Regulation of membrane phospholipid asymmetry by Notch-mediated flippase expression controls the number of intraepithelial TCRαβ(+)CD8αα(+) T cells

Intestinal intraepithelial lymphocytes (IELs) expressing CD8αα on αβ T cells (TCRαβ(+)CD8αα(+) IELs) have suppressive capabilities in enterocolitis, but the mechanism that maintains homeostasis and cell number is not fully understood. Here, we demonstrated that the number of TCRαβ(+)CD8αα(+) IELs was severely reduced in mice lacking recombination signal binding protein for immunoglobulin kappa J region (Rbpj) or Notch1 and Notch2 in T cells. Rbpj-deficient TCRαβ(+)CD8αα(+) IELs expressed low levels of Atp8a2, which encodes a protein with flippase activity that regulates phospholipid asymmetry of plasma membrane such as flipping phosphatidylserine in the inner leaflet of plasma membrane. Rbpj-deficient TCRαβ(+)CD8αα(+) IELs cannot maintain phosphatidylserine in the inner leaflet of the plasma membrane. Furthermore, depletion of intestinal macrophages restored TCRαβ(+)CD8αα(+) IELs in Rbpj-deficient mice, suggesting that exposure of phosphatidylserine on the plasma membrane in Rbpj-deficient TCRαβ(+)CD8αα(+) IELs acts as an “eat-me” signal. Together, these results revealed that Notch–Atp8a2 is a fundamental regulator for IELs and highlighted that membrane phospholipid asymmetry controlled by Notch-mediated flippase expression is a critical determinant in setting or balancing the number of TCRαβ(+)CD8αα(+) IELs.