Organization of the reticular network of rabbit Peyer's patches.

The organization of the network of collagen fibers of rabbit Peyer's patches was examined by scanning electron microscopy (SEM) in alkali-water macerated tissues. The relationship between this network and the reticular cells within it was further studied by SEM of ultrasonicated tissues. Collagen fibrils (about 60 nm in diameter) formed collagen fibers or sheets. There were sheets of collagen fibrils with numerous pores beneath the patch dome epithelium. Within the patches, collagen fibers repeatedly divided and fused, forming the reticular network. The reticular network within the follicle was looser than within the dome, the corona, or the interfollicular area. The latter three compartments showed similar structures and consisted of numerous intercommunicating small subcompartments. Reticular cells were in contact with groups of free cells lodged in these subcompartments within the reticular network. Reticular cell processes with numerous fenestrations embraced not only collage fibers forming the reticular network, but also sheaths of collagen fibers of blood and lymphatic vessels. Sheaths of collagen fibers of high endothelial venules and lymphatic vessels were also fenestrated, indicating the sites through which lymphocytes and other free cells migrate. These results indicate that the reticular network of Peyer's patches is organized so as to facilitate migration and lodging of free cells and thus facilitate antigen-to-cell and cell-to-cell interactions during an immune response. The naked areas on the collagen fibers seem to provide a scaffolding for free cells during their migration.