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For the normal development of pregnancy, a balance between immune tolerance and defense is crucial. However, the mechanisms mediating such a balance are not fully understood. CD83 is a transmembrane protein whose expression has been linked to anti-inflammatory functions of T and B cells. The soluble form of CD83, released by cleavage of the membrane-bound protein, has strong anti-inflammatory properties and was successfully tested in different mouse models. It is assumed that this molecule contributes to the establishment of immune tolerance. Therefore, we postulated that the expression of CD83 is crucial for immune tolerance during pregnancy in mice. Here, we demonstrated that the membrane-bound form of CD83 was upregulated in T and B cells during allogeneic murine pregnancies. An upregulation was also evident in the main splenic B cell subtypes: marginal zone, follicular zone, and transitional B cells. We also showed that there was an augmentation in the number of CD83+ cells toward the end of pregnancy within splenic B and CD4+ T cells, while CD83+ dendritic cells were reduced in spleen and inguinal lymph nodes of pregnant mice. Additionally, B lymphocytes in late-pregnancy presented a markedly higher sensitivity to LPS in terms of CD83 expression and sCD83 release. Progesterone induced a dosis-dependent upregulation of CD83 on T cells. Our data suggest that the regulation of CD83 expression represents a novel pathway of fetal tolerance and protection against inflammatory threats during pregnancy.
Introduction:
The amniotic fluid – as the medium surrounding the fetus, it is holding a crucial role in the maintenance and development of a successful pregnancy. While providing mechanical protection to the fetus, it also offers considerable immunological defense. In fact, it is known that the amniotic fluid plays a significant role in the innate immune system, as many of its corresponding substances show substantial antimicrobial function. Also, components of the adaptive immune system, including B cells, have been described within the amniotic fluid. An increase of immune cells in the amniotic fluid in cases of intra-amniotic infection indicates their involvement in inflammation-related pathologies of pregnancy. However, especially B cells in the amniotic fluid have not yet been thoroughly investigated.
The aim of this work is a deeper examination of the B-lymphocytes within the amniotic fluid. Based on the analysis of surface molecules this includes their phenotype, origin and func-tion. In the long term this could substantiate our understanding of intraamniotic inflammation and or infection, which are casually linked with preterm birth, fetal inflammatory response syndrome and fetal morbidity.
This, in turn, could pave the way for potential diagnostic methods and treatments.
Methods:
For all experiments 8-12-weeks-old pregnant mice were sacrificed at day 14 of pregnancy. The amniotic fluid was collected and specific cell subsets were isolated using MACS cell separation. Cells were then co-cultured with a bone marrow stromal cell line and stimulated in vitro.
The analysis of the population distribution and cytokine production was performed by flow cytometry. To analyze IgM-levels in the supernatant of the co culture, ELISA was used. Statistical analysis was performed using GraphPad Prism software.
Results:
The amniotic fluid contains different developmental stages of B cells, which most likely are of fetal origin. This is supported by the expression of paternal surface markers. An extensive proliferation and switch towards a more mature phenotype upon co-culture shows that the immature subsets of amniotic fluid B cells are able to expand and mature in vitro. Amniotic
fluid B cells spontaneously produce IgM and show functional adaption upon in vitro stimula-tion as evidenced by the increase of cell activation markers.
Conclusion:
For the first time a deep investigation of B-cells within the amniotic fluid was performed, covering phenotype and cell functionality. This work shows that there is a B cell compartment within the amniotic fluid, which, to a certain extent, is able to mature and gain functionality when exposed to external stimuli. This supports the hypothesis of the amniotic fluid as crucial immunological line of defense against inflammatory and infectious challenges during pregnancy.
During pregnancy, the maternal immune system faces a double dilemma: tolerate the growing semi-allogeneic fetus and at the same time protect the mother and the progeny against pathogens. This requires a fine and extremely regulated equilibrium between immune activation and tolerance. As professional antigen presenting cells, B cells and in particular B-1a B cells, can activate or tolerize T cells and thus participate in the generation or regulation of the immune response. B-1a B cells were involved in the humoral immune response leading to pre-eclampsia, one of the main medical complications during pregnancy. Here we demonstrated that B-1a B cells are additionally involved in cellular immune mechanisms associated with pregnancy complications. Using a mouse model of pregnancy disturbances, we showed that B-1a B cells from animals suffering pregnancy disturbances but not from those developing normal pregnancies induce the differentiation of naïve T cells into Th17 and Th1 cells. This differential role of B-1a B cells during pregnancy seems to be associated with the co-stimulatory molecule CD86 as normal pregnant mice showed lower percentages of CD86 expressing B-1a B cells as compared to pregnant mice developing pregnancy disturbances or to non-pregnant animals. Our data bring to light a new and not explored role of B-1a B cells in the context of pregnancy.
The Role of Pregnancy-Associated Hormones in the Development and Function of Regulatory B Cells
(2014)
During mammalian pregnancy, highly specialized mechanisms of immune tolerance are triggered in order to allow the semi-allogeneic fetus to grow within the maternal uterus in harmony with the maternal immune system. Among other mechanisms, changes in the endocrine status have been proposed to be at least part of the machinery responsible for the induction of immune tolerance during pregnancy. Indeed, pregnancy-associated hormones, estradiol, progesterone, and human chorionic gonadotropin are known to confer immune suppressive capacity to innate as well as adaptive immune cells. Regulatory B cells, a subpopulation of B lymphocytes with strong immunosuppressive functions, were shown to expand during pregnancy. Furthermore, it is well-known that some women suffering from multiple sclerosis, significantly improve their symptoms during pregnancy and this was attributed to the effect of female sex hormones. Accordingly, estradiol protects mice from developing experimental autoimmune encephalomyelitis by triggering the expansion and activation of regulatory B cells. In this review, we discuss different mechanisms associated with the development, activation, and function of regulatory B cells with a special focus on those involving pregnancy-associated hormones.