There are two distinct receptors for TNF (TNFRs), a 55 kilodalton protein (p55) and a 75 kilodalton protein (p75). The biological activity of TNF is dependent upon binding to either cell surface receptor (p75 or p55). Etanercept is a dimeric soluble form of the p75 TNF receptor that can bind to two TNF molecules, thereby effectively removing them from circulation.
Tumor necrosis factor TNF is a naturally occurring cytokine that is involved in normal inflammatory and immune responses. Elevated levels of TNF are found in tissues and fluids of patients with rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis (AS), and plaque psoriasis. Etanercept binds specifically to tumor necrosis factor (TNF) and blocks its interaction with cell surface TNF receptors.