FIGURE 2.

V_HH toxin-neutralizing and binding activities. A, monomeric V_HHs were tested for toxin-neutralizing activity in a Vero cell cytotoxicity assay, as described under “Materials and Methods.” V_HHs (at indicated concentrations) were mixed with ricin (10 ng/ml) and applied to Vero cells in triplicate. Cell viability was assessed 48 h later. Shown is a representative experiment with error bars indicating S.D. B, to assess relative affinity of select V_HHs for ricin, the V_HHs (at indicated concentrations) were applied in duplicate to microtiter plates coated with ricin. The EC₅₀ values are defined as the V_HH concentration (nm) that achieved half-maximal binding. Shown is a representative experiment with error bars indicating S.D. The experiments described in A and B were replicated at least three times.