The number of IFN-c SFCs was significantly higher with splenocytes from VR2516 immunized mice as compared to VR1020 immunized mice when stimulated in vitro with PyCSP IVTT purified using NI-NTA resin (p = 0.013), MagneHis Ni-particles (p = 0.015) or PyCSP synthetic peptides (p = 0.003) ( Figure 3A ). There was no significant difference when splenocytes were stimulated with either unpurified IVTT or unpurified IVTT associated to Polybeads or Protein G beads ( Figure 3A ). Unexpectedly, the use of wells precoated with anti-HIS mAb to capture the tagged proteins was poorly effective with no difference noted between the VR2516 and VR1020 groups. Markedly higher background reactivity was noted with the unpurified or bound IVTT preparations as compared to the purified preparations, presumably due to the presence of high levels of LPS and proteins in the E. coli extract ( Figure 3A) .