Immune systems include  specialized  organs like lymphatic tissue, bone marrow, tonsil and spleen which produce  materials such as antibodies (Ads) to fight with foreign materials like virus or bacteria.

Antibody: is a specialized molecule which is build by immune system to fight with foreign materials like bacteria.Every foreign material has a unique protein which is recognized by Ab.

Antigen:The unique protein of every cell is named antigen (Ag) .The source of antigen can be internally or externally but in normal condition immune system can recognize internal antigen and it doesn’t reaction to it.Immune system has this ability to recognize Ag and build its  Ab against it.It means every Ag has its own Ab.

When a body is attacked by Ags , immune system as a defense mechanism sends Abs to fight with them to prevent from infection.In this process Ab attaches to Ag and this reaction leads to produce Ag-Ab complex.This complex provokes some messenger systems in the body to attract specialized cells like white blood cells to that area to surround the Ags.This reaction leads to congestion and pain .For this reason when a lesion is occurred in the skin, injured area is painful, inflamed and red.

As it was mentioned immune system has this ability to recognize internal Ags.If not,this system starts to builds autoantibodies against internal Ags. This reaction leads to autoimmune disease.On the basis of the reaction of immune system to Ags of internal organs clinical signs of involved tissues can be seen in dogs or cats.These organs can be blood,skin, joint, muscle, kidney and  eye. Immune reaction to these organs causes hemolysis, dermatitis, arthritis, myositis , Renal failure and  uveitis respectively. Certain breeds are more prone to autoimmune diseases.

Unfortunately there is no sharp treatment for autoimmune diseases but with special medication they can be controlled.Needless to say  diagnosis as soon as possible has better prognosis with treatment.