AN IMMUNOHISTOCHEMICAL STUDY OF P53 AND PROLIFERATING CELL NUCLEAR ANTIGEN EXPRESSION IN PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY

Nuclear p53 immunoreactivity is demonstrated in infected oligodendrogl ia, as well as in a proportion of reactive and bizarre astrocytes, in seven progressive multifocal leukoencephalopathy (PML) biopsies. This likely represents binding to, and prolongation of the half-life of, wi ld-type p53 protein by JC virus T-antigen. Other possible mechanisms a re considered. The same cells show proliferating cell nuclear antigen (PCNA) positivity, as do a proportion of morphologically normal oligod endroglia and astrocytes, reflecting proliferating populations of thes e glial sub-types. It is possible that functional inactivation of p53 in non-lytically infected astrocytes may allow neoplastic astrocyte cl ones to emerge. However, p53 and PCNA immunoreactivity per se cannot b e regarded as indicative of neoplasia in PML, and caution must be exer cised in the interpretation of such nuclear staining profiles.