Figure 4.

Competitive ELISA. Recombinant protective antigen (PA) was coated onto the wells of an ELISA plate. Wells then were incubated with anti-PA W2 Fab at the concentrations indicated. After incubation for 1 h at room temperature, anti-PA W2 Fab was removed from the wells, and mouse anti-PA monoclonal antibodies (MAbs) 14B7 and 2D3 [16, 23] were added to the wells. Bound MAbs were detected by the addition of peroxidase-conjugated anti–mouse antibody, followed by tetramethylbenzidine substrate. The binding to PA was calculated by dividing the optical density value in the absence of W2 by the optical density value in the presence of W2. ▪, 14B7; ▴, 2D3