Natural cytotoxicity in the mouse embryo: characterization of yolk sac-associated natural cytotoxic cells and their activity.

Abstract

The natural cytotoxic activity of yolk sac (YS) cells from 10-day mouse embryos against YAC-1 tumor targets was characterized for its sensitivity to modulation by a variety of factors. Experiments demonstrated the observed levels of tumor cell lysis to be unaffected by the strain of origin of the YS cells, trypsin pretreatment of the YS population, as well as a prior stimulation by environmental pathogens. Both the YS natural cytotoxic (YSNC) activity and the adult natural killer (NK) cell activity were found to be depressed when assayed in the presence of amniotic fluid. YS cells were tested for antibody-dependent cell-mediated cytotoxic activity, but were not found to generate significant levels of lysis. Experiments presented here demonstrate the YSNC activity to be dependent upon only a subpopulation of YS cells. The YSNC activity was found to be associated only with the cells exhibiting high forward angle light scatter as determined by flow cytometry. Additionally the activity was unaffected by the removal of plastic-adherent cells from the effector population. In this study, YSNC cells are also examined for the presence of a variety of lymphocyte antigens. The effector cells, as well as the total YS population, were found to lack Lyt-1, Lyt-2, Thy-1, Ly-5, NK-1, Qa-5, asialo GM1, and H-2 antigens. While these experiments demonstrate the YSNC cells to be distinct from the NK cells of the adult, they do not rule out a potential common lineage for the two natural cytotoxic cell types.