Neutralizing Ab delays internalization of ricin.

<p>A. Neutralization of ricin cytotoxicity by mAbs is confirmed using MTS assays. H9 cells were premixed with Ab at 10 µg/ml, and then ricin was added to the indicated concentration. MTS dye reduction was measured 48 hr later. This is representative of >5 Ab neutralization assays, error bars indicate SEM. B. HeLa-DsRed cells were incubated with labeled ricin (green) for the indicated time in the presence or absence of RAC18 mAb and images obtained by confocal microscopy. The white bar indicates 10 µm. C. Quantitative analyses of internalization and colocalization of ricin. Data are collected from confocal images, including those shown in panel B. At least three distinct experiments were performed and the number of individual data points collected is indicated in the table in panel D. Colors of curves conform to colored lettering in the table. D. Affinity of Abs, and data obtained from internalization curves shown in panel C. Affinity was determined by Biacore analyses of mAbs captured via Fc and tested against soluble ricin. N is the number of cells imaged to obtain the data for analysis, and the p value (by F test) compares the internalization curve of each Ab to that of no Ab.