IL-12/IL-18-dependent IFN-gamma release by murine dendritic cells

Dendritic cells (dc) develop in GM-CSF-stimulated cultures from murine bone marrow progenitors in serum-free (or low serum) medium. CD11c(+) myeloid D C from 7-day cultures stimulated with TNF-a, IFN-a, IFN-gamma, or LPS up-re gulated surface expression of CD40 and CD86 costimulator and MHC class II m olecules, did not up-regulate the low "spontaneous" release of IL-18, and d id not release IFN-gamma. Stimulation of in vitro-generated DC with exogeno us IL-12 and IL-18 (but not with IL-4 or LPS plus IL-18) induced IFN-gamma expression and release in 15-20% of the DC (detectable by FACS analyses or ELISA). Endogenous IL-12 p70 produced by DC in response to ligation of CD40 stimulated IFN-gamma release when exogenous IL-18 was supplied. In vivo-ge nerated, splenic CD8 alpha (+) and CD8 alpha (-) DC (from immunocompetent a nd immunodeficient H-2(d) and H-2(b) mice) cultured with IL-12 and IL-18 re leased IFN-gamma. The presence of LPS during the stimulation of DC with IL- 18 plus endogenous (CD40 ligation) or exogenous IL-12 did not affect their IFN-gamma release. In contrast, splenic DC pretreated in vitro or in vivo b y LPS strikingly down-regulated IFN-gamma release in response to stimulatio n by IL-18 and (endogenous or exogenous) IL-12. Hence, DC are a source of e arly IFN-gamma generated in response to a cascade of cytokine- and/or cell- derived signals that can be positively and negatively regulated.