THE SINUS ENDOTHELIAL-CELL ARCHITECTURE IN THE MOUSE LYMPH-NODE - STRUCTURAL PECULIARITIES AND CLOSE CORRELATION WITH THE FIBROBLASTIC RETICULAR CELLS

The sinus endothelial cell architecture has been studied in the mouse lymph node by light and electron microscopy after tissue fixation with an osmium-zinc iodide mixture. This histochemical method allowed visu alization of sinus endothelial cells in the medullary and, partly in t he intermediate sinuses. The osmium-zinc iodide reaction also demonstr ated fibroblastic reticular cells, which represent the main stromal ce ll population in the lymph node and form the skeletal framework of the organ as well as the adventitia of sinuses. In the mouse lymph nodes, sinuses were lined by a simple layer of sinus endothelial cells whose integrity and continuity showed interruptions of various extension. I n areas devoid of complete sinus endothelial cell lining, fibroblastic reticular cells located in the nearly parenchyma were able to reach t he border of the sinus, being thus in direct contact with the lumen co ntent. Dendritic sinus endothelial cells as well as intermediate forms between sinus endothelial cells and fibroblastic reticular cells coul d be observed. The close structural characteristics that sinus endothe lial cells have in common with fibroblastic reticular cells and the fi nding of transitional cells with intermediate morphology between sinus endothelial cells and fibroblastic reticular cells, suggest a possibl e origin of sinus endothelial cells by migration and differentiation o f fibroblastic reticular cells located in the sinus adventitia.