In vitro protection against LeTx cytotoxicity. J774A.1 cells were treated with 50 ng (~2.9 nM) LeTx and varying concentrations of goat anti-sera. Cell viability determined by an MTT-based assay. A. Anti-PA83 IgG. Data shown are the average ± SEM of five assays each with four replicates. EC50 is 2.57 × 10-7 M. B. Anti-PA83 F(ab')2 fragment. Data shown are the average ± SEM of three assays each with four replicates. EC50 is 4.0 × 10-7 M, comparable to full length IgG. Curves and EC50 were generated using GraphPad Prism® V4.03.