| Research Abstract |
The localization of two lymphocyte homing ligands, L-selectin ligand (LSL) and MAdCAM-1, were studied immuno-histochemically in order to reveal the mechanisms of the lymphocyte extravasation through the high endothelial venules (HEV) within the secondary lymphoid tissues. Most HEV within the peripheral lymph nodes (PLN) expressed LSL. Although the submandibular and deep cervical lymph nodes are PLN, some HEV in these lymph nodes expressed MAdCAM-1.In nasal associated lymphoid tissue (NALT), many HEV expressed LSL, while a few HEV expressed MAdCAM-1, showing an expression profile distinct from that of HEV in Peyer's patches, gut mucosal associated lymphoid tissues.
Perfusion of the rat inguinal lymph nodes with a culture medium was performed to remove blood except for adhered lymphocytes to the HEV and to observe early morphological changes of the adhered lymphocytes and high endothelial cells (HEC). The HEV of the lymph nodes were observed by scanning and transmission electron microscopy. Adhered lymphocytes were considered to be round with many microvilli on their whole surface. Lymphocytes were then seemed to retract most microvilli other than those attached to the HEC on their tips. Next, lymphocytes were considered to become flatter to adhere to HEC with broader surfaces. These morphological changes might reflect the transition from the weak adhesion mediated by L-selectin and its ligands to the strong adhesion by LFA-1 and ICAM-1.The uneven distribution of microvilli on the some transforming lymphocytes suggests important roles of the microvilli in transition of the adhesion modes.
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