Facial nerve transection causes expansion of myelin autoreactive T cells in regional lymph nodes and T cell homing to the facial nucleus.

Nervous tissue expression of immunological signal and recognition molecules, as well as lymphoid tissue immune responses after facial nerve trauma was studied in male rats of the Lewis and Brown Norway (BN) strains. In both rat strains nerve transection caused within four days the appearance of IFN-gamma-like immunoreactivity in the cytoplasm of axotomized motor neurons and an induction of MHC class I and II, and CD4 molecules on surrounding glial cells to a similar extent. T lymphocytes also infiltrated the facial nuclei ipsilateral to the axotomy in all animals. The number of autoreactive T cells in superficial cervical lymph nodes, which in response to whole myelin or peptides of myelin basic protein (MBP) secreted IFN-gamma increased markedly after axotomy. This response was more conspicuous in Lewis rats, which are susceptible to experimental allergic encephalomyelitis (EAE), than in BN rats, which are EAE resistant. A proportion of the axotomized Lewis rats also developed widespread perivascular infiltration of mononuclear cells in the CNS, reminiscent of EAE. Hypothetically, a strong expansion of myelin autoreactive IFN-gamma producing T cells secondary to nerve trauma may have immunopathological consequences in genetically predisposed individuals. It is also possible that myelin reactive T cells, whether recruited to the lesioned nerve, could have impact on macrophage function during Wallerian degeneration in the distal stump.