Neonatal bacillus Calmette-Guérin vaccination induces adult-like IFN-γ production by CD4+ T lymphocytes

The immaturity of the neonatal immune system in mice is associated with defective IFN-γ production and Th2-biased immune responses. In this study, infants vaccinated at birth with BCG produced similar concentrations of IFN-γ in response to PPD and showed similar frequencies of IFN-γ-producing lymphocytes as compared to immune adults. Infants and adults produced only low concentrations of IL-4 and IL-5. CD4+ T lymphocytes were the main source of IFN-γ. Similar proportions of Th1 and Th0 PPD-specific T cell clones were observed in infants and adults. This study demonstrates that the human neonatal immune response to BCG is not biased towards Th2 and is characterized by the predominant production of IFN-γ by CD4+ T lymphocytes.