[The concentration of fetal cells in maternal haematopoietic organs during pregnancy. An experimental study in mice (author's transl)].

We have been able to show that fetal cells are able to survive and multiply in the haematopoietic organs of the pregnant mouse. We have been able to label fetal cells with a chromosome marker (T6) which is clearly visible in the metaphase of mitosis. It is not only that there is a considerable concentration of fetal cells in the maternal spleen (3 to 6 per cent) but there are several factors that suggest that these fetal cells can multiply there. These are, the presence of mitoses, long survival, and a rise in numbers in the case of a new pregnancy. Thus pregnancy seems to bring about a physiological "microchimerism".