[CK20 expression in the gastrointestinal tract of the embryo and fetus].
A novel type of cytokeratin, cytokeratin 20 (CK20), was added in 1990 to the classic catalog of human cytokeratins, a heterogeneous group of proteins present in almost all epithelia. In man, the expression of CK20 is almost entirely confined to the gastro-intestinal epithelium, to the urothelium and to Merkel cells. Since only few data are available regarding the expression of CK20 in the developing human intestinal mucosa, we studied CK20 immunoreactivity in fetal and neonatal human gut. Immunoreactivity for CK20 was tested in fetuses and newborns, from the twelfth up to the fortieth week of gestation. In each subject, a specimen from the oesophagus, stomach, small intestine, colon, appendix was studied. Tissue samples were routinely processed and paraffin sections were stained with the CK20-specific antibody IT-Ks 20.8. CK20 immunoreactivity was absent in the oesophageal epithelium and it was unevenly distributed in the gastrointestinal mucosa. Three main patterns of immunoreactivity were observed during normal development: the first, found in the stomach and in the small bowel, is characterized by a progressive increase in CK20 expression during gestation; the second pattern, found in the duodenum, shows a progressive decrease in CK20 expression during gestation; in colon and appendix (third pattern), we did not find significant changes in the degree of immunoreactivity for CK20 during gestation. CK20 is unevenly expressed in developing human intestinal mucosa. The degree of positivity for CK20 appears to be related to the epithelial maturation stage only in gastric and small bowel mucosa. Further studies are needed to verify if the uneven CK20 immunoreactivity in the gastrointestinal tract persists even in adulthood.