In vivo expression of inflammatory cytokine receptors in the joint compartments of patients with arthritis

To test a hypothesis of compartmentalized pathogenesis of different types of arthritis, namely inflammatory arthritis (IA) and osteoarthritis (OA), synovial and cartilage biopsies were examined for the expression of TNF and IL-1 receptors. In cartilage, we found constitutive expression of all receptors in normal tissues, and decreased expression of signal-transducing receptors in pathological chondrocytes. In synovium, there was a lower expression of signal-transducing receptors in cases of OA compared to those of IA. In OA, the three signal-transducing receptors were more abundantly expressed in cartilage, while in IA they were mainly present in synovial tissue (TNFRp75 being expressed more than p55). IL-1 decoy receptor type II was low or absent in synovial tissues, but present in cartilage. The increased expression of TNFRp75 and IL-1RI in OA cartilage, compared to IA, in addition to the abundant local cytokine production, strengthens the hypothesis of autocrine/paracrine action by inflammatory cytokines in the pathogenesis of cartilage damage.