Deficiency Of Pi3-Kinase Catalytic Isoforms P110 Gamma And P110 Delta In Mice Enhances The Il17/G-Csf Axis And Induces Neutrophilia

Background: Phosphoinositide 3-kinase gamma (PI3K gamma) and PI3Kd are second messenger-generating enzymes with key roles in proliferation, differentiation, survival, and function of leukocytes. Deficiency of the catalytic subunits p110 gamma and p110 delta of PI3K. and PI3Kd in p110 gamma/delta(-/-)mice leads to defective B-and T-cell homeostasis. Here we examined the role of p110. and p110 delta in the homeostasis of neutrophils by analyzing p110 gamma(-/-), p110 delta(-/-) and p110 gamma/delta(-/-) mice.Methods: Neutrophils and T cells in leukocyte suspensions from the bone marrow (BM), blood, spleen and lung were analyzed by flow cytometry. Serum concentrations of IL-17, of the neutrophilic growth factor G-CSF, and of the neutrophil mobilizing CXC chemokines CXCL1/KC and CXCL2/MIP-2 were measured by Bio-Plex assay. Production of G-CSF and CXCL1/KC by IL-17-stimulated primary lung tissue cells were determined by ELISA, whereas IL-17-dependent signaling in lung tissue cells was analyzed by measuring Akt phosphorylation using immunoblot.Results: We found that in contrast to single knock-out mice, p110 gamma/delta(-/-)mice exhibited significantly elevated neutrophil counts in blood, spleen, and lung. Increased granulocytic differentiation stages in the bone marrow of p110 gamma/delta(-/-) mice were paralleled by increased serum concentrations of G-CSF, CXCL1/KC, and CXCL2/MIP-2. As IL-17 induces neutrophilia via the induction of G-CSF and CXC chemokines, we measured IL-17 and IL-17producing T cells. IL-17 serum concentrations and frequencies of IL-17+ splenic T cells were significantly increased in p110 gamma/delta(-/-) mice. Moreover, IFN-gamma+, IL-4+, and IL-5+ T cell subsets were drastically increased in p110 gamma/delta(-/-)mice, suggesting that IL-17(+) T cells were up-regulated in the context of a general percentage increase of other cytokine producing T cell subsets.Conclusions: We found that p110 gamma/delta deficiency in mice induces complex immunological changes, which might in concert contribute to neutrophilia. These findings emphasize a crucial but indirect role of both p110 gamma and p110 delta in the regulation of neutrophil homeostasis.