A subset of Schwann cells in peripheral nerves contain a 50-kDa protein antigenically related to astrocyte intermediate filaments

Antisera raised to the astrocyte intermediate filament structural protein stained elements in the peripheral nerves of several species. These elements were not associated with myelinated nerve fibers, were more common in splenic and vagus nerves than in the sciatic nerve, and persisted after nerve transection. In teased nerve preparations antigen-positive cells appeared to be the Schwann cells that surround small diameter, unmyelinated axons. Absorption of the antiserum with purified rat spinal cord 50-kDa protein or with bovine splenic nerve cytoskeletal extract blocked the reaction with CNS astrocyte processes or with PNS nerve fibers. Immunoblots of cytoskeletal preparations of bovine splenic nerve or rat sciatic nerve showed that the antigen from peripheral nerves comigrated at 50 kDa with antigen from bovine or rat spinal cord or cultured rat astrocytes. The CNS and PNS 50-kDa proteins from bovine tissues were subjected to limited digestion with Staphylococcus aureus protease V8. After separation on SDS-gels, antigenic peptides were detected by immunoblotting. The pattern of antigenic peptides for the CNS and PNS proteins were identical. We conclude that Schwann cells associated with nonmyelinated axons contain a cytoskeletal protein that is the same size and has the same peptide map as the major structural protein of astrocyte intermediate filaments.