Fluid and cellular pathways of rat lymph nodes in relation to lymphatic labyrinths and Aquaporin-1 expression

Abstract

The aim of the present study was to examine the organization of lymph fluid and cellular pathways and distribution of the membrane water channel Aquaporin-1 (AQP-1) in rat lymph nodes. Lymph fluid and cellular pathways within lymph nodes were examined by fluorescent protein tracer/confocal microscopy and by scanning electron microscopy (SEM), While the distribution of AQP-1 was studied immunohistochemically. Tracer studies showed the subcapsular sinuses continued directly at the hilum or via the intermediate sinuses to the medullary sinuses, and lymphatic labyrinths originating with blind-ends in the deep cortex drained into medullary sinuses. Afferent lymph tracers were also observed in node cortex interstitium. By SEM, lymphatic labyrinths appeared densely filled with lymphocytes and had few intraluminal sinus reticular cells, while medullary sinuses possessed well-developed networks of sinus reticular cells. The presence of many lymphocytes wedged in the walls of the lymphatic labyrinth suggested that lymphocytes migrate between the node parenchyma and lymphatic labyrinths. AQP-1 was distributed on the membrane of lymphatic endothelium and reticular cells as well as on both luminal and abluminal cell membranes of high endothelial venules (HEVs). Our SEM findings support the concept that lymphocytes migrate from the node parenchyma into lymphatic labyrinths in the deep cortex. The nodal distribution of AQP-1 plus the presence of a polarized distribution of ion pumps and/or ion channels in the HEV endothelium hypothesized in our discussion could explain the mechanism of the reported lymph-to-plasma fluid flux in lymph nodes and also facilitate the entry of afferent lymph antigens into the node cortex interstitium.

Structure and function of rat lymph nodes

“…Our scanning electron microscopic observation showed the three-dimensional organization of the lymph nodes (Ushiki, Ohtani, Abe, 1995;Ohtani et al, 2003) (Fig. 2).…”

“…In order to clarify the complex structure of lymph nodes, we have re-examined the node structure by immunohistochemistry to LYVE-1, which is integrated with our previous findings by scanning electron microscopy of intact tissues, immunohistochemistry to AQP-1, and tracer studies using fluorescent-labeled gelatin (Ohtani et al, 2003). In this study we used rabbit polyclonal antibodies to LYVE-1 (Abcam, California) and rabbit anti-AQP-1 antibodies (Chemicon International, Temecula).…”

Fluid Flow Regulates Stromal Cell Organization and CCL21 Expression in a Tissue-Engineered Lymph Node Microenvironment

“…Fluid flow through the functional LN is an omnipresent mechanical force acting on the resident TRCs that line the permeable conduits through which lymph is continuously transported (13,20,44). Increased lymph flow is an immediate response to tissue injury or inflammation (21)(22)(23)(24)(25)(26)(27), and presumably there is a lack of flow through LNs that are blocked or that drain from dysfunctional lymphatic vessels.…”

Recent Developments in Morphology of Lymphatic Vessels and Lymph Nodes

“…Water may be absorbed from the HEV wall into the blood vessels, because a water channel called Aquaporine-1 is strongly expressed near the surface of the endothelial cells of HEVs. 22) This suggests a functional intravenous shunt of lymphatic vessels in the lymph node.…”

“…The lymph node consists of a lumen surrounded by lymphatic endothelial cells and parenchyma, featuring a reticular structure filled with lymphocytes, etc. 22) In the parenchyma, the cortex is connected to myelin through the deep cortex. The afferent lymphatic vessels flow into the cortical lymphatic sinuses.…”