Figure 3.

Cytokine secretion of F. tularensis-infected macrophages. Uninfected J774 cells or cells infected with F. tularensis at an MOI of 500 for 2 h were washed and subsequently incubated in the presence of E. coli-derived LPS (50 ng/ml) for an additional 2 h. The average TNF-α secretion in pg/ml and SEM of quadruple samples (n = 4) from one out of 2 representative experiments is shown. In the absence of LPS, the cytokine levels were below the limit of detection for the assay (< 15 pg/ml) (data not shown). Francisella-infected or non-infected PEC cells were incubated for 24 h after gentamicin treatment and the average IL-1β secretion in pg/ml and SEM of 6 samples (n = 6) from one out of 2 representative experiments is presented. A Student´s 2-sided t-test, including the Bonferroni correction for multiple pair-wise comparisons, was used to determine whether the cytokine release induced by each of the strains or the uninfected control were significantly different to the parental strain (*, P ≤ 0.05; ***, P ≤ 0.001).