# Autoimmunity

The human body is equipped with a sophisticated mechanism to preserve the body against a variety of invading organisms. In some disease states, this mechanism is focused against some of its own elements, which cause harm. This group of diseases are called 'autoimmune'. Some diseases are autoimmune in nature, for example, Rheumatoid arthritis and Lupus erythematosus.

## Autoimmunity in domestic animals

The immune system has the capacity to control possible reactions against its own antigens by means of central and peripheral regulation. Autoimmunity appears when the regulation of the immune response is not working well. During central tolerance lymphocytes, T and B are induced in apoptosis if they recognize the body antigens as strange.
Autoimmunity is a kind of hypersensitivity in which the immune system recognizes the body´s components as strange antigens. It can be mediated by lymphocytes B, T, antibodies or a combination of both. Other possibilities are when antigens are hidden by biological barriers or some microorganisms have similarities with body antigens.
There are a few factors such as genetics, breed, species or the breeding system which can predispose autoimmunity in domestic animals. For example, genetics is not decisive but it can increase problems in these diseases, but it is not enough to induce autoimmunity by itself. Some dog breed in which cross-breeding is highly endogamic, risks are increased because in these cases the most important reason could be less genetic variability; this happens especially in immunodeficiencies. On the other hand, we can see molecular mimesis between heart muscle or neuron antigens and some antigens of microorganisms like Trypanosoma cruzi.
There are four types of hypersensitivity, but the following are the most frequent examples. In cows, IgE synthesis is induced when α-casein of milk has access to the bloodstream and after second exposure animals develop anaphylaxis. Hashimoto´s thyroiditis is common in dogs and chickens but in general it is not poliglandular like in humans. It can affect only one organ. Some breeds like Dobermann, Great Dane, Cocker Spaniel, Beagle are commonly affected by this disease. Gland thyroid appeared with lymphocytes and plasmatic cells including germinal centers. Cytotoxic cells, antibodies, and complement cause lysis. Clinical signs such as hypotrichosis, dry hair, pyoderma, hyperpigmentation develop when 75% of the gland is destroyed. The same mechanism occurs in newborn hemolytic anemia in horses when the mother and father have different blood groups. Myasthenia gravis can affect dogs, cats and human beings, it is characterized by fatigue and muscle weakness after exercise. In breeds such as Fox Terrier, Jack Russell Terrier, and Springer Spaniel this disease is hereditary and congenital. Clinical signs appear in young dogs but in adult dogs, it is caused by IgG antibodies against acetylcholine receptors and they cause damage with complement. Drugs such as anticholinesterase enzymes are useful in the treatment.
Diabetes mellitus, which is rare in cattle but most common in dogs, is a disease mediated by antibodies against an enzyme of pancreatic islets (β cells). The mechanism is possible through antibodies, cytotoxic cells or both. In veterinary medicine the treatment must be immunosuppression.