Treatment of Rheumatoid Arthritis with Biological Agents

Cytokines and Rheumatoid Arthritis The term “cytokine” is coined from the combination of “cyto”, a prefix which means cell, and “kine”, which denotes movement. Cytokines all have the following features: 1. They are low-molecular-weight glycoproteins that are not hormones. 2. They have an effect at very small concentrations. 3. Different cytokines can have the same function (redundancy). For example, both tumor necrosis factor (TNF) and interleukin-6 (IL-6) have synovial prolif‐ eration activity and destroy articular cartilage and bone. 4. One cytokine can act on various organs at the same time (pleiotropy). For example, TNF causes synovial proliferation, destroys articular cartilage, and promotes fever. 5. Each cytokine has a specific receptor and acts by binding to that receptor. Inflammatory cytokines play a central role in rheumatoid arthritis. In the treatment of rheu‐ matoid arthritis with biological agents, the effects of cytokines are suppressed by blocking the cytokine from binding to its specific receptor (Figure 1). With respect to these cytokines, antibodies and antibody fusion proteins that inhibit the ac‐ tion of IL-1, IL-6, and TNF have already been commercialized, and development of an IL-17 inhibitor is underway (Figure 2,Table 1).