Fig 8. Dose-Response Titration of PND Ab for protection of mice from LAC/USA300 Dermonecrosis.

Groups of BALB/c mice (n = 4 except neg. controls, n = 3) were passively immunized s.c. with two-fold dilutions of PND Ab starting with a dose of 300 μl (panel A) or 24 μl (Panel B). 48 hours later, mice were challenged i.d. with 32 x 10⁶ (panel A) or 28 x 10⁶ (panel B) CFUs LAC/USA300. Two days later, all mice were euthanized and photographed and lesion areas determined (C). Group-specific lesion area data were plotted against dose and four parameter non-linear regression was used to determine the EC₅₀ of 14 μl (9.66 μg) (R² = 0.55) which represents the dose of PND-Ig which prevented 50% of the maximal lesion area. Antibody and neutralization titers from the sera of mice passively immunized with PND-Ig were determined by ELISA (D) and in the TNA (E) from serum obtained from individual mice on the day of challenge. Each circle represents an individual mouse data point and horizontal lines represent geometric means. Regression lines derived from the serum antibody and TNA data vs. dose were then used to interpolate the PA₅₀ and PN₅₀ which are expressed as reciprocal titers. The regression equation for PA₅₀ determination was log ELISA EC₅₀ = 0.9504 x log Dose + 1.75, and for PN₅₀ determination was log TNA ED₅₀ = 0.858 x log Dose + 0.3589.