[The natural killer system in the human fetus]

Natural cytotoxic activity of cells from human fetal spleen, liver, bone marrow, appendix, tonsilar glands and thymus was investigated in 14-26-week-old embryos. The spleen and liver expressed powerful NK activity against K-562 target cells from a 22 week-old embryo. Thymocytes and cells from the appendix and tonsilar glands displayed but negligible cytotoxic activity.