Microtubule-associated protein 2 (MAP-2) is expressed in low and high grade diffuse astrocytomas

The expression of neuronal antigens in diffuse astrocytomas has not been thoroughly evaluated. We have investigated the expression of microtubule associated protein 2 (MAP-2), synaptophysin and non-phosphorylated epitopes of neurofilament protein (NFP) by immunohistochemistry in 15 low grade diffuse astrocytomas and 15 glioblastomas. MAP-2 was strongly expressed in 97% of cases, using an antibody to both low and high molecular weight isoforms. An antibody specific to high molecular weight isoforms of MAP-2 (hmw-MAP-2) revealed weaker, focal staining in 60% of cases with greater expression in the glioblastomas (P=0.027). NFP was expressed in 50% of cases, but was generally weak and focal. There was little evidence of synaptophysin expression. We conclude that MAP-2 expression in astrocytomas is due predominantly to low molecular weight isoforms, which may be expressed in astrocytes as well as neurons. Focal expression of hmw-MAP-2 and NFP, however, suggest that neuronal antigens may be expressed, particularly in high grade astrocytomas. Immunopositivity for these antigens should not preclude the diagnosis of diffuse astrocytoma.