Heterogeneity in diphtheria-tetanus-acellular pertussis vaccine-specific cellular immunity during infancy: Relationship to variations in the kineticsof postnatal maturation of systemic Th1 function

Cellular immunity to vaccines is highly variable during infancy. This study addressed the hypothesis that these responses are governed by the pace of maturational changes in adaptive immune competence, in particular, cellular functions that underlie the postnatal transition from Th2 to Th1 "bias." T etanus-specific cytokine responses were tracked in peripheral blood mononuc lear cells collected from infants at months 2, 4, 6, 12, and 18. These were compared with polyclonal responses. Results show that the Th2 component of the vaccine response develops rapidly and remains stable, unlike interfero n (IFN)-gamma production, which also is initiated early but commonly declin es after the final priming dose at 6 months. However, between 12 and 18 mon ths, the IFN-gamma component of the vaccine-specific response has a spontan eous resurgence that coincides with a parallel increase in overall IFN-gamm a production capacity. The Th2 component of vaccine-specific responses was more prominent in children with atopic family history.