FIG. 1.

Monocytes, but not human dendritic cells, secrete cytokines in response to F. tularensis SchuS4 infection. Primary human monocytes and donor-matched hDC were infected with F. tularensis SchuS4 at a MOI of 50. Twenty-four hours after infection, culture supernatants were analyzed for cytokines. Monocytes infected with F. tularensis SchuS4 secreted significantly more TNF-α, IL-6, IL-1β, MIP1β, and MIP-1α compared to monocytes from uninfected controls (P < 0.01 [*]). In contrast, DC failed to secrete cytokines in response to SchuS4 infection, and these values were significantly different from those of uninfected controls. hDC readily secreted significantly greater concentrations of TNF-α, IL-6, IL-1β, MIP-1β, and MIP-1α in response to LPS compared to DC from uninfected controls (P < 0.01 [**]). Thus, the absence of cytokine in SchuS4-infected hDC cultures was not due to a general defect in hDC recognition of microbial antigens. Values that are below the level of detection (BLD) are indicated. Data are representative of six experiments of similar design, using different donor cells of similar design. Values are means plus standard errors of the means (SEM) (error bars).