Ultrastructural localization of extracellular matrix proteins of the lymph node cortex: evidence supporting the reticular network as a pathway for lymphocyte migration.
BACKGROUND
The lymph node (LN) is a crossroads of blood and lymphatic vessels allowing circulating lymphocytes to efficiently recognize foreign molecules displayed on antigen presenting cells. Increasing evidence indicates that after crossing high endothelial venules, lymphocytes migrate within the node along the reticular network (RN), a scaffold of fibers enwrapped by fibroblastic reticular cells (FRC). Light microscopy has shown that the RN contains specific extracellular matrix (ECM) proteins, which are putative molecular "footholds" for migration, and are known ligands for lymphocyte integrin adhesion receptors.


RESULTS
To investigate whether ECM proteins of the RN are present on the outer surface of the FRC and are thus accessible to migrating lymphocytes, ultrastructural immunohistochemical staining of cynomolgus monkey LN was performed using antibodies to human ECM proteins that were successfully employed at the light microscopic level. The fibrillar collagens I and III were observed primarily within the reticular network fibers themselves. In contrast, the matrix proteins laminin, fibronectin, collagen IV, and tenascin were observed within the reticular fibers and also on the outer membrane surface of the FRC.


CONCLUSIONS
These findings suggest a molecular basis for how the RN functions as a pathway for lymphocyte migration within the lymph node.
Sobocinski
Gregg P
GP
MCDB Dept, University of Michigan, Ann Arbor, MI, USA.
Toy
Katherine
K
Bobrowski
Walter F
WF
Shaw
Stephen
S
Anderson
Arthur O
AO
Kaldjian
Eric P
EP
D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D002465:Cell Movement; D024042:Collagen Type I / Q000378:metabolism*; D024061:Collagen Type III / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000276:immunology / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D007150:Immunohistochemistry; D008198:Lymph Nodes / Q000033:anatomy & histology / Q000648:ultrastructure*; D008214:Lymphocytes / Q000502:physiology; D008252:Macaca fascicularis; D008854:Microscopy, Electron; D012155:Reticulin / Q000378:metabolism / Q000648:ultrastructure*
D000911:Antibodies, Monoclonal; D024042:Collagen Type I; D024061:Collagen Type III; D016326:Extracellular Matrix Proteins; D012155:Reticulin