Figure 7. RTB-B7 neutralizes ricin when toxin is pre-bound to receptor.

(A) To examine antibody recognition of receptor bound ricin, ELISA plates were coated with ricin or ASF overnight. ASF coated plates where then incubated with ricin while the remaining wells were incubated with 2% PBS-goat serum. RTB-B7 was serial diluted and added to the wells and developed as described in Materials and Methods. BSA wells were used to control for background. (B) To examine toxin neutralizing activity, THP-1 cells were treated with ricin for 30 min at 4°C, then washed and incubated with antibody or medium alone for 30 min at 4°C. Then, THP-1 cells where transferred to 37°C and 48 h later cell viability was measured as described in Materials and Methods. Viability was normalized to medium only treated cells and ricin-only treated cells determined the potency of the toxin in this assay. The ricin-only control cells were <20% viable. The data shown represent a single experiment in which each sample was done in triplicate or quadruplicate and repeated at least twice. Data are expressed as the mean ± SD.