Immunolocalization of a mesenchymal antigen specific to the gastrointestinal tract

The aim of the present study was to localize, at the fine structural level, a protein found by indirect immunofluorescence to be associated with the mesenchymal tissue 1) closely applied to the intervillus epithelium before the formation of intestinal crypts in the mouse fetus and 2) around intestinal crypts during and after their formation.

We used a pre-embedding immunolabeling technique for extracellular matrix molecules, and a monoclonal antibody (Mab) directed against antigen MIM-1/130.

Immunofluorescence disclosed the presence of antigen 1/130 in the connective tissue closely applied to the epithelium of the gallbladder, pyloric glands, and intestinal and colonic crypts in adult mice. The antigen was absent in all salivary glands, kidney, liver, lung, spleen, and pancreas. At the fine structural level, gold particles in positive organs were associated with the interstitial matrix around collagen fibrils underneath the epithelia; gold particles were completely absent in the basement membranes. In the small intestine, labeling was seen only around crypts from cell position 1 up to the crypt-villus junction; it was totally absent under the villus epithelium. In order to confirm this particular localization in vivo, Mab 1/130 was administered orogastrically to 9-day-old mice: after 3 hours the antibody was found lining the immediate periphery of duodenal crypts as seen by indirect immunofluorescence. In control animals, an anti-mouse laminin Mab of the same subclass as Mab 1/130 was orogastrically fed using the same protocol: basal laminae were labeled under the epithelium of duodenal villi and crypts and also in the lamina propria, with a decreasing gradient from the top of the villi to the bottom of the crypts.

These observations indicate that the extracellular matrix associated with the epithelium of pyloric glands, of intestinal and colonic crypts, and of gallbladder contains a new antigen whose function remains to be determined. The neonatal mouse hence constitutes a good model to study the role of extracellular matrix components in determining organ differentiation in vivo.