Elevated levels of OPN are found in plasma or serum and tissue specific fluids of patients suffering from several granulomatous disorders including tuberculosis and silicosis [23,24], and from Th-1 related disorders such as inflammatory bowel disease [25,26], systemic lupus erythematosus [27], certain types of multiple sclerosis [28,29] and rheumatoid arthritis [30]. Here, SPP1 is linked to rheumatoid arthritis.