Lipopolysaccharide stimulates the proliferation of human CD56(+)CD3(-) NK cells: A regulatory role of monocytes and IL-10

NK cells recognize and kill tumor cells and normal cells, and these play an important role in immune defense in cancer, infectious disease, and autoim munity. NK killing is regulated by positive or negative signals derived fro m the interaction of surface receptors with ligands on the target cells. Ho wever, the mechanisms controlling the proliferation and maintenance of NK c ells in normal human individuals are less clearly defined. In this study, u sing an entirely autologous system, we demonstrate that human peripheral bl ood CD3(-)CD56(+), killer cell-inhibitory receptor (KIR)-expressing cells p roliferate and expand in response to LPS, These responses are enhanced in t he presence of anti-IL-10 receptor-blocking Abs or on the removal of CD14() cells from the cultures. This enhancement is also reflected in substantia l increases in cytolytic activity and IFN-gamma production. The negative ef fect of CD14(+) cells may also be IL-10 mediated, IL-10 being lost from the culture supernatants of CD14-depleted PBMC and rIL-10 reversing the effect of this depletion. On the other hand, mRNA for the p35 and p40 subunits of IL-12 is still induced in CD14-depleted cultures. The expansion of CD3(-)C D56(+) cells was also inhibited by CTLA4-Ig, indicating a role for CD80/86, B lymphocytes were not required for the expansion of CD3(-)CD56(+) cells, whereas removal of MHC class II+ cells from CD14-depleted cultures resulted in a complete abrogation of these responses. Expansion of CD3(-)CD56(+) ce lls was reconstituted in MHC class II-depleted cell cultures by adding back monocyte-derived dendritic cells. These results indicate that the response s of CD3(-)CD56(+) NK cells to LPS may be driven by a MHC class II+ B7(+) C D14(-) peripheral population, most likely blood dendritic cells.