Development of γδ T cell subset responses in gnotobiotic pigs infected with human rotaviruses and colonized with probiotic lactobacilli.

γδ T cell responses are induced by various viral and bacterial infections. Different γδ T cells contribute to activation and regulation of the inflammatory response and to epithelial repair. How γδ T cells respond to rotavirus infection and how the colonization of probiotics influences the γδ T cell response were unknown. In this study, we evaluated by multicolor flow cytometry the frequencies and distribution of total γδ T cells and three major subsets (CD2-CD8-, CD2+CD8- and CD2+CD8+) in ileum, spleen and blood of gnotobiotic (Gn) pigs at early (3-5 days) and late phases (28 days) after rotavirus infection. The Gn pigs were inoculated with the virulent human rotavirus Wa strain and colonized with a mixture of two strains of probiotics Lactobacillus acidophilus and Lactobacillus reuteri. In naïve pigs, the highest frequency of total γδ T cells was found in blood, followed by spleen and ileum at the early age (8-10 days old) whereas in older pigs (32 days of age) the highest frequency of total γδ T cells was found in ileum and spleen followed by blood. Rotavirus infection significantly increased frequencies of intestinal total γδ T cells and the putatively regulatory CD2+CD8+ γδ T cell subset and decreased frequencies of the putatively proinflammatory CD8- subsets in ileum, spleen and blood at post-infection days (PID) 3 or 5. The three γδ T cell subsets distributed and responded differently after rotavirus infection and/or lactobacilli colonization. The CD2+CD8+ subset contributed the most to the expansion of total γδ T cells after rotavirus infection in ileum because more than 77% of the total γδ T cells there were CD2+CD8+ cells. There was an additive effect between lactobacilli and rotavirus in inducing total γδ T cell expansion in ileum at PID 5. The overall effect of lactobacilli colonization versus rotavirus infection on frequencies of the CD2+CD8+ γδ T cell subset in ileum was similar; however, rotavirus-infected pigs maintained significantly higher frequencies of CD8- subsets in ileum than lactobacilli-colonized pigs. The dynamic γδ T cell responses suggest that γδ T cell subsets may play important roles in different stages of immune responses after rotavirus infection and probiotic colonization. The knowledge on the kinetics and distribution patterns of γδ T cell subsets in naïve pigs and after rotavirus infection or lactobacilli colonization provides the foundation for further mechanistic studies of their functions.