Binding of homologous and heterologous IgG to Fc receptors on the fetal rabbit yolk sac membrane.

Abstract

Abstract Quantitative measurements were made of the in vitro binding of 125I-labeled rabbit serum IgG and serum IgG from 10 other mammalian species to Fc receptors on the fetal rabbit yolk sac membrane (YSM). The experiments were carried out as described earlier. The amount of IgG bound (μg/3.5 cm2 YSM disc) was greatest for the homologous system and less for each of the heterologous IgG: rabbit, 33; guinea pig, 29; mouse, 22; rat, 20; dog, 10; human, 5; and sheep, 9; pig, 4; horse, 2; goat, 2; cow, 2. The inference from these results is that IgG from animals such as guinea pig, mouse, and rat, of the phylogenetic order Rodentia, an order closely related to that of the rabbit, Lagomorpha, display receptor-recognition structural units in their Fc regions, similar to that of rabbit, whereas the Fc regions of IgG from ungulates (sheep, pig, horse, goat, cow) bear little resemblance to that of the rabbit in this respect. The binding of IgG from dog (Carnivora) and man (Primata) falls between the other two groups. These data are consistent with the current concept that in the ungulates, transfer across the neonatal gut is nonspecific, whereas in Lagomorpha, Rodentia, Carnivora, and Primata, the transfer of IgG from mother to young is a Fc-governed specific process.