No abstract

The fetoplacental unit resulting from an allogeneic mating is a natural allograft that is not rejected by the otherwise immunocompetent mother (1, 2). Of the various hypotheses proposed to explain this phenomenon, the possible absence of major histocompatibility antigens from the surface of the fetally derived trophoblast cells which lie at the fetomaternal interface has been the focus of extensive investigation (3)(4)(5)(6)(7)(8)(9)(10)(11).We have recently demonstrated (10) the presence of H-2K and D antigens of both maternal and paternal haplotypes on the surface of murine trophoblast cells in suspensions of collagenase-dispersed placentae from 9 to 18 d of gestation, using monospecific antisera and a highly sensitive radioautographic technique. The antigen density on 19-and 14-d trophoblasts was comparable to that on adult F1 thymocytes and a further 50% increase was observed at term. However, the question still remained as to whether these antigens are expressed in situ, and if so, whether they are detectable on the face of trophoblast cells that line the maternal sinusoids in vivo, and thus accessible to the maternal circulation. Studies by Kirby and Cowell (11) and Parr et al. (12) have demonstrated that H-2 antigens may be sequestered on one aspect of certain cells, e.g., the epithelial cells of the small intestine and the endoderm cells of the yolk sac.This study was designed to examine the presence of H-2K antigens on the sinusoidal surface of murine trophoblast cells in vivo, without destroying the architecture of the intact placenta. The use of a radioautographic technique, after an in vivo perfusion with radioiodinated antibodies via individual placental branches of the uterine artery, ensured high levels of sensitivity. High levels of specificity were provided by the use of monoclonal antibodies raised against the H-2K antigens of the paternal haplotype. The visualization and quantitation of radioautographic silver grains on morphologically identified trophoblast cells allowed good resolution. The results revealed significant levels of H-2K antigens of the paternal haplotype on the sinusoidal face of mouse trophoblast cells in the labyrinthine region of placentae derived from allogeneic matings. Materials and MethodsMice. C57BL/6J females were mated with CBA/J or C57BL/6J males (6-12 wk of age; The Jackson Laboratory, Bar Harbor, ME) and provided allogeneic and syngeneic placentae,

The presence of H-2 antigens of the paternal and maternal haplotypes on mouse trophoblast cells was examined at several stages of pregnancy by using a sensitive immunolabeling technique followed by quantitative radioautography. Results revealed the presence of H-2 antigens (determined by the K or D loci) of both parental haplotypes on the F1 trophoblast cells. At 14-16 d of gestation, the antigen density was equivalent to that on adult thymocytes and there was a further 50% increase on day 18. H-2 antigens of both parental haplotypes are also found to be expressed on 11-13 d trophoblast cells.