Evolution of Maternofetal Transport of Immunoglobulins During Human Pregnancy

PROBLEM: We determined the evolution of the maternal-fetal transport of immunoglobulins during human pregnancy. METHOD: Paired blood samples were collected between 17–41 weeks of gestation (WG) by puncture of a peripheral maternal vein and by cordocentesis (17–36 WG, n=91) or directly at delivery (37–41 WG, n=16) from the umbilical vein. Additional maternal samples were collected from the same individual (n=16) at 10,20,30 WG, and at term. The concentration of IgG and its four subclasses and of IgA were determined in the sera using ELISA method. RESULTS: The mean level of IgG and IgA in maternal sera at 9–16 WG was 13.72±2.53 g/L and 3.95±1.23 g/L, respectively. Both, IgG and IgA throughout pregnancy decreased to a level of 60–70% (37–41 WG) of the initial concentration in early pregnancy. The ratio of IgG₁:IgG₂ in the maternal circulation was 2–3 and remained constant throughout pregnancy (17–41 WG). IgG₃ and IgG₄ levels remained constant and together were less than 10% of total IgG. In the fetal circulation a continuous rise in the level of both IgG and IgA was observed between 17 and 41 WG. Fetal level of IgG at 17–22 WG was only 5–10% of the maternal level and at term exceeded the maternal level reaching a value of 11.98±2.18 g/L. IgG₁ at 17–22 WG was 0.93±0.42 g/L, which is approximately three times higher than IgG₂. IgG, showed an exponential rise and at 37–41 WG its concentration was seven times higher than IgG₂. IgG₃ and IgG₄ also showed an exponential rise and at term reached a similar level as in the maternal circulation. Striking was the difference in results for IgG₂ with a slow linear rise throughout gestation. The fetal IgG₂ level at term remained significantly below the maternal concentration. The IgG subclasses when characterized according to the differences in transport capacity gave the following sequence: IgG₁>IgG₄>IgG₃>IgG₂. Fetal IgA showed a slow linear rise with fetal levels at term remaining approximately 1,000 times lower than the concentration in the maternal circulation. CONCLUSIONS: Comparison of fetal and maternal levels of Immunglobulines indicate that the human placenta during pregnancy develops a specific transport mechanism for IgG. There are differences for the four subclasses with preferential transfer of IgG₁ while the slowest transfer is seen for IgG₂.