Although it is unknown what causes most types of vasculitis, immune system abnormality, inflammation of blood vessels, and genetic factors appear to be somewhat important in the cause of the disease. Vasculitis can also be caused by an immune or allergic reaction in the vessel walls.
Allergic reaction: The hypersensitive response of the immune system of an allergic individual to a substance. When an allergen enters the body, it causes the body's immune system to develop an allergic reaction in a person with an allergy to it. This reaction can occur when the immune system attacks a normally harmless substance (the allergen). The immune system calls upon a protective antibody called immunoglobulin E or IgE to fight these invading substances.
An allergic response is a hypersensitive immune reaction to a substance that normally is harmless or would not cause an immune response in everyone. An allergic response may cause harmful symptoms such as itching or inflammation or tissue injury. Allergies are an abnormal immune reaction. The human immune system is designed to protect the body from potential harm and in people who have allergies the immune system will react to allergens (substances that trigger an immune response). The immune system will produce immunoglobulin E, IgE, antibodies for each allergen.