Murine trophoblast can be killed by lymphokine-activated killer cells

The ability of fetal trophoblast cells in the placenta to resist cell-mediated lysis may be important for successful pregnancy. Previous studies in this laboratory demonstrated that cultured midterm mouse trophoblast cells are not susceptible to allospecific CTL generated by standard in vitro protocols, to antibody-dependent cell-mediated cytotoxicity, or to naive or IFN-activated NK cells, despite expressing the requisite target structures. However, we now report that murine trophoblast can be killed, in a non-MHC-specific manner, by LAK cells. Normal mouse spleen cells cultured for 4 days in IL-2-containing lymphokine preparations characteristically killed both NK-sensitive (YAC-1) and NK-resistant (EL4, P815) target cells, and mediated significant lysis of both cultured and freshly isolated trophoblast cells (35 to 55%, E/T 100/1). Pretreatment of the LAK cells with anti-ASGM1 antibody and C markedly reduced the lysis of trophoblast and YAC-1 targets, suggesting that the responsible cells belonged to the NK lineage. The ability of IL-2-activated NK cells to kill midterm murine trophoblast cells was confirmed using a population of highly lytic NK cells generated by culturing spleen cells from severe combined immunodeficiency mice in 500 U/ml rIL-2 for 5 days. These effector cells killed YAC-1, EL4 and P815 target cells at much lower E/T ratios than was achieved with the normal splenic LAK cells, and mediated significant lysis of both freshly isolated (45 to 50%, E/T 20/1) and cultured trophoblast cells (68 to 76%, E/T 20/1). The susceptibility of trophoblast to LAK cells and IL-2-activated NK cells supports the need for suppressor mechanisms regulating IL-2 activity at the maternal-fetal interface.