CD14 and rheumatoid arthritis: MMP-2, also known as gelatinase A, is one of the key members of a family metalloproteases that are capable of cleaving gelatins; collagen types I, IV, and V; elastin; and vitronectin and is expressed in CD14+ CD68+ monocytes and macrophages that infiltrate the synovial tissue of patients with rheumatoid arthritis [36].