The transfer of IgG from serum to CSF, evaluated by means of a naturally occurring antibody.

Titres in CSF of natural IgG antibodies (AB) to rabbit erythrocytes (RRBC) correlated well with titres in serum in normal individuals, indication a passive transfer of the Ab. The ratio of CSF Ab to serum Ab mostly found was 1:400. The ratios of total IgG were slightly lower than the ratios of Ab to RRBC in normal individuals and in the majority of the diseases, except in multiple sclerosis and in subacute sclerosing panencephalitis (SSPE) where the ratios of total IgG were markedly elevated, indicating production of IgG in the central nervous system. In SSPE the ratio of measles Ab was even more elevated, suggesting that these antibodies contribute to the local IgG production. The ratios of Ab to RRBC in the two diseases were not elevated, or only slightly elevated. In normal and pathological CSF and in the Ab to RRBC all subclasses of IgG were found. In conclusion, the Ab to RRBC are considered convenient markers of serum IgG in the CSF.