ALTERED GENE-TRANSCRIPTION AFTER BURN INJURY RESULTS IN DEPRESSED T-LYMPHOCYTE ACTIVATION

Objective Patients with major burns and an animal model of burn injury were studied to determine the mechanism of depressed interleukin-2 (I L-2) production after thermal injury and to determine the effect of su ch injury on IL-2 receptor (IL-2R) expression and function. Summary Ba ckground Data Major burn injury is known to diminish resistance to inf ection by altering cytokine production and prostanoic secretion and by inhibiting T-lymphocyte activation. T-cell activation requires produc tion of regulatory cytokines, principally IL-2, and expression of the appropriate cytokine receptors, Depressed IL-2 production after major burn injury is undisputed, although the molecular mechanisms remain un defined; the effect of burn injury on IL-2R expression and function cu rrently is controversial. Methods The authors studied serial samples o f peripheral blood mononuclear cells (PBMC) from 11 patients with 25% to 95% surface area burns and 7 age-matched volunteer control subjects . Peripheral blood mononuclear cells were stimulated by the T-cell mit ogen phytohemagglutinin (PHA), and IL-2 production and mRNA expression by Northern blot were determined. Expression and function of IL-2R we re determined by monoclonal antibodies to the p55 and p75 chains of th e IL-2R, binding of fluorescein-labeled IL-2, and response to exogenou s recombinant IL-2. We also studied a mouse model of 20% burn injury k nown to mimic the immune abnormalities seen in humans with burns. Sple nocytes from mice with burns (20-22 per group) were studied for IL-2 p roduction and IL-2 mRNA expression after stimulation with the T-cell m itogen concanavalin A (ConA) and compared with sham burn control subje cts. Kinetics of mRNA expression after ConA stimulation also were dete rmined and a nuclear run-on assay performed to determine IL-2 gene tra nscription. The mRNA expression was determined for the proto-oncogenes c-jun and c-fos, whose protein products join to form transcription fa ctor AP1, which is necessary for activation of the IL-2 promoter. Sple nocytes from mice with burns after ConA stimulation also were studied for expression and function of the IL-2R. Results Peripheral blood mon onuclear cells from burn patients compared with healthy control subjec ts showed diminished (p < 0.05) IL-2 production and mRNA expression 4 to 10 days after burn injury. Burn PBMC demonstrated normal expression of IL-2R, p55, and p75 chains 0 to 7, 8 to 20, and 21 to 37 days afte r burn injury, normal IL-2R binding of fluorescein-labeled IL-2, and a normal proliferative response to PHA in the presence of exogenous rec ombinant IL-1. Splenocytes from mice 7 days after burn injury shaved d iminished production (p < 0.05) of IL-2 and IL-2 mRNA expression after ConA stimulation as compared with sham burn control subjects, Kinetic s of mRNA expression after ConA stimulation were the same for burn and control mice, indicating that reduced IL-2 mRNA expression was not ca used by altered mRNA degradation. A nuclear run-on assay confirmed dec reased 11-2 gene transcription in burn splenocytes. Burn splenocytes s howed normal expression of mRNA for c-jun but diminished expression of mRNA for c-fos. Finally, splenocytes from mice with burns after ConA stimulation showed normal expression and function of the IL-2R 7, 10, 14, and 21 days after burn injury. Conclusions These human and animal studies indicate that major burn injury depresses T-cell activation at the level of IL-2 gene transcription at least in part by inhibiting c -ros expression, whereas IL-2R expression and function remain normal a nd T-cell proliferation can be restored to normal levels by exogenous IL-2,