Nutritional compositions having dietary nucleotides, ∞-3 fatty acids and citrulline are provided. The nutritional compositions may be formulated to improve T cell function, increase arginine availability in vivo, regulate myeloid-derived suppressor cells ("MDSC"), and decrease the risk and/or severity of infection after surgery or trauma. Methods of making, using and administering such nutritional compositions to individuals in need of same are also provided. Methods for modulating the affects of MDSC"s are also provided.
