IL6 and neuroblastoma: Based upon the release of TGFβ1 by tumor cells and of IL-6 and TGFβ1 by monocytes cultured in tumor cell CM and upon the possibility that these cytokines could suppress activation of NK cells [5, 7], we determined the effect of neuroblastoma/monocyte co-culture CM on IL-2 activation of purified NK cells using cytotoxicity and IFNγ secretion as end points (Fig. 2c–e).