The body’s immune system is a host defense system in both people and pets. But I bet you don’t often think about your own immune system. There are several reasons the immune system is harder to wrap your head around than other body systems.
- You hardly know the immune system is there unless it doesn’t work. The immune system’s job is to protect you against invading organisms that might make you sick. If it is working well, you feel great. If it doesn’t work, you get the flu or the chickenpox.
- The immune system is all over your body. The respiratory system seems so obvious. You have a nose, a windpipe and lungs. They control respiration. Bet you can’t describe the location of the cells of your immune system, but they are strewn about in the lymph nodes, spleen, lungs, intestines, and are circulating in your blood stream.
- The immune system can cause serious diseases when immune cells start attacking normal cells. These diseases are classified as autoimmune diseases or immune mediated diseases.
An autoimmune disease is a disease where a hyperactive immune system attacks normal cells as if they were foreign organisms. A diagnosis of autoimmune disease is made when the antibody produced by the abnormal immune function can be identified in the laboratory. Examples of this in people are gluten sensitivity due to an antibody induced by dietary gluten against intestinal cells, or Type 1 diabetes where the immune system makes an antibody that attacks insulin-producing pancreatic cells. Autoimmune diseases are thought to exist in veterinary patients, but tests to confirm the diagnosis are lacking.
Immune Mediated Disease
Immune mediated disease is a disease of unknown cause, but one which is thought to be modulated by an aberrant immune response. Unlike autoimmune diseases, the antibody causing this group of diseases has not been identified. This classification describes several important dog and cat diseases. In dogs and cats, immune mediated hemolytic anemia is an example of an immune mediated disease. Dogs also suffer from immune mediated thrombocytopenia and immune mediated polyarthritis. These diseases target red blood cells, platelets and joints, respectively.
Treatment of Immune Mediated Disease
The key to treatment of immune mediated diseases is to halt the immune reaction underlying the disorder. Veterinarians use immunosuppressive medications to turn off the cells of the immune system. The first line therapy in immune mediated hemolytic anemia, thrombocytopenia and polyarthritis is prednisolone/prednisone, which is a steroid medication. Prednisolone/prednisone receives top billing because it works quickly and is inexpensive. But prednisolone/prednisone is not enough in some cases and a second immunosuppressive agent such as azathioprine, cyclosporine or mycophenylate can be added. Increasing the number of immunosuppressive agents runs the risk of turning off the immune system completely, increasing the risk for a serious infection. Dogs and cats on immunosuppressive agents need close monitoring. Once the immune disease is controlled, the medications are slowly withdrawn and the patient is carefully monitored for relapse.
In future blogs, I will discuss the specifics of some common immune mediated diseases in pets.