Counteracting roles of MHCI and CD8(+) T cells in the peripheral and central nervous system of ALS SOD1(G93A) mice

BACKGROUND: The major histocompatibility complex I (MHCI) is a key molecule for the interaction of mononucleated cells with CD8(+)T lymphocytes. We previously showed that MHCI is upregulated in the spinal cord microglia and motor axons of transgenic SOD1(G93A) mice. METHODS: To assess the role of MHCI in the disease, we examined transgenic SOD1(G93A) mice crossbred with β2 microglobulin-deficient mice, which express little if any MHCI on the cell surface and are defective for CD8(+) T cells. RESULTS: The lack of MHCI and CD8(+) T cells in the sciatic nerve affects the motor axon stability, anticipating the muscle atrophy and the disease onset. In contrast, MHCI depletion in resident microglia and the lack of CD8(+) T cell infiltration in the spinal cord protect the cervical motor neurons delaying the paralysis of forelimbs and prolonging the survival of SOD1(G93A) mice. CONCLUSIONS: We provided straightforward evidence for a dual role of MHCI in the peripheral nervous system (PNS) compared to the CNS, pointing out regional and temporal differences in the clinical responses of ALS mice. These findings offer a possible explanation for the failure of systemic immunomodulatory treatments and suggest new potential strategies to prevent the progression of ALS. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13024-018-0271-7) contains supplementary material, which is available to authorized users.