Introduction Pregnancy is associated with a heightened susceptibility to many pathogens and with more severe clinical symptoms. The only preventive treatment currently available is vaccine, but the breadth of potential coverage is limited by vaccine availability. To circumvent this limitation, we were interested by a new class of treatment: the immunostimulation. Immunostimulation has been previously shown to limit infection severity, but it has never been tested during pregnancy. As a proof-of-principle, we investigated the efficacy of a prophylactic treatment with an immunostimulant (OM-85) to protect from Influenza infection in a mouse model.
Methods BALB/c mice were time-mated and fed OM-85 once a day from gestational day (GD) 0.5. Mice were infected with a low dose of H1N1 influenza A virus (mouse adapted PR8 strain) at GD9.5 (corresponding to mid-late gestation). Disease severity was assessed daily and the immune response was assessed by flow cytometry in the airway and gestation tissues.
Results Prophylactic treatment with OM-85 attenuates the severity of Influenza infection in pregnant mice, as shown by reduced viral load and reduced maternal weight loss. In addition, fetal growth retardation induced by Influenza was diminished by prophylactic immunostimulation. Influenza infection was associated with an increased accumulation inflammatory cells, including inflammatory dendritic cells, activated T cells and granulocytes, in both the airways and the gestational tissues. Interestingly, OM-85 treatment was able to reduce the inflammatory response to Influenza.
Conclusions Overall, we showed that OM-85 treatment prevent influenza-induced pregnancy complications by reducing inflammatory cell recruitment in the airway and gestational tissues.