Serological response to intracaecal injections of antigenic mouse tumour cells.

Immunofluorescence studies of sera from mice with induced enhancement of tumour growth demonstrated that these sera contained factors ("interfering factors") which in an apparently competitive manner interfered with the subsequent binding of specific antibodies to antigenic sites on the tumour-cell membrane. The factors were tumour-specific but lacked some of the immunoglobulin determinants. They could not be detected by polyvalent FITC-antimouse gamma-globulin. Interfering factors did not seem to be related to IgA or IgE. They were demonstrable in sera from tumour-free animals without growing tumours, thus differing from the tumour-specific "blocking factors".