title: Enriched immune-environment of blood-brain barrier deficient areas of normal adult rats.
abstract: The circumventricular organs (CVOs) in the brain are without a blood-brain barrier (BBB) and as such directly exposed to blood plasma constituents and blood-borne pathogens. In light of previous studies showing discrepancies regarding the immunocompetence of these organs, we initiated the present study to provide a comprehensive immunohistochemical analysis of the cellular expression of immune-associated antigens within the pineal gland, area postrema and the subfornical organ. In all CVOs, subpopulations of cells morphologically similar to complement receptor type 3 immunoreactive microglial/macrophage cells expressed major histocompatibility complex (MHC) class II antigen, leucocyte common antigen (LCA/CD45), as well as CD4 and ED1 antigen. Based on morphological criteria the MHC class II antigen expressing cells could be grouped into a major population of classical parenchymal and perivascular ramified microglial cells and a minor population presenting itself as scattered or small groups of rounded macrophage-like cells. CD4 and ED1 antigen were expressed by both cell types. CD45 was preferentially expressed by macrophage-like cells. MHC class I antigen was expressed by the vascular endothelium in both BBB-protected and BBB-deficient areas and was additionally present as a lattice-like network throughout the BBB-deficient parenchyma in all CVOs. The results suggest that the BBB-free areas of the brain besides being constantly surveyed by blood-borne macrophages, possess an intrinsic immune surveillance system based on resting and activated microglial cells, which may function as a non-endothelial, cellular barrier against blood-borne pathogens.
authors.affiliation: Department of Anatomy and Cell Biology, University of Odense, Denmark. erikbo@imbmed.ou.dk
authors.forename: E B
authors.initials: EB
authors.lastname: Pedersen
authors.forename: J A
authors.initials: JA
authors.lastname: McNulty
authors.forename: A J
authors.initials: AJ
authors.lastname: Castro
authors.forename: L M
authors.initials: LM
authors.lastname: Fox
authors.forename: J
authors.initials: J
authors.lastname: Zimmer
authors.forename: B
authors.initials: B
authors.lastname: Finsen
mesh_terms: D000818:Animals; D001812:Blood-Brain Barrier; D001921:Brain / Q000276:immunology*; D018845:CD11 Antigens / Q000032:analysis; D015704:CD4 Antigens / Q000032:analysis; D015395:Histocompatibility Antigens Class I / Q000032:analysis*; D000949:Histocompatibility Antigens Class II / Q000032:analysis*; D007074:Immunoglobulin G / Q000032:analysis; D007150:Immunohistochemistry; D017493:Leukocyte Common Antigens / Q000032:analysis; D008297:Male; D017628:Microglia / Q000737:chemistry; D051381:Rats; D011921:Rats, Inbred WKY
chemical_list: D018845:CD11 Antigens; D015704:CD4 Antigens; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G; D017493:Leukocyte Common Antigens