TCR-dependent and -independent activation underlie liver-specific regulation of NKT cells

The fate of invariant NKT (iNKT) cells following activation remains controversial and unclear. We systemically examined how iNKT cells are regulated following TCR-dependent and -independent activation with α-galactosylceramide (αGC) or IL-18 plus IL-12, respectively. Our studies reveal activation by αGC or IL-18 plus IL-12 induced transient depletion of iNKT cells exclusively in the liver that was independent of caspase 3-mediated apoptosis. The loss of iNKT cells was followed by repopulation and expansion of phenotypically distinct cells via different mechanisms. Liver iNKT cell expansion following αGC, but not IL-18 plus IL-12, treatment required an intact spleen and IFN-γ. Additionally, IL-18 plus IL-12 induced a more prolonged expansion of liver iNKT cells compared with αGC. iNKT cells that repopulate the liver following αGC had higher levels of suppressive receptors PD-1 and Lag3, whereas those that repopulate the liver following IL-18 plus IL-12 had increased levels of TCR and ICOS. In contrast to acute treatment that caused a transient loss of iNKT cells, chronic αGC or IL-18 plus IL-12 treatment caused long-term systemic loss requiring an intact thymus for repopulation of the liver. This report reveals a previously undefined role for the liver in the depletion of activated iNKT cells. Additionally, TCR-dependent and -independent activation differentially regulate iNKT cell distribution and phenotype. These results provide new insights for understanding how iNKT cells are systemically regulated following activation.

Acute inflammation with IL-18/IL-12 or α-GalCer treatment induces liver iNKT cell apoptosis and repopulation from peripheral tissues, whereas chronic inflammation ablates systemic iNKT cells with thymic-dependent repopulation (134.24)

We previously showed that IL-18/IL-12 treatment of tumor bearing mice elicited significant anti-tumor activity concurrent with a decrease in the detectable number of invariant NKT (iNKT) cells. We now demonstrate that acute treatment with IL-18/IL-12 initially decreased the number of NK1.1(+) iNKT cells while α-GalCer decreased both NK1.1(+) and NK1.1(-) iNKT cells in the liver. Genomic qPCR analysis of iNKT cell's restricted Vα14Jα18 TCR confirmed the loss of cells at 24hrs in the liver rather than receptor down modulation. A small or no decrease in the genomic levels of Vα14Jα18 from other lymphoid tissues indicates the loss of iNKT cells from IL-18/IL-12 or α-GalCer treatment of mice was regulated by the liver microenvironment. Furthermore, an increase in AnnexinV was detected on liver iNKT cells following treatment with IL-18/IL-12 and an increase in cells that were tunnel positive was observed in the liver following α-GalCer treatment of mice. Although iNKT cells initially (24hrs) decrease in the liver following acute administration of α-GalCer or IL-18/IL-12, these cells subsequently (72hrs) reappear and expand in the liver. To study the expansion of iNKT cells in the liver, we administered BrdU to mice 24hrs after acute treatment with IL-18/IL-12 or α-GalCer and found a high percentage of proliferating liver iNKT cells were recent emigrating NK1.1(-) iNKT cells.