Bone marrow (BM) harbors precursors (Pre-NK) to NK cells. Recently, we devised an in vitro culture system that induces differentiation of the presumptive BM Pre-NK cells into cytotoxic cells to YAC in the presence of rat concanavalin A (Con A) conditioned medium. We have now analyzed the antigenic phenotype of the effector cells, precursor cells, and the target specificity of these cytotoxic cells. The cytotoxic cells had antigenic profiles similar to endogenous NK cells with the exception of Lyt-2 antigen. They are strongly positive for Qa-5, Thy-1, and partially positive for NK-1, Ly-5, Ly-6, Ly-10, and AsGm-1 and Lyt-2 antigens. The Pre-NK or accessory cells are positive for Qa-5, Ly-10, and Ly-20 and partially positive for NK-1, Thy-1, and AsGm-1 antigens. These Qa-5+ NK cells do not exhibit cytotoxic activity to WEHI or P815. They could also be generated from BM of nude mice as well as beige mice. We concluded from these studies that rat Con A-conditioned medium contained factors that could differentiate Pre-NK cells to mature NK cells and that these cells are heterogeneous. This in vitro culture system is useful in delineating the ontogeny of NK cells.
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