Regulation of CD4+CD8–CD25+ and CD4+CD8+CD25+ T cells by gut microbiota in chicken

Abstract

Gut microbiota in chicken has long been studied and considered for mostly growth performance point of view. And therefore, immunological studies regarding gut homeostasis in chicken have been insufficiently achieved. Regulatory T cells (Tregs) are a notable subtype of CD4+ T cells playing an important role to maintain gut homeostasis in humans and animals. Intestinal Tregs are induced by gut microbiota, such as, Clostridium spp. cluster IV and XIVa strains, altered Schaedler flora (ASF), or Bacteroides fragilis in mice. Although it has been suggested that CD4+CD25+ T cells act as Tregs, there are no such studies showing the relationship between gut microbiota and Tregs in chickens. The first, I established the model for ABX-treated chickens by the administration of various concentrations of antibiotic cocktail consisting of ampicillin, gentamycin, neomycin, metronidazole, and vancomycin in water. Cecal contents from chickens treated with antibiotic cocktail consisting of 100 g/ml of ampicillin, gentamycin, neomycin and metronidazole, and 50 g/ml of vancomycin for 7 days eliminated colony forming unit (CFU) over 99%. These chickens treated by certain concentration of antibiotics cocktail (ABX) were referred as ABX-treated chickens. There were no changes on physiological traits, for example, weight of body and immune organs (spleen, bursa and liver), length of intestine (duodenum, jejunum, ileum and large intestine) and the concentration of glucocorticoid in the serum. Furthermore, the population and MHC class II expression on B cells and macrophages in the cecal tonsils and spleen were not changed. I concluded that physiological traits, B cells and macrophages were not changed in ABX-treated chickens. The second, I examined whether subtype of CD4+ T cells was changed in ABX-treated chickens. In cecal tonsil, CD4+CD8–CD25+ and CD4+CD8+CD25+ T cells were significantly decreased in ABX-treated chickens, however these cells in the spleen were not changed. The expression of IL-10 and IFN-g was significantly decreased in CD4+CD8–CD25+ T cells from cecal tonsils of ABX-treated chickens. It was noting that CD4+CD8–CD25+ and CD4+CD8+CD25+ T cells from ABX-treated chickens did not suppress the proliferation of CD4+CD25– T cells. The reduction of CD4+CD8–CD25+ and CD4+CD8+CD25+ T cells in cecal tonsils from ABX-treated chickens expressed high level of CD5hi. Interestingly, the percentage of thymic CD4+CD8+CD25+ T cells was not changed in ABX-treated chickens. Conclusively, the population and suppressive function of peripheral CD4+CD8–CD25+ and CD4+CD8+CD25+ T cells decreased in ABX-treated chickens. The third, I examined what factors affected the population of CD4+CD8–CD25+ and CD4+CD8+CD25+ T cells. ABX-treated chickens co-housed with wild type chickens recovered the number of gut microbiota, and the proportion of CD4+CD8–CD25+ or CD4+CD8+CD25+ T cells in cecal tonsils to similar levels as those of wild type chickens. The results further showed that Gram-positive bacteria appeared to be responsible for the changes of CD4+CD8–CD25+ or CD4+CD8+CD25+ T cells in cecal tonsils. Feeding acetate, one of the short chain fatty acids, in ABX-treated chickens recovered CD4+CD8–CD25+ T cells and CD4+CD8+CD25+ T cells in cecal tonsils. Both butyrate and propionate did not show the effect to recover these cells. Interestingly, GPR43 mRNA level was highly expressed in CD4+CD8–CD25+ T cells. Conclusively, my study demonstrated that gut microbiota can regulate the population and suppressive function of CD4+CD8–CD25+ or CD4+CD8+CD25+ T cells, and acetate can induce CD4+CD8–CD25+ T cells in cecal tonsils via GPR43.