Inflammation of blood vessels. This may damage their lining and cause narrowing or blockage, thus restricting blood flow. This, in turn, may harm or destroy the tissues supplied by the affected blood vessels. Vasculitis is probably caused by small particles called immune complexes, circulating in the blood, that adhere to the vessel walls and provoke inflammation. Normally these complexes are consumed by the white blood cells. Vasculitis is the basic disease process in several disorders such as POLYARTERITIS NODOSA, ERYTHEMA nodosum, TEMPORAL ARTERITIS and SERUM SICKNESS.