MicroRNA-mediated regulation of T helper cell differentiation and plasticity

T helper (TH) cells are a central component of the adaptive immune system. They coordinate cellular and humoral responses by producing cytokines and growth factors. Several TH cell subsets have been described, including TH1, TH2, TH9, TH17 and TH22 cells, regulatory T (TReg) cells and T follicular helper (TFH) cells.MicroRNAs are small evolutionarily conserved nucleotide sequences that regulate gene expression by interfering with mRNA translation and stability.MicroRNA-deficient CD4+ T cells show impaired survival and proliferation, but also have an increased sensitivity to signals that induce effector TH cell differentiation and cytokine production.An increasing number of individual microRNAs and co-expressed microRNA clusters have been shown to have marked effects on TH cell fate decisions and immune functions.MicroRNAs are crucial for the proper regulation of TReg cell development, homeostasis and plasticity, and for the maintenance of immune tolerance.Research on microRNA function can be used as a tool for the discovery of novel pathways that regulate TH cell biology and might identify novel targets for the treatment of conditions in which TH cell functions are impaired or exaggerated.