Expression of J1/tenascin in the crypt-villus unit of adult mouse small intestine: implications for its role in epithelial cell shedding

The localization of the extracellular matrix recognition molecule J1/tenascin was investigated in the crypt-villus unit of the adult mouse ileum by immunoelectron microscopic techniques. In the villus region, J1/tenascin was detected strongly in the extracellular matrix (ECM) between fibroblasts of the lamina propria. It was generally absent in the ECM at the interface between subepithelial fibroblasts and intestinal epithelium, except for some restricted areas along the epithelial basal lamina of villi, but not of crypts. These restricted areas corresponded approximately to the basal part of one epithelial cell. In J1/tenascin-positive areas, epithelial cells contacted the basal lamina with numerous microvillus-like processes, whereas in J1/tenascin-negative areas the basal surface membranes of epithelial cells contacted their basal lamina in a smooth and continuous apposition. In order to characterize the functional role of J1/tenascin in the interaction between epithelial cells and ECM, the intestinal epithelial cell line HT-29 was tested for its ability to adhere to different ECM components. Cells adhered to substratum-immobilized fibronectin, laminin and collagen types I to IV, but not to J1/tenascin. When laminin or collagen types I to IV were mixed with J1/tenascin, cell adhesion was as effective as without J1/tenascin. However, adhesion was completely abolished when cells were offered a mixture of fibronectin and J1/tenascin as substratum. The ability of J1/tenascin to reduce the adhesion of intestinal epithelial cells to their fibronectin-containing basal lamina suggests that J1/tenascin may be involved in the process of physiological cell shedding from the villus.

Langerhans’ Granules in Cells of an Eosinophilic Histiocytoma

Recent papers describe Langerhans’ granules in cells of normal skin, in Letterer-Siwe disease, and associated with osseous and pulmonary lesions of histiocytosis X. The present report concerns the structure and occurrence of these granules in a solitary tumor of the human posterior anal wall, diagnosed as an eosinophilic histiocytoma, confirmed by the electron microscopy. The investigation supports the hypothesis that the epidermal Langerhans’ cell is a macrophage. Samples of the recurrent tumor were fixed in cacodylate-buffered 6.4% glutaraldehyde, washed in cacodylate-buffered 0.2M sucrose, and postfixed in OSO4 for electron microscopy. Embedment was in Araldite, and sections were contrasted with uranyl acetate and lead hydroxide.The surface of the tumor cells was very irregular, with numerous microvillus-like projections, and was without both desmosomes and basement membrane. The nuclei were lobulated, and possessed both finely dispersed and coagulated chromatin, with multiple nucleoli. The system of parallel tubules and sacs which composed the Golgi was prominent in most cells. Numerous linear profiles of RER occurred. The RNA particles were also abundant throughout the cytoplasm in groups unrelated to the RER. Centrioles were seen frequently paranuclearly. The mitochondria, with well developed cristae, were frequently altered, being locally swollen, vacuolated or containing myelin figures, Fig. A. The most striking organelles were (i) the Langerhans’ granules (L), observed in abundance throughout the cytoplasm of most of the tumor cells, but predominantly in those cells which contained (ii) the fusiform or ovoid, membrane-bound, electron-dense bodies (B). Many of these rounded, dense bodies contained concentric, double-membranous structures, Figs. C and D.