At Last the Explanation for Increased Spontaneous Miscarriages in Thyroid Autoantibody Positive Pregnant Women

In women who are pregnant, the presence of thyroid autoantibodies is associated with an increased rate of miscarriage in the first trimester, with multiple reports averaging ~17% compared with ~8% in autoantibody negative women. During pregnancy immune tolerance is altered to allow implantation of the semi-allogeneic fetus and T-regulatory cells (Tregs), which play a major role in such tolerance, have been shown to increase during pregnancy, reaching a peak in the second trimester. A deficiency in this Treg response has been widely associated with spontaneous miscarriages. While it is known that the number of Tregs in patients with autoimmune thyroid disease (AITD) is decreased there are no data on pregnant women with AITD. In this study, we examined both the number and function of Tregs in pregnant women with (n=26) and without (n=41) thyroid autoantibodies (anti-Tg and/or anti-TPO) as well as healthy non pregnant women (n=25). Tregs were measured by flow cytometry of isolated CD4+, CD25+ and FoxP3+ T-cells. We found that the total number of CD4+CD25+FoxP3+ (high) Tregs was significantly increased in pregnancy consistent with previous reports (from 11% to 22%, p<0.024). Furthermore, this increase in Tregs was less in pregnant women with thyroid autoantibodies (mean of 12%). In addition, studies of phosphorylated signal transducer and activator of transcription-5a (pStat-5a) as a marker of Treg function, showed that while Tregs were activated in pregnancy, their activity per cell was diminished in the pregnant antibody positive women with a frequency:MFI ratio of 201 compared to 316 in the negative group. These data demonstrate that pregnant women with thyroid antibodies have a reduced Treg response to pregnancy, both in number and function, and offer a likely explanation for the increased miscarriage rate in such patients.