Malignant potential, major histocompatibility complex antigen expression, and genomic imprinting of rat trophoblast cell lines.

Invasive growth, variation in major histocompatibility complex antigen expression, and genomic imprinting are important properties of both trophoblast cells and malignant tumors. This study, undertaken to address these three issues, used cultured trophoblast cell lines derived from Day 11/12 rat placentas of all mating combinations of the DA and WF inbred strains. In addition, genomic imprinting was also examined in intact rat placentas from Days 11-19. There was no correlation in trophoblast cells between class I antigen expression, DNA content, and cell ploidy on the one hand and oncogenic potential on the other hand. The constitutive suppression of class II antigens in the trophoblast cells could not be abrogated by treatment with interferon-gamma, whereas such treatment always maximally induced class I antigen expression regardless of the initial resting levels. The trophoblast cells at Day 11/12 expressed both maternal and paternal class I antigens, and studies in whole placental tissues showed that the imprinting of the maternal class I antigens was manifested by a decreased level of expression rather than an absence of expression. Thus, genomic imprinting in the rat placenta is a quantitative, rather than an all-or-none, phenomenon.