To advance our understanding of age-related differences in Bp-specific CD4+ T-cell responsiveness, we compared cytokine profiles, proliferative capacity and phenotype of Bp-specific CD4+ T-cell populations detectable in time after a clinically symptomatic Bp infection in children, adults and older adult participants in a unique cohort of ex-pertussis cases, sharing a history of primary whole cell pertussis vaccination during infancy. The gene discussed is CD4; the disease is pertussis.