Phenotypical and functional alterations during the expansion phase of invariant Vα14 natural killer T (Vα14i NKT) cells in mice primed with α-galactosylceramide

Invariant V alpha 14 natural killer T (V alpha 14i NKT) cells are a unique immunoregulatory T-cell population that is restricted by CD1d. The glycolipid alpha-galactosylceramide (alpha-GalCer) is presented by CD1d and causes robust V alpha 14i NKT-cell activation. Three days after injection of alpha-GalCer, V alpha 14i NKT cells vigorously increase in number and then gradually decrease to normal levels. In the present study, we found that the re-administration of alpha-GalCer into mice primed 3 days earlier causes a marked increase in serum interleukin-4 and interferon-gamma. Intracellular staining revealed that the only expanded V alpha 14i NKT cells are responsible for the enhanced cytokine production. The enhanced cytokine production was correlated with an increased number of V alpha 14i NKT cells after priming. Additionally, primed V alpha 14i NKT cells produced larger amounts of cytokine as compared with naive V alpha 14i NKT cells when cultured with alpha-GalCer-pulsed dendritic cells. Thus, we considered that a subset of expanded V alpha 14i NKT cells acquired a strong ability to produce cytokines. In contrast to mice primed 3 days earlier, cytokine production is markedly diminished in mice primed 7 days earlier. The expanded V alpha 14i NKT cells altered the surface phenotype (NK1.1(-) CD69(-)) and contained intracellular interferon-gamma. Additionally, we found that primed V alpha 14i NKT cells did not disappear or down-regulate surface TCR expression when re-injected with alpha-GalCer as compared with naive V alpha 14i NKT cells. These results demonstrate that the function and surface phenotype of V alpha 14i NKT cells is dramatically altered after alpha-GalCer priming.