FACS analysis of lymphocyte subpopulations illustrates the stimulating effect of gut microbiota and LPS-rich sterile diet. (A) Both gut microbiota and the LPS-rich diet decrease the proportion of CD19+ B cells in MLNs. (B) LPS-rich diet induces the expansion of CD4+ T cells in MLNs and spleen. (C) Microbial stimulation does not affect the proportion of CD8+ T cells. (D) Both gut microbiota and the LPS-rich sterile diet induce the expansion of Foxp3-expressing CD4+ T cells in MLNs. (E) The ratio of CD4+Foxp3- T cells to CD4+Foxp3+ T cells remains constant in all lymphoid organs. (F) Gut microbiota stimulate the expansion of Foxp3-expressing CD8+ T cells in PPs and MLNs. Results represent the mean (± SE) of at least 10 mice/group. Statistical analyses were performed using one-way analysis of variance (ANOVA) and a post-hoc comparison test (Tukey-Kramer). * indicates p < 0.05 and ** indicates p < 0.01.