Figure 4.

Row A depicts low power histological images of uterus and implantation sites in B6 mice stained with H & E, to provide orientation. The mesometrial triangle (M), where development of the mesometrial lymphoid aggregate of pregnancy (MLAp) occurs, is uppermost in all panels. The antimesometrial (AM) side of the uterus is at the bottom of all images. At gestation day (gd) 3, decidualization has yet to commence. At gd 6, maternal decidual tissue (D) fills the uterus, with the embryo at the primitive streak stage occupying the embryonic crypt (EC). By gd 10, there is a fully developed implantation site. The microdomains of the MLAp and decidua basalis (DB) are maternal in origin while that of the placental trophoblast (P) is fetally-derived. Antimesometrial decidua has regressed as the fetus (F) has developed and grown. Rows B and C show low and high power images, respectively, of toluidine blue stained human lymphocytes (some marked by arrows) adhering to 12 μm cryostat sections of mouse uterus at the indicated stages. Binding to decidualized uteri occurred only in the DB. Lymphocyte clustering was prominent at gd 10. Lymphocytes binding to non-decidualized uteri (i.e., gd 3) were dispersed as single cells (70% small, 30% large) with random distribution in the virgin uterus. The most frequently bound cells at gd 3 were dispersed, typical small lymphocytes (85%, black arrowheads) while 15% of bound cells were larger (white arrowheads). As gestation progressed to gd 6, adhesion became restricted to DB, the proportion of large cells declined to 1%, numbers of adherent cells increased and some appeared as stable clustersof up to 30 cells. The clusters were much larger at gd 10 than at gd 6, but the proportion of large adherent cells remained low (3%). Row B Bar = 150 μm, Row C Bar = 40 μm.