Appearance of the reticular cells which trap antigens in the rat lymph node in postnatal development

The cells binding and retaining immune complexes on their cell surface existed in rat lymph nodes with no germinal centers. This study attempted to clarify the relationship between the two types of cells, reticular cells and follicular dendritic cells (FDCs), in the rat lymph node at early stages of postnatal development by immuno-electron microscopy on anti-horseradish peroxidase (HRP) and HRP injected rat. On the 19th and 23rd day after birth, germinal centers were not yet constructed nor were typical FDCs visible. However, immune complex binding cells were observed on the 23rd day, and not on the 19th. HRP reactive materials (immune complexes) were localized between lymphocytes and large lucent cells, making meshworks. They were revealed by electron microscopy on the cell surface which invaginated into the cytoplasm. The HRP reactive cells extended their cytoplasmic processes and formed a connection by their processes. They were reticular cells which enclosed reticular fibers by their cytoplasmic processes or contacted with reticular fibers closely. The reticular cells may be precursors of the FDCs.