Further support of the hypothesis that interaction of E5564 at CD14 does not play a key role in its activity comes from a previous study by Lien et al. describing the activity of novel synthetic acyclic lipid A-like agonists that activate TLR4/MD-2 in the absence of CD14 (62) . E5564 inhibited the actions of these agonists under serum-free conditions. Taken together, these lines of evidence make it tempting to speculate that E5564 binds to TLR4/MD-2 complex, thereby blocking LPS binding or transmembrane signaling. The downstream effect of inhibiting the initial signaling by LPS seems to be an inhibition of all LPS-induced cytokines measured, including TNF-, IL-1, IL-6, IL-8, IL-10, and nitric oxide, which was measured in cultured cells, whole blood, and in vivo. Recently the crystal structure of the TLR4/MD-2 and E5564 has been described confirming the physical interaction of these molecules (57) .