BACTERIAL-DNA INDUCES MURINE INTERFERON-GAMMA PRODUCTION BY STIMULATION OF INTERLEUKIN-12 AND TUMOR-NECROSIS-FACTOR-ALPHA

Bacterial, but not mammalian DNA, can induce interferon-gamma (IFN-gam ma) in murine splenocytes. To elucidate the basis of this activity, we have assessed in vitro cytokine production by C3H/HeJ splenocytes sti mulated with either DNA from Escherichia coil or a synthetic oligonucl eotide containing an active palindromic sequence identified from DNA. Both DNAs induced IFN-gamma production, with the requirement for intac t DNA shown by sensitivity to DNase digestion. Fractionated cell popul ations were evaluated to determine direct or indirect cellular effects of the DNA. Although bacterial DNA failed to induce IFN-gamma in the nonadherent cell population, supernatants from adherent cells stimulat ed by DNA induced IFN-gamma production by these cells. Interleukin-l2 (IL-12) was detectable in supernatants from DNA-stimulated splenocytes before IFN-gamma, and neutralizing antibodies directed against IL-12 markedly inhibited the induction of IFN-gamma. Anti-tumor necrosis fac tor-alpha (TNF-alpha) antibodies also inhibited IFN-gamma production, and the combination of both anti-IL-12 and anti-TNF-a could totally in hibit production of IFN-gamma. Taken together, these results indicate that the stimulation of IFN-gamma production by bacterial DNA is media ted by IL-12 and TNF-alpha and point to macrophages/monocytes as targe ts of action of this macromolecule. (C) 1996 Academic Press, Inc.