Autoimmunity is a destructive immune response against self antigens Autoimmune diseases are hard to stop Severity ranges from minor to lethal

Some commom autoimmune diseases

Some autoimmune diseases may have a genetic component and are triggered by external factors (e.g., infection) or injury. Others are probably strictly caused by external factors (e.g., infection) or injury

Autoimmune diseases can be organ-specific or systemic

There are 4 types of hypersensitivities: Type 1 refers to allergens that a person may induce or come into contact with in day to day life. Type 2 refers to the hypersensitivity of antigens in red blood cells. Type 3 refers to the reaction of the immune system to foreign antigens. Type 4 refers to antigens that induce a delayed hypersensitivity reaction.

Allergens cause type 1 hypersensitivities. Some examples include:

Herd immunity If enough individuals in a population are immune, infectious disease are not easily maintained or transmitted within the group. Thus, even individuals that are not immune are protected from infection