its own red blood cells as foreign invaders, and therefore produces antibodies to destroy them. Red blood cells are manufactured as usual in the bone marrow, but once released into the bloodstream, they are attacked and destroyed by antibodies. Signs of anemia may include fatigue, paleness of the lips and gums, and depression, along with jaundice in some cases. Other signs your veterinarian may find include an enlarged liver or spleen.
Immune-mediated hemolytic anemia has 4 basic forms, peracute, acute or subacute, chronic, and cold agglutinin disease. Antibodies against developing red blood cells in the bone marrow can cause pure red cell aplasia, meaning a lack of just red blood cells. Most forms are treatable with medications, including corticosteroids and cytotoxic drugs (such as those often used in chemotherapy). Blood transfusions might be necessary. Relapses are uncommon.
Thrombocytopenia occurs when an animal has an abnormally low number of platelets, which are responsible for blood clotting. When an animal has thrombocytopenia, clotting does not occur correctly. Even minor injuries can cause uncontrollable bleeding, resulting in the loss of red blood cells (anemia). The most frequent signs are bleeding and bruising of the skin and mucous membranes. Immune-mediated thrombocytopenia is common in dogs and occurs more often in females than males. This condition is caused by the destruction of platelets (thrombocytes) by the immune system in much the same manner as red blood cells are destroyed in immune-mediated hemolytic anemia (see above).
Before immune-mediated thrombocytopenia can be diagnosed, many more common diseases must be excluded, including various clotting disorders, infections, cancer, and intestinal parasites. The diagnosis is usually made based on signs and response to treatment, rather than on blood tests. However, certain tests, such as platelet counts, clotting profiles, and bone marrow sampling are helpful. Medication will likely be prescribed to treat this disease. Signs usually disappear after 5 to 7 days of treatment when platelet counts begin to rise. If the platelet count has not increased significantly after 7 to 10 days, additional or different medications may be prescribed. If the blood loss is life threatening, transfusions of whole blood or plasma may be necessary.
Treatment is often continued for 1 to 3 months after the platelet counts return to normal. Some dogs have persistent decreases in platelets even with drug treatment. If this is the case with your pet, you and your veterinarian will want to discuss longterm treatment and maintenance options.
Pemphigus foliaceus is an uncommon autoimmune disease that affects the skin. The cause of this malfunction of the immune system is usually not known. One theory is that the skin is somehow altered, making it appear “foreign” to the immune system. In the case of pemphigus foliaceus, the immune system produces antibodies against the “glue” that normally keeps skin cells (keratinocytes) attached to one another. White blood cells move in causing further damage, and the keratinocytes break apart from each other, forming pimples or crusted areas. Veterinarians frequently prescribe corticosteroids for treatment of pemphigus foliaceus, but other immunosuppressive drugs may be added if there is no response.
Pemphigus vulgaris is a very rare disease in dogs. It produces blisters and sores in and around the mouth and groin, but other areas of the skin are only mildly affected. The disease is often controlled with high doses of corticosteroids in combination with other drugs that suppress the immune system. If untreated, the condition can result in death. Even with treatment, relapses are not uncommon.
Bullous pemphigoid is a rare autoimmune skin disease that is most common in Collies and Doberman Pinschers. Abnormalities are often widespread but tend to be concentrated in the groin. The involved skin resembles a severe scald and may include blisters. The disease is usually treated with corticosteroids and other drugs that target the immune system, but continuous treatment is often needed, and the longterm outlook is poor.
Myasthenia gravis is an autoimmune neuromuscular disease seen in both people and animals, including dogs. It can be congenital (present at birth) or immune-mediated, developing later in life. Weakness is the primary sign. Affected animals produce antibodies to certain nerve receptors and destroy them. This leads to the inability to contract muscles and extreme muscle weakness. In older dogs, the first sign of problems may be an enlargement of the esophagus (megaesophagus) due to the muscular weakness. The enlargement of the esophagus leads to difficulty swallowing and can cause regurgitation, which can cause inhalation pneumonia. Myasthenia gravis is diagnosed using blood tests to search for the antibody to the nerve receptor and other tests for nerve activity. Your veterinarian will prescribe drugs to control this disease. Remissions can occur, and many dogs that develop this condition do well with continued treatment.
Also see professional content regarding Type II reactions.