Analysis by radio-HPLC of the conversion of L-[³H]arginine into L-[³H]citrulline and [³H]ornithine by GVHR spleen cells (either untreated or treated by Con A or LPS). The effects of LMMA (1.5 mmol/L), neutralizing anti–IFN-γ MoAb (1.5 μg/mL), and LME treatment on the production of L-arginine–derived metabolites is also presented (see Materials and Methods for details of experimental procedures). In parallel with HPLC analyses, the GVHR-associated immunosuppression was tested: (+) indicates that suppression was observed, (−) that it was not.