Interleukin-1 and Naproxen Down-Regulate the Expression of IL-1 Receptors in Cultured Human Rheumatoid Synovial Cells (HRSC)

Using affinity binding of [125I]-IL-1 alpha and Scatchard analysis, we demonstrate here that exposure of cultured synovial cells (HRSC) to NPX (10(-4) M) for 96 h decreased the binding of IL-1 by 20 to 35%. This effect results from a down-regulation of the IL-1 receptors without change in the apparent binding affinity (kD: 770 pM). Pretreatment of cultures with IL-1 alpha (500 pg/ml) reduced the total binding of [125I]-IL-1 alpha on HRSC by 65%, indicating that IL-1 decreases the expression of its own receptors.