The "intraendothelial canalicular formation": the route for lymphocyte diapedesisat the level of peripheral and mucosa-associated lymphoid tissue HEVs

How the lymphocyte crosses the blood endothelium during transendothelial
migration is demonstrated through the study of serial sections of high
endothelial venules (HEVs) of peripheral (mesenteric lymph nodes) and
mucosa-associated lymphoid tissue (Peyer's patches, vermiform appendix) during
normal lymphocyte homing and experimental intestinal inflammation. The sequence
of serial ultrastructural features of lymphocytes englobed in the endothelial
wall at different moments of transmigration made it possible to bring out that
their transendothelial migration toward the extracellular matrix of lymphoid
tissues occurs through an intraendothelial canalicular formation constituted by
two adjacent endothelial cells that have closed interendothelial junctions. This
intraendothelial canalicular formation, morphologically unlike the transcellular
and paracellular migratory pathways, is an innovative model of migratory route
for lymphocyte diapedesis that does not compromise the continuity of the
endothelial wall. The increased presence of lymphocytes and intraendothelial
canalicular formations during experimental inflammation and the metabolic
hyperactivity of the spring/summer months compared to the lethargic fast in
Chiropters underscores an influence on lymphocyte traffic through the HEVs of the
peripheral and mucosa-associated lymphoid tissue.