Burn-induced gut mucosal homeostasis in TCR delta receptor-deficient mice

Gammadelta T lymphocytes make up approximately 50% of lymphocytes in the intestine. These cells have been shown to prime macrophages for TNF-alpha production after burn. We previously showed that neutralizing anti-TNF-alpha antibodies reduce mucosal atrophy by decreasing gut epithelial apoptosis after severe burn. We hypothesized that burn-induced mucosal turnover is diminished in T cell receptor delta gene knockout (TCR delta-/-) mice through diminished TNF-alpha activity. Forty-two wild-type and 42 TCR delta-/- mice (C57-BL6) were randomly assigned to burn and sham burn groups. The burn group underwent a 25% total body surface area (TBSA) scald burn. The proximal small intestine was harvested at 2, 12, and 48 h. To assess mucosal atrophy, mucosal height and cell numbers in the villi and crypts were determined on hematoxylin and eosin-stained tissue sections. Apoptotic gut epithelium was identified by terminal deoxyuridine nick-end labeling (TUNEL) staining, and cell proliferation was detected by immunostaining for proliferative cell nuclear antigen (PCNA). TNF-alpha mRNA expression was measured by RT-PCR. Caspase-8 activity was measured by colorimetric assay. Statistical analysis was performed with two-way analysis of variance and t testing. Significance was accepted at P < 0.05. Data are expressed as means +/- SEM. TNF-alpha mRNA expression was significantly decreased in TCR delta-/- mice at 2 h after burn. Gut epithelial apoptosis and proliferation in both wild-type and TCR delta-/- mice were significantly increased after burn, but TCR delta-/- mice had a significantly lower levels of apoptosis (P < 0.01) and proliferation (P < 0.05) when compared with wild-type mice. Burn-induced mucosal atrophy was identified in groups by decreasing villus height, crypt depth, and villus and crypt cell number (P < 0.001) compared with sham, but no difference was found between wild-type and TCR delta-/- mice. Caspase-8 activity was significantly diminished in TCR delta-/- mice compared with wild-type mice. Gammadelta T cells are associated with increased TNF-alpha expression and gut epithelial turnover in the small bowel after severe burn. However, absence of delta T cell receptor did not inhibit mucosal atrophy after severe burn. This study suggests that gut mucosal atrophy after severe burn is a multifactorial process associated with increased TNF-alpha activity.