Scanning electron microscopic studies of reticular framework in the rat mesenteric lymph node

Abstract

The reticular framework in the lymph node has in the past been studied mainly by light microscopy of silver-impregnated specimens. The aim of the present study is to understand three-dimensionally the ultrastructure and organization of the reticular framework better than before. The mesenteric lymph nodes of the rat were prepared either an alkali-water maceration method or a conventional method and were observed in a scanning electron microscope (SEM). The SEM study of alkali-water macerated tissues visualized directly the reticular fiber network in the lymph node. The reticular fibers consisted of thin bundles of collagen fibrils. They were continuous with the collagen fibrillar sheaths of blood vessels and lymphatic sinuses as well as with the fibrous capusule, thus acting as a skeleton of the lymph node. The arrangement of the reticulum was variable, depending on individual compartments. The SEM study of conventionally treated tissues, on the other hand, clarified the shape of reticular cells and their relationship with the reticular fibers. The sinus reticular cells connected with the sinus lining cells but separated from the parenchymal reticular cells, indicating that the former two originate from lymphatic endothelial cells. The parenchymal reticular cells varied in shape depending on their locations but essentially shared features with fibroblasts. The arrangements of the reticular fibers in the parenchyma were closely related to the associated reticular cells, showing the possibility that the reticular cells maintain the shape of the reticular framework suitable for each compartment of the lymph node.