FIG. 1.

Linearity of the in vitro neutrophil chemotaxis assay in response to live E. coli CP9 (wild type), CP921 (O-antigen deficient), and CP9.137 (capsule deficient). A total of 5 × 10⁵ purified human neutrophils was placed in the upper well of a chemotaxis chamber, with various titers of CP9, CP921, and CP9.137 placed in the lower chamber. Neutrophils that migrated into the lower chamber (following incubation at 37°C for 30 min) in response to the E. coli were quantitated by flow cytometry. Results demonstrate that this chemotaxis assay was linear from 3 × 10⁶ to 1 × 10⁸ CFU of E. coli (R² = 0.97, 0.95, and 0.96 for CP9, CP921, and CP9.137, respectively).