Overview of Immunologic Diseases in Animals

The function of the immune system is the detection and destruction of invading microorganisms and abnormal cells. Because of the great diversity of microbial invaders, the immune system is a complex mixture of protective mechanisms. These may be simply classified as innate immunity and adaptive immunity. Immediate protection within the first few hours and days of microbial invasion is the responsibility of the “hardwired” innate immune system. Longer-term protection is the responsibility of the adaptive immune system.

In general, immune system disease takes three forms:

• insufficient immune function causing immunodeficiencies, manifested as increased susceptibility to infections

• excessive immune function, resulting in inappropriate cell and tissue damage or hypersensitivities

• autoimmune diseases, in which the immune system directly attacks normal body cells and organs.

Some inflammation and limited tissue destruction are features of the normal innate and adaptive immune responses. Clinical disease occurs when this inflammation is excessive, in the wrong place, or directed against the wrong target.