KERATIN INTERMEDIATE FILAMENT EXPRESSION IN ASTROCYTIC NEOPLASMS - ANALYSIS BY IMMUNOCYTOCHEMISTRY, WESTERN-BLOT, AND NORTHERN HYBRIDIZATION

In this study, 29 formalin-fixed, paraffin-embedded astrocytic tumors were analyzed immunocytochemically with the antikeratin monoclonal ant ibodies Mak-6 and Cam 5.2 and a polyclonal antibody against glial fibr illary acidic protein (GFAP). Immunoreactivity for Mak-6 was present i n 29 cases (100%) including six well-differentiated astrocytomas, nine anaplastic astrocytomas, and 14 glioblastomas multiforme. Cam 5.2 imm unoreactivity was focally present in one case of GBM (4%) but was abse nt in the remaining 28 cases. All cases were immunoreactive with an an tibody against GFAP. Cytokeratin (CK) expression was examined in extra cts of four separate well-characterized astrocytoma cell lines by West ern blotting with the monoclonal antibodies Mak-6, Cam 5.2, and anti-C K 18 and by Northern analysis using a cDNA probe for the human CK 18 g ene. The Western blots revealed the presence of immunoreactive bands c orresponding to CK numbers 14/15, 16, and 18 in extracts from all four cell lines and additional bands corresponding to CK 8 in 3/4 lines an d CK 19 in 1/4 lines. Northern analysis detected CK 18 mRNA in extract s from 2/4 astrocytic cell lines. These findings demonstrate that CK i mmunoreactivity is frequent in astrocytic tumors and confirm through t he molecular and biochemical analysis of CK 18 gene expression and of keratin intermediate filament proteins that the basis for CK immunorea ctivity in astrocytic tumors is bona fide CK expression, not cross-rea ctivity with other antigens or artifact. The demonstration of CK expre ssion by astrocytic neoplasms has important implications for pathologi sts involved in the diagnosis of poorly differentiated tumors.