Differential induction of major histocompatibility complex molecules on mouse intestine by bacterial colonization.

The aim of this study was to determine what factors induce major histocompatibility complex (MHC) molecules on the mouse small intestinal epithelium by using immunohistochemical methods. In germ-free mice, although MHC class I molecules such as H-2K and thymus leukemia antigen (TLa) were expressed on the small intestinal epithelium, class II molecules were absent. The introduction of microorganisms into germ-free mice induced characteristic MHC molecules on the small intestinal epithelial cells. The I-A molecule was induced on the villus tip and crypt epithelial cells 7 days after conventionalization, and the I-E molecule was induced on the mid villus and crypt epithelial cells 14 days after conventionalization. The staining intensity of the H-2K molecules was increased 4 days after conventionalization. In contrast, TLa did not change during conventionalization of germ-free mice. These results suggest that the expression of MHC molecules, except for the TLa, is greatly dependent on the presence of intestinal microorganisms.