A study on binding of suspended nodal lymphocytes to high endothelial venules in sections of frozen rat lymph nodes.

Live lymphocytes were previously shown to bind selectively to endothelial cells (HEV cells) of the high endothelial venules (HEVs) in sections of frozen lymph nodes. This study examines aspects of the assay that have so far not been considered or which have been incompletely addressed. It was found that bound lymphocytes form a cytoplasmic veil, and that about half of them form small groups in which they are linked together by cytoplasmic bridges. It was also found that at least 83% of the lymphocytes bind to HEV walls, but very unevenly, and that 5% also bind to medullary venules. In addition, 31% of the lymphocytes were estimated to bind to the abluminal face of HEV cells and probably to tissue lymphocytes present in subendothelial spaces or in perivascular channels (spaces). This would reflect cell interactions occurring, in vivo, between HEV cells and/or subendothelial lymphocytes. It is suggested that antigen specificity of lymphocyte retention by HEV cells accounts for the uneven binding to HEVs.