IL-12 SYNERGIZES WITH IL-2 TO INDUCE LYMPHOKINE-ACTIVATED CYTOTOXICITY AND PERFORIN AND GRANZYME GENE-EXPRESSION IN FRESH HUMAN NK CELLS

NK-mediated cytotoxicity is regulated by a variety of cytokines and is thought to involve perforin and granzymes, The effects of IL-2 and IL -12 on the expression and activation of cytolysis were examined in fre shly isolated human NK cells. A dose-dependent increase in cytolysis o f the NK-sensitive target cell, K562, and the NK-insensitive but lymph okine-activated killer (LAK) cell-sensitive target, UCLA-SO-M14, was o bserved after short term culture of purified human NK cells in either IL-2 or IL-12. Moreover, the two cytokines often synergized to produce augmented lytic activity. A suboptimal dose of IL-2 (60 IU/ml) combin ed with IL-12 (2 U/ml) could induce lytic activity equal to twice the additive effect of each cytokine alone. Northern analyses revealed tim e-dependent increases in mRNAs encoding for perforin and granzymes A a nd B following treatment with IL-2 alone or IL-2 plus IL-12. IL-2 and IL-12 also synergized for the induction of granzyme mRNAs, in that tre atment with both cytokines increased mRNA levels approximately 50% abo ve the sum of each cytokine alone, as quantitated by phosphorimage ana lysis, and normalized to GAPDH gene expression. However, the synergy b etween IL-2 and IL-12 for the induction of mRNA was less dramatic than for lytic activity. Results of experiments in which cytokine-treated cells were pulsed with actinomycin D indicated that the increased gran zyme and perforin gene mRNA levels in response to IL-2, IL-12, or the combination were not due to increased transcript stability. The data s uggest that low doses of IL-2 and IL-12 synergize to augment NK- and i nduce LAK-mediated cytotoxicity and that this increase is associated w ith enhanced transcription of perforin and granzyme genes in a synergi stic fashion. (C) 1995 Academic Press, Inc.