The C'1a-fixing properties of purified rabbit IgM anti-benzenearsonate antibody were determined. When tested with sheep erythrocytes to which hapten had been coupled by diazo linkage, the number of C'1a molecules fixed was 21% of the number of IgM antibody molecules bound to the erythrocyte surface. This was not due to loss of C'1a-fixing capacity during the purification procedure. Preparative electrophoresis of the antibody concentrated C'1a-fixing molecules in the anodal region so that antibody fractions with greater C'1a-fixing capacity were obtained. The demonstration that C'1a fixation is a property of a subpopulation of IgM molecules provides evidence for previously unrecognized µ-chain heterogeneity.
The development of tuberculin hypersensitivity in guinea pigs after BCG stimulation was suppressed by intramuscular administration of 50 mg/kg/day of 6-mercaptopurine started at the time of stimulation. Fasting of guinea pigs after BCG stimulation had no effect on the development of tuberculin hypersensitivity.
1. 6-Mercaptopurine (6-MP) prevents experimental allergic encephalomyelitis (EAE) during the period of drug administration in both rabbits and guinea pigs. The disease is suppressed even when treatment is started as late as the 5th day after antigenic stimulation in guinea pigs and the 12th day in rabbits. 2. After discontinuation of 6-MP treatment, there is a latent period before the disease is noted. The length of this latent period is not modified by the duration of 6-MP treatment. 3. The effect of 6-MP on EAE is not the result of leukopenia, non-specific toxicity and debilitation, anti-inflammatory activity, or mere masking of clinical signs of the disease. It is, rather, the result of 6-MP's specific anti-immunologic activity. 4. The effects of 6-MP on antibody production, delayed hypersensitivity, and EAE are compared. This provides indirect evidence for the importance of circulating antibody in the pathogenesis of EAE. 5. The important considerations in the use of 6-MP are discussed and the possible usefulness of 6-MP in human neurologic diseases is considered.