Experimental Antigen Modulation of Blastocysts for Mimicing Dormant and Invasive Micrometastases

The mouse preimplantation period can be prolonged experimentally by a delayed implantation, and this will keep the blastocyst in an inactive state. The dormancy can be interrupted by an oestrogen injection, which will make the blastocyst invasive. Thus the blastocyst mimics both dormant and invasive micrometastasis. Considering the similarities between blastocysts and micrometastases in cellular activation, we have developed methods for examining antigen modulations using the blastocyst as a model. Evaluating the total amount of antibody in the blastocyst and also the trophoblast antigen synthesis, shedding, and endocytosis, we found that dormant cells exposed to a surface-specific antibody kept the immune complexes on the cell surface for a longer time than did the invasive cells. The rate of internalization of immune complexes was low in both dormant and invasive cells, but since the shedding activity was less active in the dormant cells they contained more antibodies totally than did the invasive ones under the same conditions. When exposing the cells to an anti-cytoplamic antibody or to non-specific antibodies, the amount of antibodies in the cytoplasm of invasive cells was higher than in dormant cells. The methods used for examining the antigen modulation by the blastocyst should be useful also for studying the handling of antibodies by micrometastases.