Figure 5.  Established NK cell lines show heightened responsiveness to IL2 but not to IL15
The established NK cell clones I2/22 and 1608b had been grown for >1year in 20nM human IL2
and for ~1 month before this experiment in 200pM human IL2.
Cells were then washed and cultured for 3 days in serial dilutions of human IL2 or mouse IL15.
Conclusions
1.  Although fresh ex vivo immature and mature NK cells will only grow in high concentrations of
IL2, many long-term NK cell lines such as I2/22 and 1608b will grow well in relatively low concen-
trations of IL2.
2.  However, this elevated responsiveness to IL2 is not accompanied by a similarly elevated
responsiveness to IL15.
3.  This suggests that the heightened responsiveness to IL2 is due to an increase in the number
of high affinity IL2 receptors on cultured NK cells, rather than to enhanced signalling through the
shared low affinity receptor for IL2 and IL15 comprised of the IL2/IL15Rb chain and gc chain.
4.  This conclusion is supported by the finding that long-term cultured NK cells show increased
levels of IL2Ra chains but not IL2Rb chains on the cell surface [see below].