Maternal-foetal transfer of normal IgM in the rabbit.

Rabbits foetal sera harvested on the 28th day of gestation and sera from newborn rabbits were subjected to chromatography on Sephadex G-200. IgM and IgG were found in these sera. These immunoglobulins carried only maternal allotypic specificities and therefore, were not synthesized by the foetuses, but were transferred from the maternal circulation. The elution profile of the IgM found in the foetal sera and in sera from newborn rabbits indicated that this immunoglobulin was in its polymeric form. It was concluded that relatively high concentrations of polymeric IgM are transferred from mother to foetus.