Correction to: IL-1b is a key cytokine that induces trypsin upregulation in the influenza virus-cytokine-trypsin cycle.

The original article can be found online.

IL-1ß is a key cytokine that induces trypsin upregulation in the influenza virus-cytokine-trypsin cycle.

Severe influenza is characterized by a cytokine storm, and the influenza virus-cytokine-trypsin cycle is one of the important mechanisms of viral multiplication and multiple organ failure. The aim of this study was to define the key cytokine(s) responsible for trypsin upregulation. Mice were infected with influenza virus strain A/Puerto Rico/8/34 (H1N1) or treated individually or with a combination of interleukin-1ß, interleukin-6, and tumor necrosis factor α. The levels of these cytokines and trypsin in the lungs were monitored. The neutralizing effects of anti-IL-1ß antibodies on cytokine and trypsin expression in human A549 cells and lung inflammation in the infected mice were examined. Infection induced interleukin-1ß, interleukin-6, tumor necrosis factor α, and ectopic trypsin in mouse lungs in a dose- and time-dependent manner. Intraperitoneal administration of interleukin-1ß combined with other cytokines tended to upregulate trypsin and cytokine expression in the lungs, but the combination without interleukin-1ß did not induce trypsin. In contrast, incubation of A549 cells with interleukin-1ß alone induced both cytokines and trypsin, and anti-interleukin-1ß antibody treatment abrogated these effects. Administration of the antibody in the infected mice reduced lung inflammation area. These findings suggest that IL-1ß plays a key role in trypsin upregulation and has a pathological role in multiple organ failure.

Influenza A virus infection of vascular endothelial cells induces GSK-3ß-mediated ß-catenin degradation in adherens junctions, with a resultant increase in membrane permeability.

Multiorgan failure with vascular hyperpermeability is the final outcome in the progression of seasonal influenza virus pneumonia and influenza-associated encephalopathy, and it is also common in infection with highly pathogenic avian influenza virus. However, the precise molecular mechanism by which influenza virus infection causes vascular endothelial cell hyperpermeability remains poorly defined. We investigated the mechanisms of hyperpermeability of human umbilical vein endothelial cells infected with influenza A virus (IAV)/Puerto Rico/8/34 (PR8) (H1N1). The levels of ß-catenin, a key regulatory component of the vascular endothelial-cadherin cell adhesion complex, were markedly decreased during infection for 28 h, with increments of vascular hyperpermeability measured by transendothelial electrical resistance. Lactacystin (at 2 µM), a proteasome inhibitor, inhibited the decrease in ß-catenin levels. Since the N-terminal phosphorylation of ß-catenin by glycogen synthase kinase (GSK)-3ß is the initiation step of proteasome-dependent degradation, we examined the effects of GSK-3ß suppression by RNA interference in endothelial cells. IAV-infection-induced ß-catenin degradation was significantly inhibited in GSK-3ß-knockdown cells, and transfection of cells with recombinant ß-catenin significantly suppressed IAV-induced hyperpermeability. These findings suggest that IAV infection induces GSK-3ß-mediated ß-catenin degradation in the adherens junctional complexes and induces vascular hyperpermeability. The in vitro findings of ß-catenin degradation and activation of GSK-3ß after IAV infection were confirmed in lungs of mice infected with IAV PR8 during the course of infection from day 0 to day 6. These results suggest that GSK-3ß-mediated ß-catenin degradation in adherens junctions is one of the key mechanisms of vascular hyperpermeability in severe influenza.