Maternal immunoglobulins G, A and M in mouse uterus and embryo during the postimplantation period

The distribution of maternal IgG, IgA and IgM was studied by an immunoperoxidase technique on mouse uteri and embryo sections from 4.5 to 10 days of gestation. In the embryo, from day 5, IgG was found in the endoderm, and later in the trophoblast, distal and extraembryonic proximal endoderm, embryo cavity and early vitelline vessels. From day 6, IgA was found in the same areas but staining was less intense and was not seen in vitelline vessels. From day 8, small amounts of IgM were found in the same areas, but not in vitelline vessels. Between implantation sites, IgG and plasma cells containing IgA remained present in the stroma; most glands contained IgA, and the uterine lumen stained for IgA and IgG. IgG granules were found in the apical region of luminal epithelial cells in the implantation sites at 5 and 5.5 days; IgA granules were seen in the apical region of luminal epithelial cells between implantation sites from 4.5 to 6.5 days. These results suggest that IgA and some IgM are transmitted along with IgG to the early mouse embryo but do not reach the embryonic circulation, and that during the implantation period reabsorption of IgG and IgA from the uterine lumen into the epithelium differs, depending on the position of this epithelium in relation to the embryo. The persistent IgA and IgG secretion in the uterus after implantation suggests that during this period the mechanisms regulating immunoglobulin secretion may differ from those during the oestrous cycle.