Induction of interferon by bacterial endotoxin

The role of autophagy in Crohn's disease

(Macro)-autophagy is a homeostatic process by which eukaryotic cells dispose of protein aggregates and damaged organelles. Autophagy is also used to degrade micro-organisms that invade intracellularly in a process termed xenophagy. Genome-wide association scans have recently identified autophagy genes as conferring susceptibility to Crohn’s disease (CD), one of the chronic inflammatory bowel diseases, with evidence suggesting that CD arises from a defective innate immune response to enteric bacteria. Here we review the emerging role of autophagy in CD, with particular focus on xenophagy and enteric E. coli strains with an adherent and invasive phenotype that have been consistently isolated from CD patients with ileal disease.

Analysis of endotoxin fever in rabbits by using a monoclonal antibody to tumor necrosis factor (cachectin)

A murine monoclonal antibody to rabbit tumor necrosis factor (TNF; cachectin) was injected intravenously into an endotoxin-treated rabbit to examine the role of endogenous TNF in fever. Both early and late peaks of biphasic fever evoked by the endotoxin injection were suppressed by the antibody. TNF activity was detected in an endotoxin dose-dependent manner in the blood 1 h after the endotoxin injection, which was coincident with the early-peak fever. Although the late-peak fever responded to the antibody, no significant TNF activity was detected in the blood obtained 1 h before the peak response. The blood was found to contain endogenous pyrogen activity, which was stable after heating at 70 degrees C for 30 min and resistant to in vitro treatment with the antibody. Rabbit TNF injection also elicited biphasic fever in rabbits, the second phase of which was found to be mediated by the similar endogenous pyrogen. These results suggest that endogenous TNF plays an important role in eliciting a febrile response to endotoxin.

Natural and recombinant interferons inhibit epithelial cell invasion by Shigella spp

The effect of natural and recombinant interferons (IFNs) on the abilities of Shigella flexneri, S. sonnei, and Salmonella typhimurium to invade different human and murine cells was examined. Pretreatment of cell monolayers with natural and recombinant IFNs reduced the number of Shigella-infected cells in a dose-dependent manner. Establishment of an anti-invasive cellular state was time dependent, requiring 10 h for 50% inhibition of bacterial invasion. The inhibitory effect of IFN was species specific, with human or murine IFN effective against homologous but not heterologous cells. Gamma IFN was slightly more potent than alpha IFN at inhibiting bacterial invasion. Inhibition of Shigella invasion was dependent on the challenge dose of bacteria. Little inhibition of invasion was seen when cells were pretreated with low concentrations of IFN and challenged with high multiplicities of infection of Shigella sp. In contrast to Shigella invasion, the maximum inhibitory effect of IFN on Salmonella invasion of cells was observed at low levels (5 to 50 U) of IFN. These results suggest that Shigella and Salmonella invasions occur at unique sites on eucaryotic cells or by different penetration mechanisms. More importantly, these data suggest that IFN may play a significant role in host defense against Shigella and Salmonella infections.