Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

A conspicuous feature of human placentation is the invasion of uterine tissue by large numbers of fetal extravillous trophoblast cells (EVT) which infiltrate the decidua to reach as far as the superficial layer of the myometrium (Pijnenborg et al., 1981; Loke and Butterworth., 1987). Trophoblast cells also become incorporated into the walls of the spiral arteries, as part of an decidual invasion per se which converts the vessels into sinusoidal sacs. These changes are thought to be important for the establishment of the low resistance blood supply to the developing placenta (Robertson., 1987). Interstitial trophoblast cells are a sub-population of the EVT which infiltrates the maternal uterine tissue at the implantation site. In the early literature, these trophoblast cells were referred to variably as X-cells (Wynn., 1972) or as "intermediate" trophoblast cells with characteristic morphological and biochemical features (Kurman et al., 1984a). The mechanisms which govern this extensive trophoblast migration are not fully understood. The maternal tissue underlying the implantation site is known as the decidua basalis, and is composed of various cell types. Among the maternal cells which are found intermingled with the fetal interstitial trophoblast cells are CD56 positive natural killer cells (Uren and Boyle., 1985; King and Loke., 1990; King et al., 1991; Mincheva-Nilsson et al., 1994) and macrophages (Bulmer and Johnson., 1984; Bulmer et al., 1988; Hunt., 1989; Hunt et al., 1990) whose morphology has been well characterised. Numerous investigations have suggested that a suitable balance must be maintained between the maternal and fetal cells if proper placentation is to occur. In this study we report that the first trimester human interstitial trophoblast cells can be clearly separated into two populations, type I electron-lucent agranular and type II electron-dense granular using ultrastructural and immunocytochemical criteria.

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