Effects Of Lactobacillus Casei On Differentiation Of Treg And Th17 Cells In The Mouse Of Enterotoxigenic Escherichia Coli K88-induced Enteritis Model

Piglet diarrhea is the common infectious disease which is caused by Escherichia coli(ETEC) K88.The disease with high morbidity and mortality, is the threat for the development of pigs breeding industry. Lactic acid bacteria can regulate immune response, promote T cell development, and induce various cytokine production resulting in the inhibition of the inflammation reaction. To study the mechanism of lactic acid bacteria in preventing the infection of Escherichia coli, this reaserch established the model of bacterial enteritis of BALB/c mice induced by ETEC K88.The mice were continuously irrigated with ETEC K88 bacteria liquid at concentrations of 1.0×107CFU/mL, 1.0×108CFU/mL and 1.0×109CFU/mL for 3 days,respectively. The main cytokines in peripheral blood were detected and the pathological sections of duodenum were observed to determine whether the model of bacterial enteritis succeded or not. Thereafter, L.casei ATCC393 strain was used to intervene in the mice with enteritis. Then we used ELISA to detect the changes of IL-10, IL-17, IL-6 and TGF-β in peripheral blood, and flow cytometry to analyze the number of CD4+CD25+Foxp3+Tregsand CD4+IL-17a+Th17 in spleen and mesenteric lymph nodes of spenocytes. Weston blot and qPCR were also adopted to analyze mRNA level and protein expression levels of Foxp3 and RORγt in mesenteric lymph node.The results showed that after gavage of Escherichia coli, the appetite and body weight of mice were both decrease, the contents of MPO, TNF-α and IL-1β in peripheral blood were increase, and the inflammatory reactions were observed through the histopathologic slides of duodenum. Eight days after perfusion, the feces of mice became soft, the body weight declined to the lowest, and the content of cytokines in model group reached the peak which was significarctly different from that in the control group(p<0.05). Besides, the gap between mucosa and muscular became wide, the number of goblet cells was increased, and inflammatory cells infiltrated between lamina propria and mucosa. There was the most obvious change in inflammatory. Therefore, the different concentration of bacteria had little effect on the levels of inflammatory cytokines(p>0.05).Continuously irrigating with L.caselto intervene mice with enteritis for 7 days, the inflammation symptoms were alleviated.There was increase in the contents of IL-10 and TGF-β and decrease in IL-6 andIL-17, which was significantly differenent from that of enteritis group(P<0.05).The number of Tregs in spleen and mesenteric lymph nodes grew and the number of Th17 cells was reduced. The mRNA level and protein expression level of specific transcription factor Foxp3 and RORγt rose, which had significant difference with that of enteritis group(P<0.05). In summary, irrigation with L.casel had preventive effects on mice infected by Escherichia coli via through promoting the differention of T cells to Tregs, inhibiting the differentiation of Th17 cells and releasing inflammation-related cytokines. This study provides a theoretical basis for the prevention and control of animal colibacillosis.