Arginase 1 and IDO are not M-MDSC mechanisms of immunosuppression in DLBCL. (A) Expression of ARG1, IDO1, NOS2, HO-1, and PTGS2 was evaluated by TLDA on 17 DLBCL and 15 HD samples. The relative gene expression (mRNA) of PBMCs from DLBCL and HD was compared (ratio of the mean expression on DLBCL to the mean expression on HD). (B) Arginase 1 and IDO activities were evaluated by high-performance liquid chromatography with the ratio ornithine to arginine and kynurenine to tryptophan, respectively (n = 31 DLBCL and 21 HD). (C) Arginase 1 in plasma was evaluated by ELISA (n = 43 DLBCL and 33 HD). *P < .05, **P < .01, ***P < .001. (D) Percentage of increase or decrease in T-cell proliferation (proliferation index) between treated (L-1MT or nor-NOHA) and untreated cells, evaluated for CD4^pos and CD8^pos cells by CFSE labeling (n = 8 DLBCL for L-1MT and n = 7 for nor-NOHA). DLBCL patients were classified into groups: without (Gr.1, n = 5) or with (Gr.2, n = 2 or 3) suppressive monocytes. The classification was based on suppressive assay or a number of M-MDSCs at more than threefold the median count. (E) Correlation of the arginase 1 in plasma and M-MDSC count (left) or immature granulocytes count (Imm gran) (right) count in DLBCL peripheral blood (n = 36 DLBCL). ns, not significant.