Mechanism of increased tumor necrosis factor production after thermal injury. Altered sensitivity to PGE2 and immunomodulation with indomethacin.

Altered macrophage function after thermal injury is associated with increased production of PGE2 and TNF. However, it is not clear why synthesis of both cellular products remains elevated, as PGE2 is a potent inhibitor of TNF secretion. We studied the relationship between PGE2 and TNF synthesis in a murine model of thermal injury, and examined the effect of prostaglandin blockade on splenic macrophage secretion of these mediators of inflammation. LPS-stimulated production of PGE2 was significantly elevated in burn groups compared with sham-burned controls (pg/ml mean(SEM); sham 151(32): burn 597(147), p < 0.01). TNF production was similarly increased after thermal injury (pg/ml mean(SEM); sham 62(20): burn 928(316), p < 0.01). In vitro culture of macrophages with indomethacin augmented LPS stimulated TNF production in sham-burned controls but did not affect synthesis in burn groups, suggesting a loss of PGE2-dependent regulation of TNF synthesis after thermal injury. Direct measurement of TNF secretion as a function of exogenous PGE2 confirmed this dissociation between PGE2 and TNF synthesis, as burned animals displayed a 5-fold reduction in sensitivity to PGE2-induced inhibition of TNF, when compared with sham-burned controls (ID50 PGE2 molar; sham 1.26 x 10(-8): burn 6.43 x 10(-8), p < 0.05). In vivo pretreatment of burn groups with indomethacin for 5 days before assay partially restored sensitivity to the prostaglandin, and significantly down-regulated synthesis of both TNF and PGE2. These data show that thermal injury is associated with a loss of PGE2-dependent down-regulation of TNF synthesis, which accounts at least in part for increased TNF in these animals. In vivo cyclooxygenase blockade partially restored sensitivity to the prostaglandin and consequently down-regulated synthesis of TNF. These data further support existing evidence that suggests a potential therapeutic role for cyclooxygenase blockade after major thermal injury and trauma.