NATURAL KILLER (NK) ACTIVITY OF NORMAL HUMAN PERIPHERAL BLOOD LYMPHOCYTES AGAINST ERYTHROLEUKEMIC CELL LINE K 562

Human peripheral blood lymphocytes of healthy donors showed significant levels of natural killer (NK) activity against erythroleukemic cell line K 562 in 3-hour 51Cr release assays. The levels of NK activity showed much individual variation, which was considered to be an individual trait that varied little under physiological conditions. The NK activity of mononuclear leukocytes from cord blood was very low, but increased early in infancy to the adult level.　　

The effect of contamination of the lymphocyte preparation with granulocytes or red blood cells was examined. When red blood cells were added in a ratio of 10 : 1 or more, NK activity was significantly suppressed. On the other hand, contaminating granulocytes had no effect on NK activity. Pre-treatment of lymphocytes with Tris-buffered ammonium chloride drastically obliterated the NK activity of these cells; so this treatment should be avoided.　　

When monocytes were removed from mononuclear cell preparations, the NK activity increased in many cases, but the magnitude of augmentation varied from donor to donor and from day to day. The possibility of monocyte-NK cell interaction was discussed.　　

In order to minimize the day-to-day fluctuation of NK assay conditions, peripheral blood mononuclear leukocytes were cryopreserved. These cryopreserved cells retained more than 80% of their NK activity.