Thus, it would seem that the PT neutralization effect at the CHO cell assay is mainly because of IgG anti-PT antibodies – either because of a specific function of the IgG anti-PT antibodies, or because of the major presence of IgG anti-PT in comparison with IgM and IgA anti-PT antibodies both after pertussis vaccination and after pertussis infection. This evidence concerns the gene F2 and pertussis.