TLR4 and neoplasm: It has been reported that TLR2 and TLR4 agonists can directly induce the production of IL-6 and other cytokines in myeloid cells.25 Shen et al. demonstrated that tumor-derived exosomes induce DCs to produce IL-6 in a TLR2- and TLR4-dependent manner.42 In addition, tumor-derived exosomes have been reported to trigger Stat3 activation in MDSCs to induce IL-6 secretion via the TLR2/MyD88 pathway.40 Here, we found significantly decreased IL-6 production in MDSCs upon blocking the TLR4 pathway, indicating that the endogenous production of IL-6 by MDSCs is mainly dependent upon the TLR4 pathway.