Figure 4.

Stimulated T cells convert citrulline to arginine only when cultured in the presence of 20 µM arginine, but not in its complete absence. Primary human CD3⁺ T lymphocytes were isolated from blood of healthy donors by negative selection and stimulated in the presence of 20 µM arginine or in the complete absence of arginine with anti-CD3/anti-CD28-tagged beads for 96 h. Citrulline at a final concentration of 1 mM was then added to the cells and they were either incubated for further 1 or 4 h or citrulline was removed immediately (t = 0 h). Intracellular concentrations of (A) citrulline, (B) argininosuccinate, and (C) arginine were quantified by high performance liquid chromatography. Statistical calculations were performed with two-way analysis of variance (n = 3).