Activation of murine dendritic cells by OprF. Purified splenic dendritic cells (DCs) were pulsed with LPS (10 μg/ml), native (n) or recombinant (His) OprF at different concentrations for 18 hrs before the assessment of costimulatory molecule expression (A) and cytokine production (B and C). FACS analysis was done by staining with FITC and PE-conjugated mAbs to costimulatory molecules. Number represent percent of positive cells. Cytokine levels were determined in the culture supernatants by cytokine-specific ELISA. * Indicates P < .05 (cytokine production by LPS- or porin-pulsed versus unpulsed (-) DCs). ** Indicate P < .05 (cytokine production by n-OprF-pulsed tlr4-/- DCs versus n-OprF-pulsed WT DCs only and His-OprF-pulsed DCs versus n-OprF-pulsed DCs).