In order to perform their functions, macrophages must be activated either by Th1-type cytokines, such as interferon-gamma which is called classical activation or M1, or by Th2-type cytokines, such as IL-4, IL-10, IL-13, etc. referred as alternative activation or M2. In all of these conditions, macrophages require the uptake of exogenous arginine to meet their metabolic demands. Depending on the intracellular availability of this amino acid, the activities of these cells are differentially modulated. In this regard, macrophage activation requires this amino acid for the synthesis of proteins, production of nitric oxide via classical activation, and production of polyamines and proline through alternative activation. Therefore, the study of the arginine transport for amino acid system transporters may be a key regulatory step for physiological responses in macrophages. In this chapter, we present simple and direct methods to determine the mRNA expression and activity of arginine transporters. Moreover, we describe a direct method to measure the arginine catabolism using thin-layer chromatography.
