Serum heat shock protein 70 levels are decreased in normal human pregnancy.

Heat shock proteins (Hsps) are primarily known to be intracellular proteins with molecular chaperone and cytoprotective functions. However, Hsp60 and Hsp70 have been found in the serum and plasma of healthy non-pregnant individuals. We aimed to compare serum Hsp70 concentrations in healthy pregnant women with those of healthy non-pregnant women and to determine factors influencing serum Hsp70 levels in normal pregnancy. One hundred and seventy six healthy pregnant women with uncomplicated pregnancies (age, 17-44 years; gestational age, 20-41 weeks) and 81 healthy, age-matched non-pregnant women (age, 22-40 years) were enrolled in this cross-sectional study. Serum Hsp70 concentrations were measured using an enzyme-linked immunosorbent assay, and were significantly lower in healthy pregnant women than in healthy non-pregnant women (median (25-75 percentile): 0.29 (0.20-0.35)ng/ml versus 1.27 (0.86-1.72)ng/ml; p<0.001). In healthy pregnant women, there was a statistically significant negative correlation between maternal age and serum Hsp70 concentration (Spearman R=-0.35; p<0.001) and a significant positive correlation between gestational age and serum Hsp70 level (Spearman R=0.35; p<0.001). The capacity of extracellular Hsp70 to elicit innate and adaptive proinflammatory immune responses might be harmful in pregnancy and lead to immune rejection of the fetal semi-allograft. We hypothesize that decreased circulating Hsp70 levels are due to unknown regulatory mechanisms aimed at maintaining immune tolerance in pregnancy. In conclusion, serum Hsp70 concentrations are decreased in normal human pregnancy; however, further studies are needed to explain the observed differences between pregnant and non-pregnant women.