Cell contacts and polysomes in irradiated human jejunal mucosa at onset of epithelial repair.

Epithelial ultrastructure was studied in the jejunal biopsies of irradiated cancer patients at early stages of mucosal regeneration 1 to 3 days after completing treatment. Major changes in the typical atrophic areas lacking villi were the following: (1) Cell contacts were loose between surface epithelial cells lacking signs of degeneration with extracellular gaps visible between the lateral membrane interdigitations. (2) Numerous processes from such epithelial cells extended into the underlying basement membranes and sometimes, especially in crypt areas, came into close contact with processes from underlying mesenchymal cells. (3) The epithelial cells often had enlarged nucleoli with granular threads. Increased amounts of epithelial cells were also seen with numerous membrane-free polysomes. The study suggests that at the onset of jejunal epithelial regeneration in man an epitheliomesenchymal cell interaction takes place similar to that described in normal gut development in laboratory animals. The possible significance of the close contacts between epithelial and mesenchymal cells, also seen in crypt areas of regenerated epithelium, is discussed in the light of mechanisms proposed for tissue interactions. The noticed increase in polysomes is interpreted as a morphologic sign of activated protein synthesis in the differentiating cells of the epithelium.