Expression of MHC class II (Ia) antigen by the neonatal enterocyte : the effect of treatment with interferon-gamma

Immunohistochemical techniques were used to probe the expression and inducibility of class II major histocompatibility complex (MHC) (Ia) antigens by the mouse enterocyte at various stages postpartum. Expression of Ia was related to both age and intestinal location. Ia antigen was not detected until at least 1 week post-weaning and was noted thereafter in both proximal and distal intestine. Both crypt and villus enterocytes were stained in the distal small intestine, but staining was restricted to the upper portion of the villus in the proximal small intestine. Moreover, the extent of staining and the intensity of staining were greater in the distal small intestine. The effect of a single injection of recombinant mouse interferon-gamma (IFN-gamma) on Ia expression by enterocytes of 16-day-old, suckling BDF1 mice was examined. Injection of distilled water (DW) or 1 to 2 x 10(4) U IFN-gamma did not induce enterocyte Ia expression. Doses of 4-10 x 10(4) U were effective inducers of Ia on crypt and, occasionally, on lower villus cells examined 24 hr later. Staining did not persist on the enterocyte beyond 48 hr. In conclusion, Ia is not normally expressed on small intestinal enterocytes of the mouse until after weaning; however, Ia expression can be induced earlier by treatment with IFN-gamma. It is not known whether failure to detect Ia expression prior to weaning reflects a lack of positive stimuli and/or the presence of inhibitory stimuli, possibly carried in the breast milk.