Pertussis-specific cell-mediated immunity in infants after vaccination with a tricomponent acellular pertussis vaccine.

The aim of this study was to investigate pertussis-specific cell-mediated immunity in infants vaccinated with a tricomponent acellular vaccine. Infants were investigated during a primary vaccination schedule from the third month of life to the sixth month as well as before and after a booster at 15 to 24 months. This is the first report of specific cell-mediated immune responses to pertussis-related antigens in infants below the age of 12 months. Our data show that the vaccine induces T-cell responses specific for the vaccine components, detoxified pertussis toxin, filamentous hemagglutinin, and pertactin, that increase progressively over the course of the vaccination schedule. In contrast to declining antibody titers, cell-mediated immune responses are stable over the postprimary to prebooster period. Vaccination results in a progressive increase in the number of T cells that express activation marker CD45RO preferentially on CD4-positive T cells after stimulation with pertussis antigens. Measurements of cytokine secretion profiles demonstrated a preferential induction of interleukin 2- and gamma interferon-producing T-helper 1 cells and only low production of interleukin 10. The observed persistence of the specific cell-mediated immunity may have a bearing on the protective mechanisms induced by pertussis vaccination. Cell-mediated immunity requires further study, particularly to improve our understanding of the persistence of protection afforded by vaccination up to the administration of booster doses.