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 (MΦ) effector functions: We show that whereas l ‐arginine is required unconditionally for T cell activation, MΦ 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 MΦ 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 MΦ have different requirements for l ‐arginine.