TRANSPORT OF IMMUNOGLOBULIN-G AND ITS SUBCLASSES ACROSS THE IN-VITRO PERFUSED HUMAN PLACENTA

OBJECTIVE: The transport of immunoglobulin G and its subclasses 1 to 4 was investigated in the in vitro-perfused isolated cotyledon of the h uman placenta. STUDY DESIGN: An in vitro system with separate perfusio n of the villous capillary system (fetal compartment) and the correspo nding intervillous space (maternal compartment) was set up in an isola ted cotyledon of human term placenta. After a 2-hour control phase wit h both compartments perfused in a closed circuit with NCTC-135 tissue culture medium together with Earl's balanced salt solution (2:1), medi a were exchanged in both circuits and for the experimental phase immun oglobulin G (Sandoglobulin) together with carbon 14-labeled bovine ser um albumin (5-10 mu Ci) was added to the maternal compartment at a con centration of 6 gm/L. During the experimental phase, lasting between 2 and 5 hours, samples were taken from the maternal and fetal compartme nts every 30 minutes up to 2 hours and every 60 minutes thereafter. RE SULTS: During the control phase immunoglobulin G appeared in the mater nal perfusate and reached a plateau at 60 to 80 mg/L, whereas the conc entration in the fetal perfusate did not exceed 20 mg/L. A similar pat tern of release was observed for hemoglobin, suggesting a washout of r emains of blood from the intervillous space and the villous vascular c ompartment. After addition of immunoglobulin G to the maternal circuit during the first 2 hours in three of four experiments, no change in i mmunoglobulin G concentration was seen in the fetal circuit, and only in the fourth and fifth hours did the fetal concentration increase to 0.6% of the maternal concentration. In contrast, carbon 14-labeled bov ine serum albumin was already detectable in the fetal circuit after 1 hour, but the level remained constant at 0.1% of the maternal concentr ation. Total immunoglobulin G transfer was estimated at 0.5% of the am ount added to the maternal circulation, which was five times higher th an total transfer of bovine serum albumin. Transfer was shown for all four subclasses. At the end of the experiment the ratio of immunoglobu lin G(1) to immunoglobulin G(2) in the fetal perfusate was significant ly higher than in the maternal perfusate (3.8 vs 1.8), suggesting pref erential transfer of immunoglobin G(1). CONCLUSION: Transfer of all fo ur immunoglobulin G subclasses of a commercially available immunoglobu lin G preparation across the human placenta from the maternal to the f etal side was demonstrated by the dual in vitro perfusion system. Ther e is a preferential transfer for immunoglobulin G(1).