Figure 2.

miRNA-mediated control of MAIT-cell development. MAIT cells are selected on MR1-expressing DP thymic cells. They proceed through several stages of development (S1–S3) as indicated by their surface expression of CD24 and CD44. The transition between S1 and S2 is heavily dependent on the presence of miRNAs as shown in Drosha-deficient mouse models. S2 MAIT cells begin to proliferate and develop into S3 effector MAIT cells defined by their expression of the transcription factors T-bet and RORγt. S2 cells can also exit the thymus, where they continue to proliferate and develop into S3 MAIT cells and migrate to peripheral tissues. It is postulated that some extra-thymically matured MAIT cells recirculate back to the thymus where they contribute to the thymic microenvironment and remain resident for extended periods of time. miR-181 is currently the only miRNA shown to be involved in MAIT cell development as indicated. MHC-related protein 1 (MR1), Double positive (DP), Stage 1 (S1), Stage 2 (S2), and Stage 3 (S3).