Laminins, tenascin and type VII collagen in colorectal mucosa.

The distribution of different laminin polypeptides, type VII collagen and tenascin has been studied in adult and foetal colorectal mucosa by using the indirect immunofluorescence technique. Immunoreactivity for laminin alpha 1 chain was located to basement membranes of epithelia, muscularis mucosae, and blood vessels, respectively in different segments of adult colon and rectum. Laminin beta 1 and gamma 1 chains were additionally expressed in lamina propria. Laminin alpha 2 chain was also found in lamina propria around the pericryptal fibroblasts. Immunoreactivity for laminin beta 2 chain was restricted to basement membranes in the muscularis mucosae and arteries. Laminin alpha 3 and beta 3 chains, suggestive for laminin-5, were confined especially to surface epithelial basement membranes. Immunoreactivity for type VII collagen was confined to basement membrane of surface epithelium in a punctate manner, while that for tenascin was seen slightly more broadly in the basement membrane zone and also in the muscular layer. The distribution of laminin chains in 16-week-foetal colon mostly resembled that of corresponding adult tissue, although immunoreactivities for laminin alpha 2 and beta 2 chains were lacking. Type VII collagen and the high molecular weight isoform of tenascin were also absent from the foetal colon. The results show that the basement membrane of the surface epithelium of colon and rectum express the components of epithelial adhesion complex, laminin-5 (alpha 3-beta 3-gamma 2) and type VII collagen, resembling in this respect small intestine and stomach while laminin-2 (alpha 2-beta 1-gamma 1) appears to be associated with pericryptal fibroblasts, and laminin-1 (alpha 1-beta 1-gamma 1) widely in most basement membranes.