Guinea pig 7Sγ2 antibodies were demonstrated to fix complement in the presence of antigen and to sensitize antigen-coated, tanned erythrocytes for lysis in the presence of complement; guinea pig 7Sγ1 antibodies did not participate in these reactions. Gamma-2 antibodies were more efficient in provoking hemorrhagic necrosis in reverse passive Arthus reactions than equal amounts of non-complement-fixing gamma-1 antibodies. Unlike anaphylaxis in the guinea pig, both guinea pig 7Sγ1 and 7Sγ2 antibodies provoked passive cutaneous anaphylactic reactions in the rat.
Efficient hemolytic activity attributable to 7S guinea pig anti-sheep erythrocyte antibodies migrated faster than the peak of complement-fixing activity, but slower than the peak of PCA activity in starch block electrophoresis. It is uncertain whether this activity is a function of a third type of antibody produced in response to the particulate property of the antigen or whether it is due to the antigenic heterogeneity of the erythrocyte cell membrane.