ARG1 and neoplasm: Treatment of either CD33+ or CD11b+ tumor-cell line-induced MDSC with lipopolysaccharide, a known activator of MDSC function [39], caused further up-regulation of STAT3, C/EBPβ, and HIF1α concurrent with increased expression of ARG-1, iNOS, and NOX2-component NCF1 (data not shown).