Reduction of intestinal mucosal immune function in heat-stressed rats and bacterial translocation

Purpose: The aim of this study was to further understand the effects and mechanism of heat stress on the intestinal mucosal immune system of the rat, including changes in the intestinal mucosal barrier and immune function and their effects on bacterial translocation. Materials and methods: Sprague Dawley (SD) rats were randomly divided into control and heat-stress groups. Both groups were housed in a 25 degrees C environment of 60% relative humidity. The heat-stress group was subjected to 40 degrees C for 2 h daily over 3 days. Results: Compared with the control group villi length in the small intestines of the heat-stress group was shortened. Jejunal mucosa were seriously damaged and the number of goblet cells in the epithelia of the duodenum and jejunum was significantly reduced. Electron microscopy revealed intestinal mucosal disorder, a large number of exudates of inflammatory fibrous material, fuzzy tight junction structure between epithelial cells, and cell gap increases in the heat-stress group. Transcription of IFN-gamma, IL-2, IL-4, and IL-10, was significantly reduced, as was that of the intestinal mucosal immune-related proteins TLR2, TLR4, and IgA. The number of CD3(+) T cells and CD3(+)CD4(+)CD8(-) T cells in the mesenteric lymph nodes (MLNs) was significantly lower, while the number of CD3(+)CD4(-)CD8(+) T cells was significantly increased. The bacteria isolated from the MLNs were Escherichia coli. Conclusions: Heat stress damages rat intestinal mechanical and mucosal immune barriers, and reduces immune function of the intestinal mucosa and mesenteric lymphoid tissues, leading to bacterial translocation.