Ultrastructural and immunohistochemical segregation of gemistocytic subsets.

Gemistocytes are frequently encountered in cases of reactive gliosis as well as in glial tumors. Recently, miniature forms of gemistocytes (minigemistocytes) were recognized as cellular constituents of oligodendrogliomas. Antibodies specific for the intermediate filaments glial fibrillary acidic protein and vimentin are reactive with gemistocytic cells, but do not react specifically with these cells. In a study of 23 glial tumors we found the monoclonal antibody Pm43 selectively reactive with the classical gemistocytes as well as with the minigemistocytes. Nevertheless, at the ultrastructural level a striking difference in the arrangement of the glial filaments between both gemistocytic cell types was found. Immunoelectron microscopy showed that the reactivity for the newly discovered gemistocytic marker Pm43 was confined to identical intermediate filaments. Despite immunohistochemical homology, a clearly different ultrastructure divides classic gemistocytes and minigemistocytes into two subsets.