Placental transfer of IgG subclasses in a Japanese population

Background: Maternal immunoglobulin G (IgG), transferred across the placent a to the fetus during intrauterine life, is an important component of the n eonatal immunological defence mechanisms against infection. There is contro versy with respect to differences in placental transfer of the different Ig G subclasses, and no definite data are available on a Japanese population. Therefore, we investigated placental transfer of IgG subclasses in a Japane se population. Methods: A total of 228 matched pairs of cord and maternal serum samples (2 0-42 weeks gestation) were assayed for each IgG subclass by an enzyme-linke d immunosorbent assay. Results: The mean values and hierarchy of cord/maternal concentration ratio s of IgG subclasses at 40 weeks gestation were as follows: IgGl(1.47)> IgG3 (1.17)=IgG4(1.15)> IgG2(0.80). The cord/maternal concentration ratios of al l IgG subclasses were positively correlated to gestational age. The mean ra tios for IgG1 and IgG4 nearly reached a plateau at 39 and 37 weeks gestatio n, respectively, while those for IgG2 and IgG3 increased until 41 weeks ges tation. The ratios of all IgG subclasses for full-term deliveries were reci procally correlated to the respective maternal IgG subclass serum levels. Conclusions: The results suggest that although all four IgG subclasses are actively transferred across the placenta, the efficiency of their transfer ranks in the order IgGl > IgG3=IgG4 > IgG2. The different results as to pla cental transfer of IgG subclasses in the literature might be due, at least in part, to different maternal IgG subclass serum levels in the populations studied.