Embryo infiltration by maternal macrophages is associated with selective expression of proto-oncogenes in a murine model of spontaneous abortion.

The causes and precise mechanisms leading to early embryo loss in mammals remain largely unknown, especially from a molecular point of view. Using the CBA/J x DBA/2 murine model of early spontaneous embryo loss (25-30% embryo loss), we have previously demonstrated the involvement of infiltrating activated macrophages and their cytolytic products such as nitric oxide and tumor necrosis factor alpha (TNF alpha) in the etiology of early embryo loss. On the other hand, far fewer of the CBA/J x Balb/c conceptuses (5-10% embryo loss) displayed significant cellular infiltration and nitric oxide and TNF alpha. Having used probes for cellular activation markers, we now present evidence indicating that significantly increased expression of AP-1 family members, Ha-ras, Ki-ras, v-erbA, v-raf, v-abl, and c-myc was present in 24.4% of the CBA/J x DBA/2 embryonic units that also harbored significant Mac-1, F4/80, and class II major histocompatibility complex (MHC) molecule cellular infiltration. In contrast, only 7% of CBA/J x Balb/c conceptuses displayed increased proto-oncogene expression and increased cellular infiltration. Therefore, macrophage infiltration, cellular activation as identified by the increased expression of proto-oncogenes, and the production of cytotoxic macrophage products are closely linked to early embryo loss. These data add to the evidence that activated maternal macrophages may be directly responsible for spontaneous pregnancy failure.