You probably haven't read too much about interleukin-15 (IL-15), In fact, I'd surmise that you've never even heard of this protein. What is IL-15? This relatively newly discovered cvtokine is involved in numerous physiologic processes. Cytokines -
a class of molecules that are important in coordinating local and whole-body inflammatory responses can be produced by numerous cells, including monocytes and lymphocytes (both are types of white blood cells), as well as other nonlymphoid tissue.
This protein is best known for its role in immune function; for instance, it has been shown to improve the immune function of patients with an HIT infection. In addition, IL-15 is a growth factor. In a study in which IL-15 was injected into mice, scientists found that it stimulated angiogenesis, or the formation of new blood vessels. But perhaps even more interesting is its potential anabolic effect on skeletal muscle. In a study using immature muscle cells or myoblasts in tissue culture, researchers examined the effects of IL-15 on myosin heavy-chain appearance anti myohiast reproduction. Myoblasts are the earliest forms of a muscle fiber. IL- 15 was found to cause a five-fold increase in myosin heavy-chain (the primary component of your muscles contractile machinery accumulation as well as the formation of myotuhes (developing muscle fibers) that were larger than the controls, An intriguing follow-up experiment was undertaken to determine if IL-15 could affect a I ready altered myotubes (immature muscle fibers). When IL-15 was compared to insolinhke growth factor-1 (IGF-1), IL-15 was found to he as effective as IGF-1 in stimulating the appearance of myosin heavy-chains, and the combination of IGF-1 and IL-15 had a synergistic effect on myosin heavy chain production.
At this point, the regulation of skeletal muscle protein by cytokines isn't completely understood. For instance, some catabolic cytokines (EL 1 and IL-h) have been found to increase in aged humans and mice. IL-I formation also increases in chronic wasting. In hone, a tissue similar to muscle in that its mass is regulated by a balance between synthesis and degradation, IL-4 and IL-5 have been found to inhibit osteoclasts (cells involved in bone breakdown), while EL-i and IL-fl stimulate osteoclast activity. Thus, IL-i and IL-h have similar catabolic roles in muscle and hone.
The exact role of IL-15 in skeletal muscle is unclear, It seems to affect a wide variety of tissues; nonetheless, some evidence suggests that this unique cytokine may be a useful agent in stimulating muscle hypertrophy or alleviating muscle atrophy.