Abstract

Influenza A virus infection during pregnancy can cause adverse maternal and fetal outcomes, but the mechanism responsible remains elusive. Infection of outbred mice with 2009 H1N1 at embryonic day (E) 10 resulted in significant maternal morbidity, placental tissue damage and inflammation, fetal growth restriction, and developmental delays that lasted through weaning. Restriction of pulmonary virus replication was not inhibited during pregnancy, but infected dams had suppressed circulating and placental progesterone (P4) concentrations that were caused by H1N1-induced upregulation of pulmonary cyclooxygenase (COX)-1, but not COX-2-, dependent synthesis and secretion of prostaglandin (PG) F2. Treatment with 17--hydroxyprogesterone caproate (17-OHPC), a synthetic progestin that is safe to use in pregnancy, ameliorated the adverse maternal and fetal outcomes from H1N1 infection and prevented placental cell death and inflammation. These findings highlight the therapeutic potential of progestin treatments for influenza during pregnancy. ImportancePregnant individuals are at risk of severe outcomes from both seasonal and pandemic influenza A viruses. Influenza infection during pregnancy is associated with adverse fetal outcomes at birth and adverse consequences for offspring into adulthood. We developed an outbred mouse model of 2009 H1N1 influenza virus infection during pregnancy, with semi-allogenic fetuses. When dams are infected with 2009 H1N1, in addition to pulmonary virus replication, tissue damage, and inflammation, the placenta shows evidence of transient damage and inflammation that is mediated by increased activity along the arachidonic acid pathway leading to suppression of circulating progesterone. Placental damage and suppressed progesterone are associated with long-term effects on perinatal growth and developmental delays in offspring. Treatment of H1N1-infected pregnant mice with 17-OHPC, a synthetic progestin treatment safe that is safe to use in pregnancy, prevents placental damage and inflammation and adverse fetal outcomes. This provided a novel therapeutic option for treatment of influenza during pregnancy that should be explored clinically.