CCP, or anti-cyclic citrullinated peptide antibodies, are a group of autoantibodies that are often associated with autoimmune diseases, particularly rheumatoid arthritis (RA). These antibodies target a specific type of protein called citrullinated peptides, which are found in the joints of individuals with RA. Citrullination is a post-translational modification of proteins in which the amino acid arginine is converted to citrulline.