Passive enhancement of mouse skin allografts by alloantibodies is Fc dependent.

The capacity of F(ab')2 fragments of alloantibodies to enhance mouse allografts was studied in B6AF1 recipients of B10.D2 skin grafts. F(ab')2 obtained by digestion of B6AF1 anti-B10.D2 antibodies was purified by means of affinity chromatography, with anti-subclass antisera and protein A. The degree of contaminating IgG was less than 0.02%. Administration of F(ab')2 with an antigen-binding capacity similar to the IgG from which it originated, inhibited acute antibody-mediated graft rejection but was unable to induce enhancement. Even a dose that was 130 times the molar amount of the minimal enhancing dose of undigested IgG2 was ineffective. We conclude, therefore, that passive enhancement of mouse skin allografts by alloantibodies requires the Fc part.