Identification of a marker antigen for the endocytic stage of intestinal development in rat, sheep, and human.

Vacuolated enterocytes are highly endocytic epithelial cells present in intestines of diverse mammalian species during neonatal and/or fetal development. Using monoclonal antibodies raised against membrane fractions, we previously identified a 55-61 kd membrane glycoprotein that is restricted to apical endosomal tubules of vacuolated enterocytes in fetal and suckling rats. To determine whether this cell-specific antigen is present in vacuolated enterocytes of fetal sheep or humans, the endosomal antigen was immuno-affinity purifed from rats and used to generate and purify specific rabbit polyclonal antibodies. Light microcopic and electron microscopic immunocytochemistry showed that antigens cross-reactive with the rat endosomal antigen are present in vacuolated enterocytes of fetal sheep and fetal human small intestine and are restricted to apical endosomal tubules in these cells. Immunoblot analysis of tissue extracts from fetal human intestines showed antigen(s) at 55 and 60 kd, as well as a major form at 130 kd. Cross-reactive antigen(s) from fetal sheep intestines appeared as 42- and 50-kd bands. Although the molecular identities of the sheep and human antigens are not yet established, these results show that these antigens can serve as markers for the endocytic state of intestinal developmemt in humans as well as other mammals.