Selective growth of natural cytotoxic but not natural killer effector cells in interleukin-3

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Abstract
Interleukin-3 (IL-3) can promote the proliferation of certain classes of lymphocytes distinct from those that are dependent on interleukin-2 (IL-2) for growth1–5. Culture conditions for its production are identical to those required for IL-2 and in both cases the producer cell appears to be Thy 1.2+, Lyt1+, Lyt2− (refs 1–5). However, unlike the IL-2 responder cells, the cells that proliferate in IL-3 are generally Lyt2− (ref. 1). Here we have measured the natural cytotoxic (NC) activity as well as natural killer (NK) cell activity of the IL-3-dependent cells. Both of these activities are part of a repertoire of spontaneous cytotoxic functions found in mice that might serve in early defence against infectious agents or immunosurveillance against tumours in vivo6–12. We report a new finding that IL-3 selectively maintains NC cells but not NK cells in culture. This is in contrast to the known requirement for IL-2 in NK cell growth13. This provides a means of isolating NC cells from NK cells in the mouse as an initial step in the study of the relative contribution of these two cell types in tumour immunity.