Suppression of naturally occurring anti-tissue antibodies during growth and after removal of tumours.

The sera of normal rats were found to be active in the complement fixation test against isogeneic tumour homogenates. This activity was shown to be heat labile and to sediment with IgM globulins on zone ultracentrifugation in sucrose density gradients. Sera from rats bearing progressively growing tumours and sera from rats, which had such tumours excised, were found to be less active than normal rat sera in the complement fixation test against isogeneic tumour and liver homogenates. It was considered that this suppression of naturally occurring anti-tissue antibodies may be a specific process related to the host immune response to the tumour.