Gram-negative bacteria including Escherichia coli, Citrobacter rodentium, Salmonella typhimurium, and Shigella flexneri are sensed in an ill-defined manner by an intracellular inflammasome complex that activates caspase-11. We show that macrophages loaded with synthetic lipid A, E. coli lipopolysaccharide (LPS), or S. typhimurium LPS activate caspase-11 independently of the LPS receptor Toll-like receptor 4 (TLR4). Consistent with lipid A triggering the noncanonical inflammasome, LPS containing a divergent lipid A structure antagonized caspase-11 activation in response to E. coli LPS or Gram-negative bacteria. Moreover, LPS-mutant E. coli failed to activate caspase-11. Tlr4(-/-) mice primed with TLR3 agonist polyinosinic:polycytidylic acid [poly(I:C)] to induce pro-caspase-11 expression were as susceptible as wild-type mice were to sepsis induced by E. coli LPS. These data unveil a TLR4-independent mechanism for innate immune recognition of LPS.

A large number of macrophages and haematopoietic progenitor cells accumulate in pre-metastatic lungs in which chemoattractants, such as S100A8 and S100A9, are produced by distant primary tumours serving as metastatic soil. The exact mechanism by which these chemoattractants elicit cell accumulation is not known. Here, we show that serum amyloid A (SAA) 3, which is induced in pre-metastatic lungs by S100A8 and S100A9, has a role in the accumulation of myeloid cells and acts as a positive-feedback regulator for chemoattractant secretion. We also show that in lung endothelial cells and macrophages, Toll-like receptor (TLR) 4 acts as a functional receptor for SAA3 in the pre-metastatic phase. In our study, SAA3 stimulated NF-kappaB signalling in a TLR4-dependent manner and facilitated metastasis. This inflammation-like state accelerated the migration of primary tumour cells to lung tissues, but this was suppressed by the inhibition of either TLR4 or SAA3. Thus, blocking SAA3-TLR4 function in the pre-metastatic phase could prove to be an effective strategy for the prevention of pulmonary metastasis.

No abstract

Although coagulation factors play a role in host defense for “living fossils” such as horseshoe crabs, the role of the coagulation system in immunity in higher organisms remains unclear. We modeled the interface of human species C adenovirus (HAdv) interaction with coagulation factor X (FX) and introduced a mutation that abrogated formation of the HAdv-FX complex. In vivo genome-wide transcriptional profiling revealed that FX-binding–ablated virus failed to activate a distinct network of nuclear factor κB–dependent early-response genes that are activated by HAdv-FX complex downstream of TLR4/MyD88/TRIF/TRAF6 signaling. Our study implicates host factor “decoration” of the virus as a mechanism to trigger an innate immune sensor that responds to a misplacement of coagulation FX from the blood into intracellular macrophage compartments upon virus entry into the cell.