Dietary Arginine Supplementation Does Not Enhance Lymphocyte Proliferation or Interleukin-2 Production in Young and Aged Rats

Recent studies indicate that supplemental arginine may enhance in vitro hymphocyte mitogenesis. To determine whether dietary arginine could reverse age-associated losses in immune functions, we fed purified amino acid diets to young (2-mo-old) and aged (24-mo-old) Fischer 344 rats. Rats receiving control (1.12% arginine) or supplemented (3% arginine) diets were pair fed to intakes of deficient (0% arginine) rats. Another group was fed the supplemented diet ad libitum. On d 15, responses of splenocytes to phytohemagglutinin (PHA), concanavalin A (Con A), and pokeweed mitogen (PWM) were lower (P < 0.01), but interleukin-2 (IL-2) production was higher (P < 0.05) in aged rats than in young rats. At mitogen doses producing maximal stimulation, supplemental arginine did not enhance PHA-, Con A- or PWM-stimulated lymphocyte proliferation; PWM responses at sub-maximal doses were higher in pair-fed supplemented rats than in control or ad libitum supplemented rats (P < 0.05). Arginine supplements did not increase thymus weights or IL-2 production above controls. In another experiment, weanling rats received control and supplemented diets in amounts equal to the intake of deficient rats for an average of 37 d. Splenocytes were cultured with mitogens at various arginine levels. No diet effect was observed. Mitogenesis was maximal when media arginine approximated normal plasma levels. Our results suggest that supplemental arginine has little effect on lymphocyte proliferation or IL-2 production in healthy young and aged rats.