Comparison of the characteristic features of Bonghan ducts, blood and lymphatic capillaries.

OBJECTIVE To show that the characteristic morphological and ultrastructural features of a Bonghan corpuscle and duct presented here are consistent with the description given in the early reports of Bonghan Kim. MATERIALS AND METHODS We compared the morphological aspects of Bonghan ducts with those of blood and lymphatic capillaries on the ultrastructural level to display the manifestly distinctive nature of the Bonghan system. RESULTS The walls of the ductules were observed to be composed of a single layer of endothelial cells with characteristic rod-shaped nuclei and were not surrounded by a basal lamina or by accessory cells, such as pericytes or smooth muscle cells. The abluminal cell membranes of Bonghan ductules were not attached by anchoring filaments to the fibers of extracellular matrices as observed in lymphatic capillaries. The cytoplasmic processes of ductule endothelial cells appear to form overlapping and interdigitated interconnections which completely lack junctional elements. Although the cytoplasm of ductule endothelial cells contained a well-developed rough endoplasmic reticulum and many free ribosomes and polysomes, there was a relatively small number of pinocytotic vesicles and lacks specific organelles, such as Weibel-Palade bodies. CONCLUSIONS The Bonghan corpuscles are specialized structures consisting of different types of immune cells randomly scattered as single cells in the matrix or clustered in follicle-like formations. Moreover, the Bonghan ductules in the corpuscle contain flowing immune cells and occasionally basophilic bodies.