Although mIL-21 may be acting directly on mouse neutrophils causing them to phagocytose opsonized tumor cells, enhance ADCC, or produce cytotoxic oxygen intermediates, a direct effect of IL-21 on neutrophils is not supported by studies with human neutrophils where IL-21R was not detected and human IL-21 did not modulate neutrophil responses including superoxide production, phagocytosis, chemotaxis and cytokine production [34]. This evidence concerns the gene IL21R and neoplasm.