Complexus adhaerentes, a new group of desmoplakin-containing junctions in endothelial cells: II. Different types of lymphatic vessels.

In diverse mammalian species, including (man, cow and rat) the very flat endothelial cells of lymphatic vessels of various organs, including the retothelial meshwork of sinus of lymph nodes, are connected by zonula-like plaque-bearing junctions which differ from the similarly structured junctions of blood vessel endothelia by the presence of desmoplakin or an as yet unknown but closely related plaque protein. These extended junctions, which also contain plakoglobin but none of the presently known desmogleins and desmocollins, are therefore different from the spot-like desmosomes (maculae adhaerentes) present in epithelia, myocardium and dendritic reticulum cells of lymphatic follicles, and are collectively subsumed under the new category of complexus adhaerentes, including the 'syndesmos' connecting the processes of the retothelial cells. The lymphatic endothelial cells possessing these special desmoplakin-containing junctions also contain the calcium-dependent transmembrane glycoproteins, V-cadherin and cadherin 5, of which the latter has also been partly localized to regions with desmoplakin-positive junctions. Possible functional reasons for the formation and maintenance of complexus adhaerentes are discussed as well as the potential value of reagents which allow their identification in relation to physiology and pathology.