FIG. 6.

(A) Effects of IL-12 or IFN-γ on intracellular growth of Francisella. J774 cells (10⁵ cells/well) were infected at a multiplicity of infection of 10:1 with F. tularensis subsp. novicida with or without 5 or 50 ng of recombinant IL-12 or IFN-γ per ml for 1 h and were then treated for an additional 1 h with medium containing gentamicin. The cells were then treated for 24 h with or without IL-12 or IFN-γ. The cells were washed with Hanks balanced salt solution containing 0.1% gelatin, and the cell mixtures were lysed in 0.2% sodium deoxycholate and plated on TSA supplemented with 0.1% cysteine. The colonies were enumerated after 24 to 36 h of incubation at 37°C. (B) TNF-α levels in bacterial cultures treated with IL-12 or IFN-γ. The level of TNF-α production in culture supernatants after 24 h of treatment was measured by enzyme-linked immunosorbent assay. The results are shown as the means ± standard deviations. The differences in TNF-α levels between cells cultured with bacteria and IFN-γ and cells cultured with bacteria alone were significant (P < 0.005).