title: Intravenously injected sialidase inactivates attachment sites for lymphocytes on high endothelial venules.
abstract: Blood-borne lymphocytes initiate entry into secondary lymphoid organs, such as peripheral lymph nodes (PN) and gut-associated Peyer's patches (PP), by a highly specific adhesive interaction between the lymphocytes and the endothelium of specialized blood vessels known as a high endothelial venules (HEV). The selectivity with which functional subpopulations of lymphocytes migrate into particular lymphoid organs is believed to be regulated by the expression of cell adhesion receptors and complementary ligands on lymphocytes and HEV, respectively. The entry of lymphocytes into PN and PP has clearly been shown to involve distinct receptor-ligand pairs. Employing the Stamper-Woodruff in vitro adhesion assay, which measures lymphocyte attachment to HEV in cryostat-cut sections of lymphoid organs, we have previously shown that treatment of PN sections with two different sialidases inactivates HEV-adhesive ligands, whereas treatment of PP tissue sections has no effect on HEV-adhesive function. We now report that in vivo exposure of HEV to sialidase (after i.v. injection of the enzyme) also selectively prevents subsequent in vitro attachment of lymphocytes to PN HEV but not to PP HEV. Consistent with this organ-selective impairment of HEV-adhesive function by sialidase, i.v. injection of the enzyme is shown to prevent short term lymphocyte accumulation within peripheral lymph nodes while having no significant effect on accumulation in PP, blood, or nonlymphoid organs. Histologic examination with the sialic acid-specific lectin from Limax flavus verified that i.v. injected sialidase effectively removes stainable sialic acid moieties from HEV in both PN and PP. This study confirms that sialic acid is required for the adhesive function of PN HEV-ligands. A role for sialic acid as either a recognition determinant or as a regulatory molecule can be envisioned. In view of the fact that many pathogens release sialidase and cause substantially elevated serum levels of this enzyme, the present observations may have pathophysiologic significance. One mechanism by which such pathogens may avoid destruction is to inactivate susceptible HEV-ligands and disrupt the entry of lymphocytes into lymphoid organs where immune responses against the pathogens would normally be initiated.
authors.affiliation: Department of Anatomy, University of California, San Francisco 94143-0452.
authors.forename: S D
authors.initials: SD
authors.lastname: Rosen
authors.forename: S I
authors.initials: SI
authors.lastname: Chi
authors.forename: D D
authors.initials: DD
authors.lastname: True
authors.forename: M S
authors.initials: MS
authors.lastname: Singer
authors.forename: T A
authors.initials: TA
authors.lastname: Yednock
mesh_terms: D000818:Animals; D002448:Cell Adhesion / Q000187:drug effects*; D002465:Cell Movement / Q000187:drug effects; D004727:Endothelium / Q000187:drug effects*; D004729:Endothelium, Lymphatic / Q000032:analysis / Q000187:drug effects* / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry; D007275:Injections, Intravenous; D008214:Lymphocytes / Q000032:analysis / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D019158:N-Acetylneuraminic Acid; D009439:Neuraminidase / Q000008:administration & dosage*; D012794:Sialic Acids / Q000032:analysis
chemical_list: D012794:Sialic Acids; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid