In rodents, maternal immunoglobulins are transported intact by the yolk-sac visceral epithelium from mother to fetus. The main purpose of the present paper is to study the dynamics of the uptake and transport of immunoglobulins by the rat yolk-sac using a new experimental design. The results show the rapid binding of IgG to the cell membrane microvilli since only 30 sec were sufficient for this attachment to occur. The endocytic process also appears to be very fast as localization of IgG in clusters, pits and microvesicles were observed after 5 min of contact between the yolk-sac and the IgG solution. Moreover, the antibodies were detected in the intracellular spaces within 15 min of incubation.

Recent experiments suggested that alpha‐protein (AFP) may have immunoregulatory properties and play a role in protecting the fetus from rejection by the mother. The present study was performed to determine whether purified human AFP, its molecular variants separated on Lens culinaris agglutinin, and fetal serum albumin showed immunoregulatory activiiy on in vitro transformation of normal human lymphocytes by mitogens or by allogeneic cells. Human AFP and fetal serum albumin were purified from human whole fetuses by immunoabsorption, followed by acid elution. AFP variants (HLI, HL2, HL3, HL4) were separated by lectin affinity chromatography. The proteins were tested in lymphocyte cultures stimulated by concanavalin A, phytohaemagglutinin and pokeweed mitogen and in mixed lymphocyte cultures. Four batches of AFP and one batch of fetal albumin, in the concentration range of 0‐100 μg/ml and in one experiment up to 2 mg/ml, had a stimulatory effect on lymphocytes. One batch of human AFP showed inhibitory effect with low reproducibility. The variants had a stimulatory effect except for HL3, which was found to be slightly inhibitory in phytohaemagglutinin stimulated cultures when compared with cultures without AFP, but there was no significant difference when compared with cultures in which AFP was replaced by its dialysate. Thus, the results reported here are not consistent with the conclusion that human AFP has a significant immunosuppressive effect on man. Hypotheses about causes of discrepancies are analysed.

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