In order to better understand the functional relevance of CD11b+ cells infiltrating glioma and the influence of CXCR4 inhibition on the functional phenotype of these cells, we analyzed the expression of inducible nitric oxide synthase (iNOS), an enzyme typically involved in microglia/macrophage pro-inflammatory activity (M1 phenotype), and arginase-1 (Arg-1), as a marker of immunosuppressive activity (M2 phenotype). The gene discussed is ARG1; the disease is central nervous system cancer.