The second B. pertussis challenge was followed by similar increases (about 10-fold increase in IgG titers from the pre-reexposure levels to week 1 post re-exposure IgG titers) in serum anti-PT and anti-FHA IgG antibodies in all convalescent animals, regardless of their initial inoculation route (Fig. 4C), showing that even in the absence of detectable colonization, second exposure to B. pertussis boosted the antibody responses in animals primed by a first infection. The gene discussed is F2; the disease is infection.