An antineutrophil cytoplasmic antibody (ANCA) is a protein produced by the body's immune system, and it is associated with a number of different diseases. The protein is considered to be an autoantibody because it indicates that the body's immune system is attacking itself. Whether a person has an ANCA present in his blood is determined with a commonly performed diagnostic test that is indicated when patients are having certain symptoms. The two different types of ANCAs, c-ANCA and p-ANCA, are associated with diseases such as Wegener's granulomatosis, microscopic polyarteritis, Churg-Strauss syndrome, and polyarteritis nodosa.
Antibodies are proteins produced by the immune system that work to fight against threats to the body. For example, if a person is exposed to a virus, his or her body might start producing antibodies that will bind to this pathogen and help facilitate its elimination from the body. Sometimes the immune system dysfunctions and begins to produce antibodies against components of its own body, and these are referred to as autoantibodies. The antineutrophil cytoplasmic antibody is one of these autoantibodies, as it represents the body attacking its own neutrophils, which are white blood cells that are important parts of the body's defenses.
Whether a person is producing an antineutrophil cytoplasmic antibody can be evaluated by checking a sample of the blood. Often the antibodies are broken down into two classes, the central ANCA (c-ANCA) and the peripheral ANCA (p-ANCA). Distinguishing between these two classes depends on a laboratory study that localizes what part of the neutrophil the antibody is attacking. Patients who have c-ANCA have antibodies attacking the central regions of neutrophils, typically because the antibodies are attacking a substance called proteinase-3. Those with p-ANCA have antibodies targeting myeloperoxidase, which is a substance located in the outer regions of these neutrophils.
A number of different diseases are associated with having an antineutrophil cytoplasmic antibody. The presence of c-ANCA is most closely associated with a condition called Wegener's granulomatosis, a disease in which the body attacks medium-sized blood vessels throughout the body. Symptoms associated with this disease can be varied, but can include cough, kidney failure, lung disease, muscle pain, fever, and weight loss.
The finding of having a positive peripheral antineutrophil cytoplasmic antibody is associated with a few different autoimmune diseases. It is associated most strongly with conditions called polyarteritis nodosa, Churg-Strauss syndrome, and microscopic polyarteritis. These three diseases are all forms of vasculitis, which is the generic term for a condition associated with inflammation of the body's blood vessels.