Mice immunized with various amount of rRBD (µg) Anti-rRBDIgGtitersa Neutralization Titerb
TcdB TcdA
  0 Pre-immune <100 <4 <4
2 doses <100 NP NP
3 doses <100 <4 NP
  3 Pre-immune <100 <4 <4
2 doses 400 NP NP
3 doses 800 16 16
  10 Pre-immune <100 <4 <4
2 doses 400 NP NP
3 doses 3200 64 16
TcdARBDc 3 × 10 µg 800 <4 256
aThe titers were obtained with sera pooled from 6 mice
bThe neutralization titer against toxins was defined as the highest sample dilution which could prevent 50% cell rounding induced by toxins
cThe immunogenicity studies of TcdA RBD will be published elsewhere
*NP means not performed
Table 1: C. difficile toxin B neutralization titers of antisera from groups of 6 mice immunized 3 times with varying amounts of rRBD.