TLR4 and Sepsis: During sepsis, we observed up-regulation of surface receptors, including Toll-like receptor 4 (Tlr4), Interleukin-4 receptor alpha (Il4ra), Interleukin-13 receptor alpha-1 (Il13ra1), and interferon-stimulated genes (IFITM family members including Ifitm6, Ifitm3, Ifitm2, Ifitm1, and Ifit1), implying the involvement of LPS (Tlr4 ligand), IL-4, IL-13, and interferon (IFN) in the immunomodulatory activities of this MDSC subset in septic hosts (Figure 7B).