Antigen-specific responses to diphtheria-tetanus-acellular pertussis vaccine in human infants are initially Th2 polarized

Immune responses to exogenous antigens in infant experimental animals displ ay various degrees of Th2 polarization. Preliminary evidence from small hum an studies suggest a similar age-dependent response pattern to vaccines, bu t detailed investigations on vaccine immunity during infancy have not yet b een undertaken. We report below the results of a comprehensive prospective study on responses to the tetanus component of the diphtheria, tetanus, ace llular pertussis (DTaP) vaccine in a cohort of 55 healthy children, employi ng peripheral blood mononuclear cells (PBMC) collected at the 2-, 4-, and 6 -month vaccinations and at 12 months. Antigen-specific production of interl eukin-4 (IL-4), IL-5, IL-6, IL-9, IL-10, IL-13, and gamma interferon (IFN-g amma) was determined at each sample point, in parallel with polyclonal (phy tohemagglutinin PHA-induced) cytokine responses. Our results indicate early and persistent Th2 responses to the vaccine, in contrast to a more delayed and transient pattern of IFN-gamma production, This initial disparity betw een the Th1 and Th2 components of the vaccine response was mirrored by patt erns of polyclonally induced cytokine production, suggesting that the delay ed maturation of the Th1 component of the vaccine response during infancy i s secondary to developmental processes occurring within the overall Th cell system.