Earlier infantile immune maturation is related to higher DTP vaccine responses in children

There are large inter‐individual variations in vaccine‐specific antibody responses in children. We sought to investigate whether early‐life environmental factors and/or adaptive immune maturation were related to diphtheria–tetanus–pertussis (DTP) vaccine‐specific antibody levels at 18 months of age. In the prospective FARMFLORA birth‐cohort, including both farming and non‐farming families, children were immunized with DTP vaccine at 3, 5 and 12 months of age. DTP vaccine‐induced antibody levels were measured in plasma at 18 months of age. Infants’ blood samples obtained at birth, 3–5 days, 4, 18 and 36 months and at 8 years of age were analyzed for total CD4 + T‐ and B‐cell counts, proportions of naïve and memory T and B cells, and fractions of putative regulatory T cells by flow cytometry. Multivariate factor analysis was used to examine associations between immune variables and vaccine responses. The most apparent multivariate pattern was that higher anti‐DTP antibody titers at 18 months of age were associated with lower infantile total counts of T and B cells in the blood. Furthermore, lower infantile total T‐ and B‐cell blood counts were associated with higher proportions of circulating CD45RO + memory T cells and to lower proportions of α4β7 + naïve T cells later in childhood. The multivariate findings were corroborated in univariate correlation analyses. Sex, delivery mode and dairy farm exposure were unrelated to the magnitude of DTP‐specific antibody responses. Our results thus suggest that children with a more mature/activated infantile adaptive immunity respond with higher vaccine‐induced anti‐DTP antibody levels at 18 months of age.