In Vitro Observation of the Effect of Intestinal Bacteria on IgA Production by Immunocytes in the Large Intestine: Comparison Between Germ-Free and Conventional Mice

Abstract

Previous studies comparing germ-free (GF) and conventional (CV) mice have shown that intestinal commensal microorganisms greatly affect the development of gut-associated lymphoid tissues and mucosal immune responses such as IgA production in the gut. Since there is a large number of intestinal microbiota, particularly in the large intestine, it is supposed that immunocytes in the large intestine are modulated by microbacteria. In this study, we investigated the immunomodulation of IgA production by intestinal microbacteria in the large intestine by comparing immunocytes from CV mice with those from GF mice. In GF mice, there were very few IgA plasma cells in lamina propria isolated from the large intestine (L-LP), but interestingly, greater numbers of IgA plasma cells were identified in lamina propria from the small intestine (S-LP). These findings suggested that IgA plasma cells in S-LP were stimulated by something other than intestinal commensal bacteria. We then found that the level of IgA production by L-LP IgA plasma cells isolated from GF mice was lower than that of CV mice. In addition, we examined the response of B220⁺ cells isolated from L-LP to LPS, a constituent of gram-negative bacteria. The result was that the B220⁺ cells from L-LP of GF mice produced IgA at lower levels than B220⁺ cells of CV mice. These data suggest that the IgA response in the large intestine is strongly induced by stimulation by intestinal microorganisms.