Figure 3.

The juvenile T-cell response to influenza A virus. Recruitment of CD4⁺ and CD8⁺ T cells to the lungs is delayed and diminished relative to that of adults. Regulatory T cells are recruited in similar numbers. Production of inflammatory and suppressive cytokines IFN-γ and IL-10 is reduced. In neonates, there is a mixed T-helper cell type 1 (Th1) and Th2 response that contributes to increased levels of IL-4. As juveniles age, there is a shift to a Th1 response. In addition, neonates have less TCR variability, which increases as they age, as well as an increased propensity to induce stable Foxp3 expression, which decreases as they age. γδ T cells are a source of IL-17 in neonates and promote tissue recovery by inducing amphiregulin. DN NKT cells rapidly expand and exhibit the ability to suppress CD4⁺ T cells. DN NKT = double-negative natural-killer T cell.