In vitro production of different interferon types by cloned human NK cells

Human peripheral blood null cells were conjugated in vitro with K-562 cells and expanded into continuous cell lines using IL-2 containing medium (CM) and periodical restimulation with phytohaemagglutinin (PHA). Most of these lines were made up of granular blasts expressing high natural killer (NK) activity. When analysed for different surface markers, the large majority of the blasts were E rosette+, T3+, Tac+, DR+, Leu7+ with a variable proportion of cells expressing T8 and M1 antigens (range: 20-80%). In contrast, T4 antigen was expressed by the majority of cells of the control cell lines originated in the absence of K-562 cells. Twenty-nine clones were obtained from one of the above lines using the limiting dilution technique and subsequently maintained in CM for 4 months or more. The majority of these clones maintained their cytotoxic potential and were able to produce different interferon (IFN) types (IFN-alpha, IFN-gamma or both) when growing in CM. In addition in a number of selected clones, simultaneous stimulation with PHA and K-562 cells was able to induce or support the production of both IFN types.