FIGURE 3 | Role of miR-181 and miR-155 in lymphocyte development.

a | Higher levels of miR-181 in double positive lymphocytes (DP cells) compared with mature T cells is accompanied by the higher sensitivity of the T-cell receptor to stimulation by MHC–peptide complexes. As miR-181 levels decrease during maturation, the activation threshold of T-cell receptors increases as a result of increased levels of several phosphatases modulated by miR-181 (see graph). b | Mir-155-null mice are characterized by complex defects in homeostasis of the immune system and globally impaired immune responses. Among the defects that were characterized in detail, the loss of miR-155-mediated inhibition of the transcription factor c-MAF led to increased production of interleukin-4 (IL-4) and T helper-2 (Th2) cells. The germinal centre reaction was disrupted, resulting in impaired T cell-dependent antibody responses (see main text).

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