ONTOGENY OF LA-MESSENGER RNA IN THE MOUSE SMALL-INTESTINAL EPITHELIUM IS MODULATED BY AGE OF WEANING AND DIET

Background: Exogenous antigenic peptides are presented to T cells by class II major histocompatibility complex (la) molecules on the surface of antigen-presenting cells. Class II-associated invariant chain (li) is also required for effective antigen presentation. Because messenger RNAs (mRNAs) for li chain and for class II l-Aβ chain appear in the mouse intestinal epithelium after weaning, experiments were conducted to test the effect of age of weaning and diet on the appearance of la and li mRNA. Methods: Four litters were split at day 17; one half was weaned and the other remained with the mother until day 24. On day 23, 25, 27, and 29, enterocytes were isolated from full-length small intestine by vascular perfusion with 30 mmol/L ethylenediaminetetraacetic acid, and the RNA was extracted. Results: Appearance of li and l-Aβ was significantly delayed by late weaning, as judged by RNA hybridization blots (li chain) and complementary DNA amplification (l-Aβ chain). In mice on elemental diets, the appearance of li and l-Aβ chain was delayed compared with littermates reared on standard chow, li mRNA failed to appear in mice maintained on the elemental diet by day 40, despite normal growth. Conclusions: Appearance of mRNA for both la and li depends on the introduction of a complex diet and not the "stress" of weaning or elimination of breast milk. Introduction of foreign dietary antigens or development of an altered intestinal flora may contribute to this process. © 1993.