The success of eutherian mammal evolution was certainly supported by the ability of the already existing immune system to adapt to the presence of the semi-allogeneic fetus without losing the capability to defend the mother against infections. This required the acquisition of highly regulated and coordinated immunological mechanisms. Failures in the development of these strategies not only lead to the interruption of pregnancy but also compromise maternal health. Alongside changes on the cytokine profile – expansion of tolerogenic dendritic and regulatory T cells – a profound adaptation of the B cell compartment during pregnancy was recently described. Among others, the suppression of B cell lymphopoiesis and B cell lymphopenia were proposed to be protective mechanisms tending to reduce the occurrence of autoreactive B cells that might recognize fetal structures and put pregnancy on risk. On the other hand, expansion of the pre-activated marginal zone (MZ) B cell phenotype was described as a compensatory strategy launched to overcome B cell lymphopenia thus ensuring a proper defense. In this work, using an animal model of pregnancy disturbances, we demonstrated that the suppression of B cell lymphopoiesis as well as splenic B cell lymphopenia occur independently of pregnancy outcome. However, only animals undergoing normal pregnancies, but not those suffering from pregnancy disturbances, could induce an expansion and activation of the MZ B cells. Hence, our results clearly show that MZ B cells, probably due to the production of natural protective antibodies, participate in the fine balance of immune activation required for pregnancy well-being.
Damián O Muzzio, Katharina B Ziegler, Jens Ehrhardt, Marek Zygmunt and Federico Jensen
Imke Bommer, Lorena Juriol, Damián Muzzio, Natalin Valeff, Jens Ehrhardt, Franziska Matzner, Katharina Ziegler, Kristin Malinowsky, María Silvia Ventimiglia, Marek Zygmunt and Federico Jensen
The amniotic fluid provides mechanical protection and immune defense against pathogens to the fetus. Indeed, components of the innate and adaptive immunity, including B cells, have been described in the amniotic fluid. However, limited information concerning phenotype and functionality of amniotic fluid B cells is available. Hence, we aimed to perform a full phenotypical and functional characterization of amniotic fluid B cells in normal pregnancy and in a mouse model of preterm birth. Phenotypic analysis depicted the presence of two populations of amniotic fluid B cells: an immature population, resembling B1 progenitor cells and a more mature population. Further isolation and in vitro co-culture with a bone marrow stroma cell line demonstrated the capacity of the immature B cells to mature. This was further supported by spontaneous production of IgM, a feature of the B1 B cell sub-population. An additional in vitro stimulation with lipopolysaccharide induced the activation of amniotic fluid B cells as well as the production of pro and anti-inflammatory cytokines. Furthermore, amniotic fluid B cells were expanded in the acute phase of LPS-induced preterm birth. Overall our data add new insight not only on the phenotype and developmental stage of the amniotic fluid B1 B cells but especially on their functionality. This provides important information for a better understanding of their role within the amniotic fluid as immunological protective barrier, especially with regard to intraamniotic infection and preterm birth.