EFFECTS OF THE STRESS-RESPONSE IN SEPTIC RATS AND LPS-STIMULATED ALVEOLAR MACROPHAGES - EVIDENCE FOR TNF-ALPHA POSTTRANSLATIONAL REGULATION

We have previously demonstrated that induction of the stress response, by heat stress or sodium arsenite, administered 18 h before initiatio n 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 (l ipopolysaccharide, LPS) stimulation, would cause a decrease in synthes is and/or release of tumor necrosis factor-alpha (TNF-alpha), making t he animals more resistant to sepsis. Rats exposed to Salmonella typhos a LPS demonstrated a rise in plasma TNF-alpha. In contrast, rats expos ed to heat stress or to sodium arsenite 18 h prior to LPS had signific antly lower levels of plasma TNF-alpha. To examine the mechanisms by w hich the stress response mediates this decrease, we studied cultured a lveolar macrophages. Similar to in vivo studies, TNF released into sup ernatants of alveolar macrophages treated with LPS was significantly h igher than from cells exposed to the stress response prior to LPS. The decrease in TNF-alpha protein release was not accompanied by a simila r decrease in TNF-alpha mRNA levels or by a decrease in cell-associate d TNF-alpha, suggesting possible posttranslational regulation of TNF-a lpha. To determine whether the decrease in TNF-alpha release was due t o binding and sequestration by heat shock proteins (HSP), TNF-alpha wa s purified by immunoprecipitation. Under these conditions, TNF-alpha a nd HSP72kDa coprecipitated from cells that had received stress treatme nt prior to LPS. These data implicate HSP in posttranslational control of TNF-alpha release in LPS-stimulated alveolar macrophages exposed t o the stress response.