Mechanism of K562-induced human natural killer cell inactivation using highly enriched effector cells isolated via a new single-step sheep erythrocyte rosette assay

Abstract

In this study, we used preparations highly enriched in human natural killer (NK) cells to further characterize the mechanism of taget-cell-induced NK inactivation. Highly enriched populations of NK cells were obtained by a newly developed, single-step sheep red blood cell rosette assay. This method, which did not require any incubation steps to facilitate cell contact, permitted a rapid and efficient isolation if NK cells from adherent-cell-depleted peripheral blood lymphocytes. The non-rosetted cells had high NK activity, possessed large granular lymphocyte (LGL) morphology and expressed the NK-associated antigens Leu-11a, Leu-7, OKM1 and NKH-1. In contrast, the rosetted cells had significantly lower NK activity, possessed typical lymphocyte morphology and expressed the T-cell-associated marker OKT3.

Next, we examined the ability of these NK-enriched effector cells (EC_c) to become inactivated by K562. Functional studies revealed that EC_c lost $\text{≥95\%}$ of their lytic capacity following incubation with K562 at a ratio of 2/1 for 6 h. However, to achieve this level of inactivation, it was essential that the cell suspension be gently mixed every 90–120 min. Inactivation was not due to cell death and did not reflect changes in the percentages of cells bearing the Leu-11a, Leu-7, OKM1 and NKH-1 antigens, but was associated with an increase in cell surface concentration of OKM1. As judged by gross morphology, the percentages of LGL in EC_c before and after treatment with K562 were essentially the same. Finally, K562-treated EC_c also lost their ability to mediate antibody-dependent cellular cytotoxicity (ADCC), suggesting that both NK-cell-mediated cytotoxicity and ADCC may involve a common lytic pathway.