Dependence on antigen dose and timing in the immune response of C3H mice to malignant ascites cells.

This study presents evidence suggesting that the immune response to malignant ascites cells exists in some state of balance, which seems to be regulated by the dose of antigen and the time used for immunization. Injection s.c. of high doses of tumour cells weekly for 5 weeks afforded protection against a subsequent i.p. tumour graft. Immunization by the same route with a 100-fold lesser amount of the tumour also induced immunity, but along with factors able to abrogate the effect of this immunity. These tumour-specific factors were able to reduce the binding to the cell membrane of specific antibodies detectable in the indirect immunofluorescence test and to protect the tumour cells against complement-dependent cytotoxic activity present in the tumour fluid. The factors interacted with protein A at pH 8.0, suggesting that they share properties with immunoglobulins. The factors eluted in the same fractions as IgG from Sephadex G-200 and showed high affinity for membrane associated antigens.