Characterization of the antigens. Titration curves of the MAbs were established
by ELISA on wells coated with crude extract of P. halstedii race 1. A
concentration of the biotinylated MAb which gives about 50% binding (2 to 4
mg/ml for MAb 18E2 and 0.5 to 1 mg/ml for MAb 12C9) was used for competition
experiments in combination with an equal concentration or a 2-, 10-, or 100-fold
excess of the unbiotinylated MAb.