Murine Intestinal Bacteria Modulate Antigen-Specific Cytokine Production by Intestinal Immune Cells Derived from Germ-Free TCR-Transgenic Mice

Abstract

We have previously established germ-free ovalbumin- (OVA) specific T cell receptor transgenic (OVA-Tg) mice to examine the direct effects of intestinal bacteria on intestinal immune responses to dietary antigen. We prepared the intestinal immune cells from Peyer’s patches and lamina propria in the small intestine derived from germ-free (GF) or conventional (CV) mice, and demonstrated that the immunocytes from GF mice showed higher cytokine production in response to OVA antigen compared with those from CV mice. This suggested that intestinal bacteria could regulate cytokine production in response to OVA antigen. In this study, we investigated the effects of stimulation of antigen presenting cells (APCs) by intestinal bacteria on antigen-specific immune responses by using germ-free OVA-Tg mice. Lactobacillus and Bacteroides, which were isolated from murine intestinal bacteria, were inactivated by UV exposure. Thy1.2⁻ cells, APCs of mesenteric lymph nodes (MLN) representing the gut associated lymphoid tissues, and MLN CD4⁺ T cells were prepared from GF Balb/c and OVA-Tg mice respectively. These cells were co-cultured with OVA and intestinal bacteria, and cytokines (IFN-γ, IL-10) in the supernatants were then assayed by ELISA. Both Lactobacillus and Bacteroidess enhanced OVA-specific cytokine production when the cells were stimulated with bacteria and OVA together. On the other hand, the pre-stimulation of APCs with Lactobacillus down-regulated OVA-specific cytokine production by CD4⁺ T cells. However Bacteroides did not enhance OVA-specific IFN-γ production significantly. These results suggested that Lactobacillus might modulate antigen-specific T cell responses via APCs differently from Bacteroides.