It is well known that chronic inflammation causes the sarcopenia. Whether the efforts to prevent skeletal muscle loss benefit the immune homeostasis remains unclear. In the present study, the efficacy of leucine supplementation on the maintenance of systemic immune function was evaluated. A sciatic nerve denervation-induced sarcopenic model was established and the volume and thickness of skeletal muscle on the hindlimb were evaluated by magnetic resonance imaging. Oral administration of leucine was carried on for 56 weeks. The skeletal muscle mass and the subsets or function of immune cells were analyzed. 
In leucine-treated sarcopenic mice, skeletal muscle mass on the hindlimb was significantly increased compared to that in non-treated sarcopenic mice. Leucine treatment repaired the mitochondria dysfunction in splenocytes from sarcopenic mice both in vitro and in vivo. In sarcopenic mice, an increase of the PD-1 expression was observed in CD4+ and CD8+ T cells. However, oral leucine administration restored the expression of PD-1 in the lymphocytes to the level of non-sarcopenic mice. 
In conclusion, the administration of leucine exhibits beneficial effects on sarcopenia and may influence the anti-cancer immune responses via adaptive immune resistance mechanism.