Interleukin-15: a muscle-derived cytokine regulating fat-to-lean body composition.

An increasing body of literature links immune and inflammatory factors to modulation of growth and control of fat:lean body composition. Recent progress in understanding the control of body composition has been made through identification of inflammatory cytokines and other factors produced by adipose tissue that affect body composition, often by direct effects on skeletal muscle tissue. Adipose-derived factors such as leptin, tumor necrosis factor-alpha, resistin, and adiponectin have been shown to affect muscle metabolism, protein dynamics, or both, by direct actions. This review summarizes recent results that support the existence of a reciprocal muscle-to-fat signaling pathway involving release of the cytokine IL-15 from muscle tissue. Cell culture studies, short-term in vivo studies, and human genotype association studies all support the model that muscle-derived IL-15 can decrease fat deposition and adipocyte metabolism via a muscle-to-fat endocrine pathway. Fat:lean body composition is an important factor determining the efficiency of meat production, as well as the fat content of meat products. Modulation of the IL-15 signaling axis may be a novel mechanism to affect body composition in meat animal production.