Dendritic reticulum cells of lymph nodes in the rat using zinc iodide - osmium technique

ABSTRACT

Ten adult Sprague - Dawly rats of both sexes, weighing between 180 - 220 g were used in this study. They were maintained under convential laboratory conditions with free access to water and commercial rat food. The morphological architecture of dendritic reticulum cells [DRCs] in the rat lymph nodes was studied by light and electron microscopy after tissue impregnation and staining by zinc iodide-osmium [ZIO] method. DRCs represented the main stromal cell population. These cells were located both in the cortex and in the medulla and exhibited various configurations. In the cortex they appeared elongated and fusiform in shape with slender and long dendritic processes that ramify in a complex fashion. They were observed in the lymphoid follicles [especially in the germinal centre], lymphatic sinuses and the deep cortex, the DRCs were detected in close association with the subcapsular sinus, they might be located just underneath the sinus endothelium or directly share in forming the sinus lining. In the medulla, the DRCs appeared irregular in shape with coarse or delicate cytoplasmic processes forming an extensive cellular reticulum. This cellular reticulum spanned the region between the sinuses and the blood vessels such as capillaries and / or high endothelial venules [HEVs]. In this instance they were organized in a discontinuous sheath - like fashion around the vessel wall. By light and electron microscopy, DRCs have been observed to come in close spatial relationship with each other and with various other cell types including small, medium sized and large lymphocytes, lymphoblasts, plasma cells, interdigitating cells, sinus endothelial cells, the endothelium of HEVs and capillaries. These microanatomical features were consitent with the proposal that DRCs might be involved in the communicative networks between the different lymph node compartments. In particular, DRCs were thought to provide efficient anatomical arrangements which influence the lymphocyte traffic patterns and might be involved in the transport of molecules from the sinus compartment to the HEVs or to the distinct cell populations in the lymphoid parenchyma. From the previous data, it was suggested that the DRCs serve as accessory cells for the development of immune responses. Further studies should be performed to clarify the role of these cells in the regulation of lymphocyte mediated immunity