FIG. 4.

Inhibition of toxin binding to HEp-2 cells by CNF1 MAbs. (A) Wild-type CNF1 and CNF2 were incubated with either 5 μg of MAb BF8 (IgA) or the isotype-matched control MAb NOS-E1 and then assessed to determine their capacity to bind to HEp-2 cells in a receptor binding ELISA. (B) Wild-type CNF1 and ΔN545 were incubated with either 5 μg of MAb NG8 (IgG2a) or the isotype-matched control MAb GC2 and assessed to determine their capacity to bind HEp-2 cells in a receptor binding ELISA. The data are the cumulative averages of triplicate readings from eight independent experiments for CNF1 and from two independent experiments for all other toxins; the error bars indicate the standard deviation above and below the mean. Data were analyzed by paired, two-tailed t tests, and P values are indicated. The values for wells containing toxin but no anti-CNF1 polyclonal sera served as background controls and were subtracted from all sample values (average background control value, 0.689 ± 0.33).