FIG. 4.

Stimulation of cytokine production in U937 cells treated with formalin-killed Y. pestis. (A) U937 cells were stimulated with FKB-27 (▴) and FKB-37 (•). The supernatants collected from FKB-27 (Δ) and FKB-37 (○) stock suspensions obtained by centrifugation were also used to stimulate the cells. The cytokine levels in the culture supernatant were determined by ELISA. The data are presented as the means ± standard errors for triplicate samples. A representative result from three independent experiments is shown. (B) The amount of free LPS released from each FKB was estimated by use of an Endospecy test kit. The activity level in each supernatant (Sup.), measured as the absorbance (A.) at 405 nm, was compared to that of the corresponding LPS. Data are presented as the means ± standard errors for duplicate samples. A representative result from two independent experiments is shown.