Background: We have shown in previous studies the presence of a patchy pattern of lactase protein expression in the proximal jejunum of hypolactasic humans, adult rabbits, and rats. The present study investigated the mechanisms underlying the heterogeneous expression of lactase on the villus.
Methods: Proximal jejunal tissue from 18 adult humans and 12 adult rabbits was examined using enzymocytochemical and surface-staining techniques for lactase protein and activity.
Results: In the proximal jejunum of hypolactasic humans and adult rabbits, lactase activity is patchily distributed on the villus enterocytes. In humans, the patches of lactase-positive enterocytes are randomly distributed on the villus, whereas in rabbits, vertical, continuous sheets of positive enterocytes arise from the base of the villus.
Conclusions: The presence of enterocytes without lactase activity is one of the mechanisms causing adult-type hypolactasia in the proximal jejunum of humans and mammals. The patchy pattern of lactase in rabbits suggests a clonal origin with heterogeneity of the cells arising from the crypts. In hypolactasic humans, the enterocyte heterogeneity occurs as a consequence of mechanisms that do not have a clonal origin.