Antibodies to myelin-associated glycoprotein (MAG) in the cerebrospinal fluid of multiple sclerosis patients.

Cerebrospinal fluids (CSF) and sera from patients with multiple sclerosis (MS), other neurological diseases (ONDs) and healthy controls were tested for antibodies to myelin-associated glycoprotein (MAG) by several different assays. Using a very sensitive, solid-phase radioimmunoassay with radioiodinated protein A, a statistically significant elevation of anti-MAG antibodies was detected in MS CSFs in comparison to those from ONDs and healthy controls. The antibodies reacted with human MAG, but not with rat MAG, and appeared to be directed towards carbohydrate determinants in the glycoprotein. The CSFs from high IgG producers had significantly greater anti-MAG antibody levels than those from low IgG producers, even though the assays were done on CSF samples that had been normalized to the same IgG concentration. The elevated antibodies were not detected when the same samples were tested with a liquid-phase radioimmunoassay or an enzyme-linked immunosorbent assay, and the antibodies in the MS CSF also could not be detected by Western blotting. An elevated level of antibodies was not found in sera from MS patients by any of the assays, possibly because these samples gave higher and more variable background. The results suggest that there is a low level of humoral immunity to MAG in MS patients that can only be detected by the most sensitive assays. This weak immune response to MAG may be secondary to the demyelinating process, but could play a role in the progression of the disease.