Immunocytochemical characterization of the A15 A5 transplantable brain tumour model in vivo.

A comparative immunocytochemical study was carried out on intracerebral and extracranial gliomas of the rat produced by intracerebral injection of low (10th) and high (40th) in vitro passages of neoplastic glial cells. The cells injected were a neoplastic astrocytic clone-A15 A5-derived from a mixed glioma induced transplacentally by N-ethyl-N-nitrosourea (ENU) in a BD-IX rat. An inverse relationship was seen between the expression of the astrocytic markers glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) at low and high passage: GFAP decreased with increasing passage while GS increased. The distribution of vimentin, the major cytoskeletal component of immature glia, was constant, irrespective of passage--a feature consistent with previous in vitro findings. The expression of laminin by both reactive and neoplastic astrocytes increased with increasing passage, while high magnification examination revealed the presence of the glycoprotein fibronectin on the cell-surfaces of A15 A5-derived tumour cells. Both neoplastic and reactive astrocytes expressed S-100 protein with a higher proportion of positive cells in extracranial tumours. Occasional cells, probably actively phagocytizing populations of reactive astrocytes and macrophages, were positive for alpha-1-antitrypsin. None of the neoplastic cells expressed the oligodendrocyte marker carbonic anhydrase II. This immunocytochemical study supports previous morphological findings in differences in differentiation between the cells of tumours produced by high and low passage cells.