Molecular features of immunoreactive myelin basic protein in cerebrospinal fluid of persons with multiple slcerosis

The molecular weight of the myelin basic protein (BP)-like material appearing in cerebrospinal fluid (CSF) of 2 persons with active-phase multiple sclerosis (MS) and 3 with recent cerebral infarctions was determined by gel filtration chromatography under acidic conditions. Column fractions were examined by radioimmunoassay for BP peptide 43-88 antigen as well as for binding activity to BP. Material cross-reactive with BP peptide 43-88 eluted over a wide spectrum of molecular weights. Greater representation of lower molecular weight species occurred in MS. Fractionated CSF from 2 patients with MS and 2 with cerebral infarction contained binding activity, presumably antibody, to BP which was greater than that in unfractionated CSF. Binding to BP was also examined in unfractionated CSF from 70 persons, including 16 with MS and 36 with other neurological diseases. Although CSF from MS patients showed higher binding, the presence of BP binding activity was not specific for MS. Our findings suggest that the antigen cross-reacting with BP and its fragments in CSF appears in a spectrum of molecular weight species, with lower forms predominating in MS. The detection of binding activity to BP as well as its enhancement by treatment at low pH suggest that the BP-like antigen in CSF may exist in free as well as in complexed forms.