Protection of rats from experimental allergic encephalomyelitis with antiserum to guinea-pig spinal cord.

Inbred AS rats were immunized with guinea-pig spinal cord. The severity of experimental allergic encephalomyelitis (EAE) was studied in groups treated with antiserum to guinea-pig spinal cord and control groups treated with antiserum to other guinea-pig tissue. Prolonged treatment throughout the experiment strikingly reduced the severity of the clinical disease. Early treatment for the first 8 days after immunization had a similar protective effect. Late treatment starting on the 10th day after immunization did not produce significant protection. Protection was produced by antiserum from both EAE-resistant and EAE-susceptible strains. The protective effect of the serum did not correlate with the presence of haemagglutinating antibodies to basic protein or the titre of complement-fixing antibodies to galactocerebroside. These results suggest that antiserum to undefined central nervous system antigens contains an `enhancing' antibody which inhibits a relatively early stage of the immune response causing EAE.