Immunoreactive phosphorylated epitopes on neurofilaments in neuronal perikarya may be obscured by tissue preprocessing

Monoclonal antibodies (SMI 31 and SMI 34) against phosphorylated epitopes on neurofilaments react almost exclusively with neuronal axons in paraffin sections of perfused animals. Using fresh frozen (unfixed) rodent brain sections the immunoreactivity with these antibodies was also present in numerous neuronal cell bodies. Both antibodies also recognized intracellular antigens in the soma of living cells of a human neuroblastoma clone. These data suggest that phosphorylation of neurofilaments in neuronal perikarya is common in vivo. The phosphorylated neurofilament epitopes in neuronal perikarya may become hidden during tissue preprocessing and fixation.