T cell maturation in the thymuses and spleens of Mettl8 conditional KO mice. (A) Schematic diagram of “conditional ready” (floxed) Mettl8 allele. Two loxP sites (red triangle) flanking the Mettl8 exon (blue square) within the 5′ and -3′ homology regions (∼1.5 kb, respectively) are indicated. (B) Relative expression of Mettl8 in CD3⁺ T cells from the spleens of Mettl8^fl/fl (WT) and Mettl8^fl/flCd4^cre (KO) mice, detected by qPCR. (C−E) Representative plots (C) and cumulative data (D and E) show different states of T cell development in the thymus of WT and KO mice as tested by flow cytometry. (F) Representative flow cytometry plots and cumulative data show the frequency and absolute number of CD44^hi CD62L^lo effector memory cells and CD44^lo CD62L^hi naïve cells gated on TCRβ⁺ CD24⁻ CD69⁻ mature CD4⁺ T cells (top) and mature CD8⁺ T cells (upper middle) from the thymuses, CD44^hi CD62L^lo active cells, CD44^lo CD62L^hi naïve cells, and CD44^hi CD62L^hi central memory cells gated on CD4⁺ T cells (lower middle) and mature CD8⁺ T cells (bottom) from the spleens of Mettl8^fl/flCd4^cre mice and littermate controls. (G) Representative flow cytometry plots and cumulative data show the frequency and absolute number of Foxp3⁺ CD4⁺ T cells the spleens (top) and the thymuses (bottom) of Mettl8^fl/flCd4^cre mice and littermate controls. (H) Body weight of enteritis mice induced by transfer of CD4⁺ T cell to Rag1^−/− mice and suppression by Mettl8^−/− or WT T_reg cells. n = 4–7 mice per group. Data are representative of two independent experiments. P value was calculated by two-tailed Student’s t test. P value was calculated by two-tailed Student’s t test; *P < 0.05; **P < 0.01; ***P < 0.001.