A derivative of myelin-associated glycoprotein in cerebrospinal fluid of normal subjects and patients with neurological disease.
A procedure for quantitating the myelin-associated glycoprotein (MAG) in cerebrospinal fluid (CSF) was developed. The procedure involved immunoprecipitation with rabbit polyclonal anti-MAG antiserum followed by immune staining of electroblots with the monoclonal antibody HNK-1. This method could detect as little as 2 ng of MAG per ml of CSF and could accurately measure levels of 5 ng/ml or greater. No intact MAG was detected in any of the CSF samples examined, but all samples contained the 90K dalton proteolytic derivative of MAG called dMAG. Samples from normal volunteers and patients with demyelinating diseases contained levels of dMAG ranging from 2 to 13 ng/ml. There was no correlation of dMAG levels with levels of myelin basic protein or with active demyelinating disease. The relatively high levels of dMAG, even in control CSF samples, probably resulted from normal physiological turnover of MAG and could possibly obscure any additional increments of MAG or dMAG release that might occur as a result of demyelination.