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.
Type II Allergic Reaction. Type II allergic reactions can result from the chemical alteration of antigens present on the surface of some of the cells (like red blood cells) by certain drugs. The alteration in the antigen on the cell surface can result in formation of antibodies (IgG) against these cells and ensuing destruction of the cells.