Transgenic Major Histocompatibility Complex Class I Antigen Expressed in Mouse Trophoblast Affects Maternal Immature B Cells1

We have produced transgenic mice using the mouse placen-tal lactogen type II promoter to force and restrict the expression of the mouse major histocompatibility complex (MHC) class I molecule, H-2Kb, to the placenta. We show that the transgenic MHC antigen H-2Kb is expressed exclusively in trophoblast giant cells from Day 10.5 until the end of gestation. This expression affects neither the fetal development nor the maternal tolerance to the fetus in histoincompatible mothers. We have used the 3.83 B cell receptor (BcR) transgenic mouse line to follow the fate of H-2Kb-specific maternal B cells in mothers bearing H-2Kb-positive placentas. Our results suggest that transgenic H-2Kb molecules on trophoblast giant cells are recognized by 3.83 BcR-transgenic B cells in the bone marrow of pregnant females. This antigen recognition triggers the deletion of a bone marrow B cell subpopulation, including immature and transitional B cells. Their percentage decreases during the second half of ges-tation and is down to 8 % on Day 17.5, compared to 22 % in the (3.83 Tg female 3 Fvb) control group. This deletion might contribute to the process of maternal tolerance of the concep-tus. developmental biology, embryo, gene regulation, immunology, placenta, pregnancy, trophoblas