An update on anti-protein Z antibodies

Protein Z (PZ) is a vitamin K-dependent protein that acts as a cofactor for the inhibition of activated factor X by the PZ-dependent protease inhibitor, an anticoagulant protein of the serpin superfamily. The presence of antibodies against PZ (aPZ-Abs) was first described in women with unexplained recurrent embryo loss, pre-eclampsia, or foetal death, independently from habitual antiphospholipid/anti-cofactor antibodies. Other studies suggested that aPZ-Ab could be associated with a small birthweight for the gestational age. The mechanism of action of these antibodies is not yet understood. At this time, even aPZ-Abs are frequently observed in patients with lupus anticoagulant or anticardiolipin antibodies, there is no evidence that aPZ-Abs increase systemic venous or arterial thrombotic risk. The comparison of the various published studies shows that the threshold suggesting an obstetric risk is not clearly defined. At present, it is not known whether one isotype of immunoglobulin (G or M, or both) is particularly involved in certain obstetric manifestations, or these antibodies persist during time, or can be induced by infectious diseases. Consequently, detection of these antibodies is not routinely warranted and should only be performed in randomized clinical trials.