Immunological enhancement of a murine tumor allograft by passive alloantibody IgG and F(ab')2.

The F(ab')2 fraction of an anti-tumor IgG alloantiserum induced passive enhancement of tumor allografts in inbred mice about as well as did intact IgG; i.e. apparently the Fc fragment is not required for suppressing cellular immunity. Passive F(ab')2, however, was somewhat less efficient than intact IgG or whole alloantiserum in depressing the allohemagglutinin response. The latter finding is in accord with previous observations on the relative inefficiency of F(ab')2 in feedback inhibition of the humoral response of mice to a heteroantigen.