Differential impact of L-arginine deprivation on the activation and effector functions of T cells and macrophages

The metabolism of the amino acid L-arginine is emerging as a crucial mechanism for the regulation of immune responses. Here, we characterized the impact of L-arginine deprivation on T cell and macrophage (M Phi) effector functions: We show that whereas L-arginine is required unconditionally for T cell activation, M Phi can up-regulate activation markers and produce cytokines and chemokines in the absence of L-arginine. Furthermore, we show that L-arginine deprivation does not affect the capacity of activated M Phi to up-regulate L-arginine-metabolizing enzymes such as inducible NO synthase and arginase 1. Thus, our results show that to exert their effector functions, T cells and M Phi have different requirements for L-arginine. J. Leukoc. Biol. 85: 268-277; 2009.