Properties of Guinea Pig 7S Antibodies. VI. Transmission of Antibodies From Maternal to Fetal Circulation. ∗

Evidence provided by several investigators (1–4) suggests that in some animal species fetal membranes select certain maternal antibodies for transmission to the fetal circulation and exclude other antibody fractions. For example, in the human, 7SΓ ₂ antibodies reach the fetal circulation, but Γ _1A (β_2A) and Γ _1M (β _2M) antibodies appear to be excluded (1). In the rabbit and guinea pig, fetal membranes exposed to homologous and heterologous tetanus or diphtheria antitoxin transmitted the homologous antibody more readily than the heterologous antibody(2–4). Evidence has been presented that the process of selective transmission involves a property of piece III, obtained by papain digestion of 7S Γ-globulin(5). In contrast to the significant transmission of natural diphtheria antitoxin, pepsin-digested antitoxin, lacking a major part of piece III, was transmitted to the guinea pig and rabbit fetus in only trace amounts(2, 6). Conversely, fragment III of rabbit Γ-globulin was transmitted nearly as readily as whole Γ-globulin, whereas fragments II and I were transmitted only 1/5 and 1/10 as readily as fragment III(5).

Recent studies have characterized 2 types of guinea pig 7S antibody capable of reacting specifically with the same antigen but differing in electrophoretic mobility and biological properties(7,8,9). It was shown that guinea pig 7SΓ ₁ antibodies sensitized guinea pigs for passive systemic and cutaneous anaphylaxis; 7SΓ ₂ antibodies did not. Guinea pig 7SΓ ₂, but not 7SΓ ₁, antibodies fixed complement in vitro in the presence of antigen under the conditions tested and sensitized antigen-coated erythrocytes for lysis in the presence of complement. According to current concepts of the structure and function of mammalian Γ-globulins, differences between guinea pig 7SΓ ₁ and 7SΓ ₂ reside in the piece III (F fragment) of the antibody molecule(7). The availability of these 2 types of 7S antibodies led us to test (a) whether both antibodies were transferred through fetal membranes and (b) whether biologic properties associated with only one or the other of the antibodies would favor transmission or rejection by fetal membranes.