TLR4 and plasma cell myeloma: Additionally, the production of S100A9, a calcium-binding protein that stimulates the secretion of TNF-α, IL-6, and IL-10 through toll-like receptor 4(TLR4)-mediated autocrine signaling, by MDSCs in the tumor microenvironment (TME) attracts myeloma cells (91) and fosters their growth by activating the canonical nuclear factor-kappa B(NF-κB) pathway (92).