Immunocytochemical study of myelin-associated glycoprotein (MAG) and basic protein (BP) in acute experimental...

To compare distributions of oligodendroglial myelin-associated glycoprotein (MAG) and myelin basic protein (BP) during demyelination in acute experimental allergic encephalomyelitis (EAE). Lewis rats were sensitized with an emulsion containing guinea pig spinal cord and complete Freund's adjuvant. The rats were examined clinically and groups were perfused with fixative before symptoms appeared (7d), within 48 h of symptom onset (10d) and during more severe illness (14d, 21d). Paraffin sections of cerebrum, brainstem, and spinal cord were immunostained with antisera to MAG and BP. Other sections in each serially mounted series were stained with luxol fast blue, hematoxylin and eosin or with the Bodian method to correlate MAG and BP results with histological changes. No abnormalities were detected 7d after sensitization. After 10d, small perivenular inflammatory cell infiltrates were present in white matter, displaced myelinated fibers, but their MAG stained periaxonal regions and BP-stained myelin sheaths appeared normal. In pontine grey matter lesions, there were focal abnormalities in a few myelin sheaths. After 21d, demyelinating lesions were present that were largest in pontine grey matter. Decreased MAG staining was present in areas of myelin sheath loss. MAG-stained fragments were found in zones of active myelin breakdown but no decrease or other change in MAG staining extended beyond the margins of demyelinating lesions into areas with normally stained myelin sheaths. Thus, in contrast to multiple sclerosis (Itoyama et al. 1980), changes in periaxonal oligodendroglial MAG are not present in acute EAE before inflammatory cell infiltrates or myelin sheath changes appear. Our findings suggest that myelin sheaths are the primary targets in EAE-induced demyelination. Oligodendroglia appear to be relatively unaffected and are available to remyelinate axons.