Here’s a great post from Natural Pet Health Blog;

Autoimmune diseases in dogs follow an almost similar pattern as in humans. Just as autoimmune diseases in humans are suspected to be related to a genetic predisposition, certain breeds of dogs are more vulnerable than others.

The immune system is the body’s internal and natural self-healing system of reciprocation that comes into action as soon it recognizes an intrusion of foreign bodies. We call a disease as immune mediated when some underlying cause has caused the immune system to stop recognizing foreign substances. The immune system stops creating antibodies for combating the invasion and produces an autoantibody that starts destroying normal cells. Such a disease may be restricted to a single organ or region or the whole animal.

Autoimmune diseases have far reaching consequences depending upon the extent to which they have affected the body of the dog. The pathological signs of multiple autoimmune diseases are normally seen in the same animal since the animal becomes more vulnerable to infections due to a weakened immune system. For example, symptoms of liver disease in dogs as well as feline liver disease are common once the immune system’s automatic responses are restricted.

Typically autoimmune diseases occur due to four types of actions that take place within the body:

• An autoantibody targets a specific organ. For example, autoimmune hemolytic anemia occurs when an autoantibody targets blood cells. In Addison’s disease the target is the adrenal gland.
• Antibodies that target different proteins in the body are produced. These circulate through out the body and cause multiple organ autoimmune diseases like systemic lupus erythematosus. Rheumatoid Arthritis is caused by complex immunoglobulin class molecules that are deposited in the lubricating fluid in the spaces between joints.
• Sometimes antibodies and T-cells act together to restrict the activity of an organ. T-cells are one of the two types of cells that carry out an immune response. Autoimmune Hypothyroidism is an example of disease caused through this mechanism. The thyroid receives a large number of T-cells and also antibodies programmed to destroy thyroid cells.
• Autoimmune diseases also arise from deficiencies in the complement system. For example liver disease in dogs restricts production of complement serum enzymes that have to be activated to carry out an immune response.

Due to the innate nature of the disease, autoimmune disease has multiple symptoms that depend upon the organs, body systems that are being targeted. As most of the symptoms tend to confuse and mimic other conditions it requires proper investigation through blood, urine and other tests to confirm whether the condition is immune mediated or not. Some of the symptoms in dogs, reported prior to diagnosis, include:

• Diarrhia and colitis: with or without traces of blood
• Lethargy, Depression and intolerance to exercise
• Muscle wasting and weakness in legs
• Skin sores, mouth ulcers, lesions, especially nasal and anal lesions
• Stiff joints, alteration in gait tending to lameness and stiff limbs
• Enlarged lymph nodes
• Anemia
• Seizures
• Loss of appetite and weight
• Body odor
• A marked change in bark
• Weight gain if thyroid is affected

A weakened immunes system fails to do what it has been programmed to and starts rejecting body’s own tissue as foreign. This exposes a dog to repeated attacks by infections that further deteriorate an already serious condition. It is now coming to light that many well known diseases like Hypothyroidism and Diabetes may be immune mediated and caused by rejection of hormone producing cells.