IL6 trans-signaling promotes functional recovery of hypofunctional phagocytes through STAT3 activation during peritonitis.

OBJECTIVE: The role of high interleukin 6 (IL6) levels has not been clearly explained in severe sepsis. We show that the augmentation of the IL6 signal by recombinant IL6 receptors (rIL6R) delivery allows the functional recovery of phagocytes in a peritonitis mouse model. MATERIALS AND METHODS: Mice were challenged intraperitoneally (i.p.) with live Staphylococcus aureus for effect of IL6R delivery on the 24 h-survival, bacterial clearance and cellular responses. In additional experiments to assess the effect of IL6R delivery on phagocytosis, the model was i.p. inoculated with heat-killed S. aureus with or without rIL6R and the peritoneal lavage fluid and cells were collected at 1 h after the i.p. inoculation of S. aureus. RESULTS: The IL6R delivery tended to improve 24 h survival and increase bacteria clearance from the septic mice. The rIL6R treatment to heat-killed bacteria challenged mice augmented the uptake of bacteria and phagosome acidification, inducing the phosphorylation of STAT3 in peritoneal cells within 1 h after the IL6R delivery. Furthermore, the rIL6R delivery prevented the extracellular release of neutrophil elastase activity and myeloperoxidase (harmful factors). CONCLUSIONS: These results indicate that augmentation of IL6 signaling appears to be critical for the effective management of hypofunctional neutrophils during severe inflammation, such as sepsis.

Local delivery of soluble interleukin-6 receptors to improve the outcome of alpha-toxin producing Staphylococcus aureus infection in mice.

Staphylococcal alpha-toxin enhances interleukin (IL)-6 secretion in mice infected with Staphylococcus aureus. The role of alpha-toxin-induced IL-6 secretion in host defense has not been sufficiently clarified. In the present study, IL-6 signaling was transiently regulated using soluble IL-6 receptors (sIL-6R) to investigate the role of IL-6 in the early stage of abdominal S. aureus infection. In mice challenged with bacteria producing high alpha-toxin levels, the local delivery of sIL-6R was effective in improving the survival rate, the resolution of neutrophilia and the bacteria clearance. Mice that had received sIL-6R and survived showed high levels of IL-6, monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha. In contrast, mice that died in spite of the delivery of sIL-6R showed high levels of interferon (IFN)-gamma and IL-1alpha and low TNF-alpha level. When the effect of soluble gp130, a sIL-6R antagonist, was examined, the number of neutrophils increased significantly and the MCP-1 level decreased significantly, compared to the group that received sIL-6R alone; the number of viable bacteria also tended to increase as a result of the inhibition of IL-6 signaling. The cellular phosphotyrosine level in alpha-toxin-treated macrophages was reduced in cultures supplemented with recombinant IL-6 in vitro. These results suggest that IL-6 enhances bactericidal activity and reduces the number of immune cells that are activated abnormally through the regulation of inflammatory cytokines during the early stage of infection in alpha-toxin producers.

Staphylococcal alpha-toxin synergistically enhances inflammation caused by bacterial components.

This study was performed to investigate the in vivo effects of staphylococcal alpha-toxin on phagocytosis and the secretion of proinflammatory cytokines at local sites of intraperitoneal toxin-challenged mice. A dosage of 45 hemolytic units (HU) of alpha-toxin induced a marked increase in the peritoneal neutrophil count. The toxin caused a 52% decrease in phagocytosis by peritoneal macrophages, compared with that of control mice receiving Staphylococcus aureus particles alone. However, no effect on phagocytosis in neutrophils was observed. A dosage of 45 HU toxin and the synergistic activity of S. aureus particles strongly induced interleukin (IL) 6 secretion but only mildly induced IL-1alpha secretion. The toxin did not induce the secretion of tumor necrosis factor-alpha (TNF-alpha). Interestingly, S. aureus culture supernatant induced the secretion of TNF-alpha in cultured macrophages. These results suggest that alpha-toxin damages the primary host defense system by inducing the oversecretion of IL-1alpha and IL-6, but not TNF-alpha, via a mechanism that requires the synergistic action of bacterial components.