A fibrillar elastic apparatus around human lymph capillaries

Abstract

A fibrillar elastic apparatus around the wall of human lymph capillaries is demonstrated by means of histochemical and ultrastructural techniques. This apparatus consists of three interlinked components listed here in order of increasing distance from the capillary wall: 1) oxytalan fibres connected to the abluminal surface of the endothelial cells, known also as "anchoring filaments" and consisting of bundles of microfibrils; 2) elaunin fibres consisting of microfibrils and a small amount of elastin; and 3) typical elastic fibres consisting of microfibrils and abundant elastin. The microfibrillar constituent has similar ultrastructural features in the three components of the elastic apparatus. Microfibrils have a diameter of 12-14 nm, an electron-transparent core and a wall with 3-5 electron-dense subunits and oblique cross striations with a period of 15-17 nm. Microfibrils are the common element of the three components of the elastic apparatus and they link them to one another and to the elastic network of the perivascular connective tissue. An elastic apparatus was not found around blood capillaries and it can thus provide a histological marker to identify lymph capillaries. The possible role of the lymphatic elastic apparatus in the physiological activity of the lymphatic absorbing network is discussed and it is proposed that its disconnection from the elastic network of the tissue may promote pathological conditions such as lymphoedema or diseases related to impaired immune responses.

Molecular characterization of lymphatic endothelial cells

“…This difference in response to collagen type I may reflect differences in the type of the extracellular matrix that each vessel type is exposed to in its natural environment. Blood vascular endothelium is in immediate contact with components of the basal lamina, whereas in lymphatic capillaries basal lamina is largely absent and LECs form an intimate association with adjacent interstitial tissue (5,9). In fact, one of the features that discriminate lymphatic capillaries from blood capillaries at the ultrastructural level are direct connections of LECs to the interstitial collagens by anchoring filaments (5,9).…”

“…Blood vascular endothelium is in immediate contact with components of the basal lamina, whereas in lymphatic capillaries basal lamina is largely absent and LECs form an intimate association with adjacent interstitial tissue (5,9). In fact, one of the features that discriminate lymphatic capillaries from blood capillaries at the ultrastructural level are direct connections of LECs to the interstitial collagens by anchoring filaments (5,9). Taken together, distinct expression patterns of vascular markers by cultured LECs and BECs and their differential responsiveness to the extracellular matrix and VEGF-C indicate that LECs and BECs represent distinct cell lineages which retain their differentiated phenotypes in culture.…”

“…30, 36, and 37). Finally, the lymphatic endothelial cytoskeleton is directly connected to the extracellular matrix by anchoring filaments composed mainly of elastin fiber microfibrils (9). Interestingly, an elastin microfibril protein (EMILIN) that is normally expressed in elastin-rich tissues (47) has been found to be selectively and abundantly expressed in LECs.…”

“…Whereas the junctions in blood vessels connect adjacent ECs over entire cell boundaries, the junctions in lymphatics are generally more sparse. Finally, one of the most striking characteristics of the lymphatic capillary is its integration within the interstitium; lymphatic ECs are connected to the extracellular matrix by fine strands of elastic fibers, i.e., anchoring filaments (5,(8)(9)(10).…”

Cell adhesion and integrin binding to recombinant human fibrillin‐1

“…They appear to connect endothelial cells to elastic fibers in the subendothelial matrix of the mouse aorta [10] and of lymphatic capillaries [11,12]. In the mouse aortic media the elastic laminae are linked to smooth muscle cells by bundles of microfibrils [13].…”