Complement activation in postpartum thyroiditis

Postpartum thyroid dysfunction (PPTD) develops in 50% of pregnant women who have raised levels of circulating thyroid peroxidase autoantibodies (TPOAb) at booking. Although these antibodies are able to activate the complement cascade in vitro, it is not known whether complement activation plays any role in the pathogenesis of this disease.

To investigate potential and actual activation of the complement system in women with postpartum thyroiditis.

Complement activation was monitored on a weekly basis in 24 postpartum women who had raised TPOAb at 16 weeks gestation, attending an antenatal clinic in Mid-Glamorgan, Wales.

ELISA procedures were used to measure both in-vitro complement C3 activation by TPOAb and circulating terminal complement complexes (TCC) in serum.

Higher levels of bioactive TPOAb activity were seen in women who developed PPTD when compared to those who did not. However, TCC remained undetectable in serum throughout the period of study.

In PPTD, despite the presence of circulating bioactive TPOAbs, the extent of complement activation is inadequate to cause detectable increases in peripheral blood TCC, suggesting that the complement system may not play a major role in PPTD pathogenesis.