THE INDUCTION OF NITRIC-OXIDE BY INTERLEUKIN-12 AND TUMOR-NECROSIS-FACTOR-ALPHA IN HUMAN NATURAL-KILLER-CELLS - RELATIONSHIP WITH THE REGULATION OF LYTIC ACTIVITY

We have investigated the interleukin-12 (IL-12) and tumor necrosis fac tor-alpha (TNF alpha)-induced regulation of human natural killer (NK) cell function and their relationship with nitric oxide (NO) generation . We demonstrate that both cytokines were efficient to trigger the tra nscription of the inducible nitric oxide synthase (iNOS) mRNA, as dete cted by reverse transcriptase-polymerase chain reaction (RT-PCR). West ern blot analysis and intracytoplasmic fluorescence showed that iNOS p rotein was also induced by both cytokines. However, our data indicate that NO does not play a significant role in the effector phase of the cytotoxic activity mediated by NK-stimulated cells, inasmuch as the ly tic activity was not affected in the presence of specific NO synthase inhibitors. When aminoguanidine (AMG), an inhibitor of iNOS, was added during the afferent phase of NK stimulation with IL-12 and TNF alpha, a subsequent increase in the lytic potential of the effector cells to wards the NK-sensitive target cells (K562) and lymphokine-activated ki ller (LAK) target cells (Daudi) was observed. Conversely, the addition of chemical NO donors during the afferent step resulted in a dose-dep endent inhibition of the NK and LAK cytotoxicity. Our data suggest tha t the enhancement of NK-cell cytotoxic activity resulting from iNOS in hibition may be correlated, at least in part, to an increase in interf eron-gamma production and granzyme B expression. (C) 1998 by The Ameri can Society of Hematology.