Schwann cell undergoes apoptosis during experimental allergic neuritis (EAN)

Schwann cell apoptosis is not detectable in the normal mature mammalian peripheral nervous system (PNS). However during PNS cell-mediated demyelination, apoptosis contributes to the elimination of endoneurial T- lymphocytes. We report here that approximately 10% of Schwann cells die by apoptosis during the early phases of recovery from experimental autoimmune neuritis (EAN) in the adult rat, a model for the Guillain-Barre syndrome. Schwann cell apoptosis, follows endoneurial T-cell clearance, and is prominent in the nerve roots, the site of most severe segmental demyelination, but is rare in the more distal regions of the PNS, where Wallerian degeneration predominates. Further immunological analysis showed that the p75 neurotrophin receptor (p75NTR) is expressed in 2% of both apoptotic and non apoptotic Schwann cells, while Ki-67, a marker of cell proliferation, is expressed in 20% of apoptotic and in 1% of non apoptotic Schwann cells. Our new observations indicate that apoptosis during cell- mediated demyelination can be a phenomenon related either to the development or the recovery of autoimmune cell mediated inflammation.