Therefore, VA10 cell layers were infected at a multiplicity of infection (MOI) of 50:1 from the apical side with wild-type B. pertussis Tohama I strain (Bp-WT) that produces both CyaA and PT toxins, or by its Bp-CyaA-AC–, Bp-PT– or Bp-CyaA-AC–PT– toxoid-secreting isogenic mutants, respectively (Figure 4a). This evidence concerns the gene F2 and infection.