Genetic ablation of PI3Kgamma results in defective IL-17RA signalling in T lymphocytes and increased IL-17 levels

The signalling molecule PI3Kgamma has been reported to play a key role in the immune system and the inflammatory response. In particular, it facilitates the migration of haemato-poietic cells to the site of inflammation. In this study, we reveal a novel role for PI3Kgamma in the regulation of the pro-inflammatory cytokine IL-17. Loss of PI3Kgamma or expression of a catalytically inactive mutant of PI3Kgamma in mice led to increased IL-17 production both in vitro and in vivo in response to various stimuli. The kinetic profile was unaltered from WT cells, with no effect on proliferation or other cytokines. Elevated levels of IL-17 were not due to an aberrant expansion of IL-17-producing cells. Furthermore, we also identified an increase in IL-17RA expression on PI3Kgamma(-/-) CD4(+) T cells, yet these cells exhibited impaired PI3K-dependent signalling in response to IL-17A, and subsequent NF-kappaB phosphorylation. In vivo, instillation of recombinant IL-17 into the airways of mice lacking PI3Kgamma signalling also resulted in reduced phosphorylation of Akt. Cell influx in response to IL-17 was also reduced in PI3Kgamma(-/-) lungs. These data demonstrate PI3Kgamma-dependent signalling downstream of IL-17RA, which plays a pivotal role in regulating IL-17 production in T cells.