AIM: To explore the characteristics of T cell activation and regulatory T cells derived from murine Peyer's patches through comparative studies on Peyer's patches, mesenteric lymph nodes and inguinal lymph nodes. METHODS: Signal cell suspendsions were prepared from murine mesenteric lymph nodes (MLNs), the Peyer's patches (PPs) and inguinal lymph nodes (ILNs), respectively. The percentage of cell subpopulations such as CD3+ T cells, CD3+CD4+ helper T cells and regulatory T cells (Treg, CD4+CD25+) were analyzed. Lymphocytes were activated by polyclonal stimulators such as concanavalin (Con A), phorbol 12, 13-dibutyrate (PDB) only, and PDB plus ionomycin (Ion). The expression of CD69 (the early marker of CD3+ T cell activation) was measured by FACS. RESULTS: A lower ratio of CD3+ T cells was seen in PPs than those in MLNs and ILNs. The ratios of CD3+ CD4+ T cells to CD3+ T cells in PPs, MLNs and ILNs were almost the same. A higher rate of Treg was seen in CD4+ T cells from the PPs as compared with those from MLNs and ILNs. A higher percentage of activated CD3+ T cells derived from the PPs cultured without polyclonal stimulators were detected as compared to MLNs and ILNs, while lower responsiveness of CD3+ T cells from the PPs stimulated by Con A was seen as compared with those from MLNs and ILNs. CONCLUSIONS: The lower rate of CD3+ T cells as well as higher rate of Treg in PPs was due to its desensitization. The higher rate of basic activated state in CD3+ T cells from the PPs indicated that the T cells were activated by enteric antigens in physiological conditions. The lower responsiveness of activation to some polyclonal stimulators probably reveals that the T cells are in a state of anergy. All the characteristics mentioned above contribute to prevent pathological inflammations and maintain tolerance to enteric antigens such as food proteins and commensal bacteria but simultaneously retain proper immune responses to pathogenic microbes.