Osteoimmunology is a new subject which focuses on the communication between the immune
and the skeletal systems. Both the immune system and bone communicate with each other. Proinflammatory
cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) play
important roles in immune responses and bone metabolism. TNF-α and IL-6 enhance macrophage activation
and antigen presentation, as well as regulating immunity through different mechanisms.
A variety of groups have reported that TNF-α suppresses osteoblasts activity at some stages of differentiation
and stimulates osteoclast proliferation and differentiation. In contrast, IL-6 mediates the actions
of osteoblasts and osteoclasts through sophisticated mechanisms, which reflect dual effects. Both
TNF-α and IL-6 can mediate the activity of osteocytes. Furthermore, both TNF-α and IL-6 are important
pathogenic factors related to immune-mediated bone diseases including rheumatoid arthritis and
postmenopausal osteoporosis. This review will discuss the contradictory findings concerning TNF-α
and IL-6 in osteoimmunology and their potential for clinical application.