Passive enhancement of mouse tumor allografts by alloantibodies is Fc-dependent.

Enhancement of growth of a B10.D2 fibrosarcoma in B6AF1 recipients could be induced by administration of B6AF1 anti-B10.D2 lymphocyte serum. The role of the Fc part in this phenomenon was studied by treatment of the B6AF1 recipients with F(ab')2 fragments of enhancing alloantibodies. A highly purified F(ab')2 preparation was used to exclude any effects of undigested IgG. Administration of F(ab')2 did not lead to enhancement of the tumor allografts, not even when given in a dose that was 22 times the molar amount of the lowest enhancing dose of undigested IgG. We therefore conclude that passive enhancement of mouse tumor allografts by alloantibodies is Fc dependent.