Transforming growth factor-beta1 and splenocyte apoptotic cell death after burn injuries

Transforming growth factor (TGF)-beta1 is a multifunctional cytokine that mediates apoptotic cell death in human lymphocytes in vitro. To better understand the mechanism through which TGF-beta1 exerts its apoptotic effect, we investigated the role of TGF-beta1 in the relationship between burn injury and cell death of splenocytes in a mouse model of either 0%, 25%, or 40% full-thickness burns. Mice were killed and spleens were harvested at 15 and 30 minutes and at 1, 2, 4, 8, 12, and 24 hours after the burn. The spleens were divided and used for both histologic analyses with H-E stain and TUNEL stain and for total messenger RNA isolation and reverse transcriptase-polymerase chain reaction amplification. Amplified polymerase chain reaction products were analyzed for signal strength by electrophoresis. TGF-beta1 RNA expression was highest at 2 hours after the burn injuries in the 40% full-thickness burns and at 4 hours after the burn injuries in the 25% full-thickness burns. The relative increase in TGF-beta1 RNA was 3 times greater with the larger burn than with the smaller burn. In histologic analysis, splenocyte apoptotic cell death was observed at 4 to 24 hours after the burn in the 40% full-thickness burns but at only 4 to 12 hours in the 25% full-thickness burns. TGF-beta1 RNA peak expression was observed at different times after the burn in 25% and 40% full-thickness burns. Histologic analysis showed apoptotic cell death in proportion with respective messenger RNA expressions. This suggests that TGF-beta1 may be associated with apoptosis of splenocytes in vivo and that the effect of TGF-beta1 after a burn injury may be important in the immune system.