CHARACTERIZATION OF PERIVASCULAR CELLS IN ASTROCYTIC TUMORS AND PERITUMORAL EDEMATOUS BRAIN

Perivascular cells (PVCs) form an immunophenotypically defined populat ion that plays an important scavenging role in the perivascular fluid drainage pathways in the rat brain; such cells may also act as antigen -presenting cells. The present study tests the hypotheses that (a) PVC s in human brain are distinct from microglia and haematogenous macroph ages, and (b) PVCs within astrocytic tumours and peritumoral oedematou s brain tissue react in a similar way to PVCs in the rat brain, Paraff in sections of formalin-fixed tissue from 10 astrocytomas, 10 anaplast ic astrocytomas, 10 glioblastoma multiforme, peritumoral oedematous br ain and from normal human brain were examined immunocytochemically usi ng antibodies HLA-DR beta-chain for MHC class II antigen, PGM1 and MAC 387 directed against macrophage components, MT1 for T lymphocytes and GFAP for astrocytes. No PVCs, microglia or macrophages were labelled by these techniques in paraffin sections of normal brain. Microglia, m acrophages recently derived from haematogenous monocytes and PVCs were labelled by immunocytochemistry in all tumours but were more numerous in glioblastomas than in astrocytomas or anaplastic astrocytomas. Per ivascular cells were distinguished by their perivascular position, the ir expression of MHC class II antigen and were labelled by PGM1 antibo dy but not by MAC 387 antibody. Microglia and monocyte/macrophages, re mote from blood vessels, on the other hand, were strongly labelled by MAC 387, moderately by PGM1 and showed weak expression of MHC class IT antigen. A similar pattern of staining was seen in peritumoral oedema tous tissue. These findings suggest that PVCs form a defined populatio n of resident cells in the human brain and that they are distinct from microglia, monocytes and macrophages, Furthermore, upregulation of MH C class II and PGM1 expression on PVCs in tumours and oedematous brain , suggest that they play a similar scavenging role in the human brain to that seen in the rat brain.