Differential regulation of NK cell proliferation by type I and type II IFN.

IFN, produced during viral infections by accessory (type I IFN) or NK cells (type II IFN), play a primary role in the regulation of immune and anti-viral NK cell effector functions. Because IFN have anti-proliferative effects on several cell types, including hematopoietic cells, we asked whether they modulate proliferation of human NK cells, and whether IFN-alpha and IFN-gamma mediate distinct effects on NK cells at different developmental stages. Analysis of proliferation at the single-cell level in human NK cells indicated that both IFN types inhibit IL-4-induced accumulation of immature CD56(-) IL-13(+) NK cells in freshly separated peripheral blood lymphocytes and in cells derived from them after short-term cultures. However, IFN-gamma inhibited specifically the IL-4-dependent proliferation of these cells without affecting the IL-2-dependent one or that of the IL-13(-) cells, whereas IFN-alpha attenuated proliferation of NK cells at any developmental stage (both immature CD56(-)IL-13(+) and mature CD56(+)IL-13(-) IFN-gamma(+) NK cells) and contributed to their monokine-induced differentiation to IFN-gamma-producing cells. Adding to our previous report that IL-13 inhibits accumulation of mature IFN-gamma(+) NK cells, the present data unravel a mechanism by which peripheral immature IL-13(+) and mature IFN-gamma(+) NK cells can negatively regulate each other's accumulation.