Vero cell cytotoxicity assays

The Vero cell cytotoxicity assay ha been described in detail elsewhere ²⁸. Vero cells grown in DMEM containing 10% FBS were seeded (5×10⁴ per mL) in 96 well cell culture plates and incubated at 37°C overnight. The cells were then overlaid with ricin (10 ng/mL, 150 pM) in the absence or presence of 5-fold serial dilutions of VHHs, and incubated at 37°C for 2 h. The cells were then washed and fresh medium applied. Cell viability was assessed 45-48 h later using CellTiter-Glo (Promega, Madison, WI).