| Summary: | To investigate the possibility of local antigen presentation within the peripheral nerve in amyotrophic lateral sclerosis (ALS), cryostat sections of 83 peripheral nerve biopsies were stained for the demonstration of HLA-DR using a monoclonal antibody. Forty samples showed increased expression of HLA-DR in endoneurium. The phenotypic characteristics of the HLA-DR positive cells are chiefly Schwann cells, using S-100 protein as a marker. We did not detect any co-expression between HLA-DR and NF (axons) and HLA-DR and myelin marker. We also detected co-expression between HLA-DR and NGFr in a majority of HLA-DR positive cells. Inflammatory cells were infrequent, being detected only in 11 cases, predominantly around epineurial blood vessels. Motor and sensory nerve biopsies performed simultaneously showed higher expression of HLA-DR in motor nerves in 2 out of 4 patients. The significance of these findings is not clear. The presence of endoneurial cells expressing HLA-DR suggests that an autoimmune mechanism may be involved in ALS having Schwann as the main target.
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