Serum antibodies against cytosol antigens in multiple sclerosis

Immunologically pure IgG was isolated from serum of multiple sclerosis (MS) patients and normal controls. The F(ab)2 moiety of IgG was then isolated by salting out between 12.5 and 19.0% Na2SO4 of the pepsin digest of IgG. The ability of the 131I-labelled F(ab)2 to bind to subcellular brain fractions (nuclei, synaptosomes, mitochondria, myelin, microsomes and cytosol) of MS and control brains was assayed and expressed as radioactivity/mg protein of respective fractions. No significant difference could be traced with regard to F(ab)2 binding to the particulate fractions from MS patients and normal controls. MS F(ab)2 did, however, bind about two times more to MS cytosol than to non-MS cytosol antigens and up to 50% more MS than the control F(ab)2 did bind to the MS cytosol. MS F(ab)2 and control F(ab)2 did bind equally to control cytosol. The immunoprecipitate of MS F(ab)2-MS-cytosol was isolated and used for immunization of rabbits. The antiserum formed could be demonstrated by means of crossed immunoelectrophoresis to contain antibodies to one to three MS antigens. Thus it must be concluded that MS serum contains antibodies to one to three MS antigens occurring in MS brain cytosol.