T Cell-Specific Inactivation of the PI3K p110α Catalytic Subunit: Effect in T Cell Differentiation and Antigen-Specific Responses.

Class IA PI3K p110δ and p110α subunits participate in TCR and costimulatory receptor signals involved in T cell-mediated immunity, but the role of p110α is not completely understood. Here, we analyzed a mouse model of the Cre-dependent functional inactivation of p110α (kinase dead) in T lymphocytes (p110αKD-T, KD). KD mice showed increased cellularity in thymus and spleen and altered T cell differentiation with increased number of CD4+CD8+ DP thymocytes, enhanced proportion of CD4+ SP lymphocytes linked to altered apoptosis, lower Treg cells, and increased AKT and ERK phosphorylation in activated thymocytes. In the spleen, the percentages of CD4+ Treg cells and CD8+ naive lymphocytes were reduced. In vitro, the differentiation of CD4+ cells from p110αKD-T mice showed lower induced Treg (iTreg) cell yield or IL-10 secretion. Moreover, Tfh cell yield, IL-21 secretion, and PI3-K-dependent elongation were hampered, as was Erk and Akt activation. Th1 or Th17 differentiation in vitro was not altered. The immunization of p110α-KD-T mice with KLH protein antigen induced an enhanced proportion of CXCR5+ CD4+ cells and germinal center B cells, increased ICOS expression in CD4+ cells, or IFN-γ secretion upon antigen re-activation in vitro. However, anti-KLH antibody responses in serum was similar in WT or p110α KD mice. These data show that T cell-specific p110α inactivation alters T cell differentiation and function.