Micro-RNA Profiling in CD4⁺ T Cell Differentiation.

Micro-RNAs comprise a class of small noncoding RNAs which have been found to be important regulators of cellular differentiation in multiple species. Previous analysis of micro-RNA expression in the murine hematopoietic system has suggested a role in cell differentiation and the maintenance of cell identity. Naïve progenitor CD4⁺ T cells respond to a combination of appropriate antigen and other specific signals by undergoing proliferation and further differentiation into one of at least two subsets. T helper 1 (TH1) cells produce high levels of the cytokine IFN-γ and T helper 2 (TH2) cells produce high levels of IL-4, optimizing them for control of intracellular and extracellular pathogens, respectively. It is currently not known whether micro-RNA molecules influence CD4⁺ T cell differentiation. We have used oligonucleotide arrays to analyze micro-RNA expression profiles of freshly isolated murine CD4⁺ T cells compared to cells differentiating into TH1 and TH2 subsets. Expression profiles were found to differ significantly between naïve and stimulated CD4⁺ cells, with fewer differences between TH1 and TH2 subsets. Promising candidate micro-RNAs are being further evaluated by northern blot and genetic studies. Micro-RNA-155 is upregulated on stimulation of CD4⁺ T cells in multiple oligonucleotide array assays. Micro-RNA-155 is encoded by the BIC oncogene and has been implicated in lymphomagenesis as well as in other malignancies. We have verified the induction of micro-RNA-155 in stimulated helper T cells by northern blot and are studying the effects of this micro-RNA on CD4⁺ T cell differentiation. Our observations support a role for micro-RNAs in helper T cell differentiation during the immune response.