Goat anti-PA83 IgG titer. Serially diluted goat anti-PA83 IgG reacted with 10 nM rPA83 in a microplate ELISA. Titer calculated as the reciprocal of the dilution producing 50% maximum absorbance. Day 0 is 1st immunization with PA83-NT-MDP, asterisks indicate timings of 2nd (day 14), 3rd (day 28) and 4th (day 56) booster immunizations. Purified anti-PA83 IgG was obtained from plasmapheresed goats on day 94 (time point designated by a square).