To gain insight into the role of different immune cell populations in the natural history of metastatic NB, we have evaluated the mRNA expression of the following molecular markers in 41 primary tumors at diagnosis: CD45: all leukocytes, CD14: monocyte-macrophages, ARG1: activated macrophages, CD163: M2 TAM, CD4: T helper cells, FOXP3: Treg, Perforin-1 (PRF1), and Granzyme B (GRMB): cytotoxic T lymphocytes and activated NK cells. This evidence concerns the gene ARG1 and neuroblastoma.