Fine structures of the medulla-like tissues and the lymph sinuses in the lymph nodes of pig.

Abstract

Fine structures of the "Medulla-like tissue (MT)" and the lymph sinuses facing the MT of pig lymph nodes were studied by electron microscopy. The MT consisted mainly of reticular cells and strands of collagen fibers, and there were no obvious structures of the so-called medullary sinuses. In the MT of the cortico-medullary junction and near the sub-capsular lymph sinuses, there found the clusters of dendritic cells, which were furnished with a number of thin, elongated cytoplasmic processes connected to one another or to macrophages to form fine networks. In the sub-capsular areas of the MT where the efferent lymph vessels were restrictively absent, no genuine lymphatic sinuses were identified. The endothelial cells which configure the trabecular side of the peri-trabecular lymph sinuses (PTLS) were constantly covered with a basallamina and the surface of which has well-developed layer of collagen fibers. Inner walls of the sub-capsular lymph sinuses (SCLS) and parenchymal walls of the PTLS consisted of bi-layers of sinus lining cells with gaps and strands of collagen fibers. These results suggest that the MT in the pig lymph nodes has connective tissue-like structure, which is a characteristic ultrastructure, and enhances the filtration of materials and cellular elements in the pig lymph nodes.