Immunoperoxidase staining of glial fibrillary acidic (GFA) protein polymerized in vitro: an ultramicroscopic study.

The unlabeled antibody peroxidase-antiperoxidase (PAP) method of Sternberger et al. has been employed at the ultramicroscopic level to stain filaments polymerized in vitro from aqueous extracts of multiple sclerosis (MS) plaques. The filaments were heavily decorated with antiserum to the glial fibrillary acidic (GFA) protein but not stained with serum absorbed with GFA protein, preimmunization serum, or anti-rat brain tubulin but was not stained with antiserum to the GFA protein. The present study provides direct morphological evidence that filaments polymerized in vitro from extracts of MS plaques contain the GFA protein.