Human fetal thymus and bone marrow contain target cells for natural killer cells.

Abstract

AbstractPrevious studies in the mouse natural killer (NK) system have indicated that NK cells may be involved in lysing normal, primary hematopoietic tissues. In the present report, this was analyzed in the human NK system using fetal bone marrow (BM) cells and thymocytes as well as adult BM cells from healthy donors as target cells in a conventional 6 to 12‐h 51Cr‐release assay.Adult BM cells showed low but significant levels of sensitivity, which could be increased by using interferon (IFN)‐activated peripheral blood leukocytes (PBL) as effector cells. BM cells from 16 to 19‐week‐old fetuses consistently showed higher sensitivity for lysis than adult BM, and also fetal thymocytes proved very sensitive for lysis, in contrast to what has previously been reported for adult thymocytes. When used as effector cells against K562 targets, adult BM showed a clear lytic activity which could be further activated with IFN. In contrast, fetal BM was totally NK‐inactive also after IFN activation. Among healthy adult donors, autologous BM was lysed as efficiently as allogeneic BM, and when different NK cell donors were used, the same classification of these as NK high or low reactive cells was seen regardless of the source of BM targets. IFN could augment lysis in autologous as well as in allogeneic effector BM target combinations. IFN could also protect adult BM cells from NK lysis, but no protection was seen with fetal BM cells. The highest NK activity against BM targets was seen among nylon‐nonadherent, E rosette‐negative PBL and, therefore, the effector cell seemed to be of the same nature as that active against continuous cell lines.These results show that in the human NK system, NK cells can lyse normal BM cells and thymocytes. The higher sensitivity expressed by fetal BM cells and thymocytes as compared to adult cells may suggest an increased frequency of a particular primitive NK‐sensitive cell type in these tissues, a finding which is in line with results seen in the mouse NK system.