The structure of the basement membrane of human lymph node high endothelial venules: an ultrastructural, histochemical and immunocytochemical study

Chondroitin sulfate proteoglycan at the basal lamina beneath high endothelial cells in human palatine tonsils: a light and electron microscopic study using the cationic colloidal iron method

The basal lamina of high endothelial venules (HEVs) in human palatine tonsils was intensely stained with cationic colloidal iron at pH 1.5 and with aldehyde fuchsin. This basal lamina exhibited a thick and double- or triple-layered structure forming small compartments, in which many lymphocytes were aligned. Digestion with hyaluronidase or collagenase eliminated both the colloidal iron and aldehyde fuchsin stainings of the basal lamina of HEVs. Treatment with chondroitinase ABC reduced colloidal iron staining, but did not interfere with the aldehyde fuchsin staining. Digestion with neuraminidase, keratanase, or heparitinase did not eliminate either the cationic colloidal or the aldehyde fuchsin staining. Digestion with neuraminidase reduced the colloidal iron staining on the luminal surface coat of the HEV. Electron microscopy of ultrathin sections revealed that cationic colloidal iron particles were deposited on the basal lamina of the HEV. The basal laminae of ordinary blood vessels were thin and single-layered, and stained only weakly with cationic colloidal iron. The present study suggests that negatively charged sites in the basal lamina of HEV derive mainly from a proteoglycan complex containing hyaluronic acid and chondroitin sulfate, which firmly binds collagen. This topochemical feature is suggested to be involved in the fascilitating migration of lymphocytes after passage through the endothelial layer.

Transendothelial migration of lymphocytes across high endothelial venules into lymph nodes is affected by metalloproteinases

The migration of lymphocytes from the bloodstream into lymph nodes (LNs) via high endothelial venules (HEVs) is a prerequisite for the detection of processed antigen on mature dendritic cells and the initiation of immune responses. The capture and arrest of lymphocytes from flowing blood is mediated by the multistep adhesion cascade, but the mechanisms that lymphocytes use to penetrate the endothelial lining and the basement membrane of HEVs are poorly understood. Matrix metalloproteinases (MMPs) control the metastatic spread of tumor cells by regulating the penetration blood vessel basement membranes. In this study, synthetic and natural inhibitors were used to determine the role of MMPs and MMP-related enzymes in regulating lymphocyte extravasation in mice. Mice were treated systemically with the hydroxamate-based MMP inhibitor Ro 31-9790 and plasma monitored for effective levels of Ro 31-9790, which block shedding of L-selectin. The total numbers of lymphocytes recruited into LNs were not altered, but L-selectin levels were higher in mice treated with Ro 31-9790. A reduced number of lymphocytes completed diapedesis and there was an increase in the number of lymphocytes in the endothelial cell lining, rather than the lumen or the basement membrane of HEVs. Lymphocyte migration and L-selectin expression in the spleen were not altered by Ro 31-9790 treatment. Two MMP inhibitors, TIMP1 and Ro 32-1541, did not block L-selectin shedding and had no effect on lymphocyte migration across HEVs. These results suggest that metalloproteinase activity is required for lymphocyte transmigration across HEVs into LNs and provide evidence for the concept that metalloproteinases are important players in some forms of transendothelial migration. (Blood. 2001;98:688-695)