Elevated Serum Level of IL-35 Associated with the Maintenance of Maternal-Fetal Immune Tolerance in Normal Pregnancy

OBJECTIVES: IL-35 is a novel inhibitory cytokine. In this study, we investigate the serum levels of inhibitory cytokines IL-35, IL-10 and TGF-β in both normal pregnancies and non-pregnant females, and whether IL-35 is associated with the pathogenesis of recurrent spontaneous abortion. We also try to elucidate the relationships of IL-35 with estrogen and alpha-fetoprotein (AFP). METHODS: The levels of IL-35, IL-10, TGF-β, estradiol (E2), unconjugated estriol (uE3) and AFP were analyzed in 120 normal pregnancies, 40 women suffering recurrent spontaneous abortion, 40 postpartum healthy women and 40 non-pregnant women by enzyme-linked immunosorbent assay (ELISA). The correlations between inhibitory cytokines, estrogen and AFP were assessed with the Spearman rank correlation coefficient. RESULTS: Data are expressed as median and percentiles (Q1, Q3).The level of serum IL-35 in normal pregnancies was significantly higher than that in non-pregnant women [333.6 (59.32, 1391) pg/mL vs. 123.9 (8.763, 471.7) pg/mL; P < 0.001]. A significantly higher level of TGF-β was observed in the first trimester only as compared to non-pregnant women [473.4 (398.0, 580.5) pg/mL vs. 379.7 (311.0, 441.3) pg/mL, P < 0.01]. The difference in serum IL-10 level between pregnant women and non-pregnant women was not significant [8.602 (5.854, 12.89) pg/mL vs. 9.339 (5.691, 12.07) pg/mL; P > 0.05]. The level of serum IL-35 in recurrent spontaneous abortion was significantly lower than that in normal early pregnancy [220.4 (4.951, 702.0) pg/mL vs. 386.5 (64.37, 1355) pg/mL; P < 0.05]. The higher IL-35 level in first trimester pregnant women correlated with E2 (r = 0.3062, P < 0.01) and AFP (r = 0.3179, P < 0.01). CONCLUSION: Serum levels of IL-35 increased in normal pregnancy and decreased in recurrent spontaneous abortion. Increased IL-35 correlated with estrogen and AFP levels in early pregnancy. IL-35 is becoming recognized as an active player in the maintenance of a successful pregnancy, but this is not the case for IL-10 or TGF-β.