GPR18 expression rescues the IEL defect in Gpr18^−/− mice. (A) CD45.2⁺ Gpr18^−/− BM transduced with empty vector (GFP-EV) or GFP-Gpr18 retrovirus was used to reconstitute CD45.1⁺ recipients. IELs were stained for the subsets as indicated. Numbers indicate percentage of cells in each gate. (B) Summary data of the type in A, shown as the ratio of donor-derived GFP⁺ to GFP⁻ cells of the indicated types (left) or as number of GFP⁺ CD8αα γδT IELs (right). (C) Flow cytometry of Thy1 expression in the CD8αα γδT IELs from BM chimeras, color coded as on the right. Graph shows summary data for the frequency of Thy1^hi cells in the same gated CD8αα γδT IEL populations (GFP⁺ and GFP⁻ Gpr18^−/− CD45.2⁺ and endogenous radio-resistant WT CD45.1⁺ cells). Each symbol in B and C represents an individual mouse, and the small horizontal lines indicate the mean. ***, P ≤ 0.001 (Student’s t test). Data are representative of three experiments.