We have previously demonstrated that induction of the stress response, by heat stress or
sodium arsenite, administered 18 h before initiation of
sepsis in rats, significantly decreased mortality and
lung injury. As a possible mechanism underlying this effect, we hypothesized that the induction of the stress response, prior to bacterial
endotoxin (
lipopolysaccharide, LPS) stimulation, would cause a decrease in synthesis and/or release of
tumor necrosis factor-alpha (
TNF-alpha), making the animals more resistant to
sepsis. Rats exposed to Salmonella typhosa LPS demonstrated a rise in plasma
TNF-alpha. In contrast, rats exposed to heat stress or to
sodium arsenite 18 h prior to LPS had significantly lower levels of plasma
TNF-alpha. To examine the mechanisms by which the stress response mediates this decrease, we studied cultured alveolar macrophages. Similar to in vivo studies, TNF released into supernatants of alveolar macrophages treated with LPS was significantly higher than from cells exposed to the stress response prior to LPS. The decrease in
TNF-alpha protein release was not accompanied by a similar decrease in
TNF-alpha mRNA levels or by a decrease in cell-associated
TNF-alpha, suggesting possible posttranslational regulation of
TNF-alpha. To determine whether the decrease in
TNF-alpha release was due to binding and sequestration by
heat shock proteins (HSP),
TNF-alpha was purified by immunoprecipitation. Under these conditions,
TNF-alpha and HSP72kDa coprecipitated from cells that had received stress treatment prior to LPS. These data implicate HSP in posttranslational control of
TNF-alpha release in LPS-stimulated alveolar macrophages exposed to the stress response.