Immunophenotypic evidence for distinct populations of microglia in the rat hypothalamo-neurohypophysial system.
The morphology, distribution and immunophenotype of microglia throughout the adult rat hypothalamo-neurohypophysial system was examined. Four macrophage-associated antibodies (OX-42, F4/80, ED1 and ED2) were used; the expression of major histocompatibility complex antigens was investigated by use of antibodies against OX-6, OX-17 (MHC class II) and OX-18 (MHC class I). Three distinct types of microglia were identified. The first was located in the magnocellular nuclei; these 'radially branched' ('ramified') microglia had round cell bodies and long branched processes, and were strongly immunoreactive only for OX-42. The second was located outside the blood-brain barrier in the median eminence, pituitary stalk and neurohypophysis often close to blood vessels; these 'compact' microglia had irregular cell bodies and shorter processes, and were strongly labelled by OX-42 and F4/80, weakly labelled by OX-18, and generally unlabelled by ED1, ED2, OX-6 and OX-17. The third type was found in small numbers throughout the system at the surface of the nervous tissue or around blood vessels; these 'perivascular' microglia were elongated cells with no branching processes, and were strongly labelled by ED1, ED2, OX-18, OX-6, OX-17 and F4/80 antibodies but showed variable OX-42 immunoreactivity. Cells in a perivascular location were heterogeneous with respect to their immunophenotype. The presence in the normal adult rat hypothalamo-neurohypophysial system of MHC class-II molecules (OX-6 and OX-17) on a sub-set of perivascular microglia suggests that these cells are capable of presenting antigen to T lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)
Mander
T H
TH
Department of Human Anatomy, University of Oxford, UK.
Morris
J F
JF
D000818:Animals; D000954:Antigens, Surface / Q000032:analysis; D007030:Hypothalamo-Hypophyseal System / Q000166:cytology*; D007150:Immunohistochemistry; D016130:Immunophenotyping; D008297:Male; D017628:Microglia / Q000166:cytology* / Q000276:immunology; D051381:Rats
D000954:Antigens, Surface