Postnatal development of dendritic reticulum cells and their immune complex trapping ability.

The postnatal development of dendritic reticulum cells in the rat popliteal lymph nodes was electron microscopically investigated in relation to the appearance of immune complex trapping capacity. The popliteal lymph nodes of neonatal rat consisted of loosely arranged fibroblastic reticulum cells. In the following stage, the peripheral cortex and paracortex became distinguishable. The former was made up of an accumulation of small lymphocytes, scattered within a framework of reticulum cells. On te 28 th day, the first primary follicle appeared in the peripheral cortex. Simultaneously the immune complex could be trapped on the cytoplasmic membrane of reticulum cells, which were located in the central portion of the primary follicles. The early image of germinal centers appeared corresponding to immune complex trapping areas. In the well-developed secondary follicles, the immune complex trapping cells were mainly localized in the cap area. Their cytoplasmic membranes formed the dendritic processes, on which the distinct ability of trapping of the immune complex was recognized. It was demonstrated that the fibroblastic reticulum cells, forming the stroma of lymph nodes, were transformed into the typical dendritic reticulum cells with labyrinth structures in the cap area. Desmosomal junctions were often found, not only between the dendritic reticulum cells themselves, but also between the dendritic reticulum cells and lymphocytes. We suggest that the desmosomal junctions play a role as the channel for a transmission of immunological information.