Effects of allergic stimulation and glucocorticoids on miR-155 in CD4+ T-cells.

Rationale: MicroRNAs (miRNAs) are emerging as important regulators of allergic inflammation and potential therapeutic targets. We sought to identify which miRNAs are expressed in CD4⁺ T-cells and determine whether allergic stimuli or glucocorticoids alter their expression.

Methods: After IRB approval, blood was collected from dust mite (DM) allergic rhinitis subjects (n=20), non-allergic controls (n=8), and asthmatics (n=16). Peripheral blood mononuclear cells were incubated with dust mite extract (DME), diluent control, or DME + dexamethasone (0.1 µM). CD4⁺ T-cells were collected by magnetic bead column, and RNA was isolated by guanidinium/phenol-chloroform extraction. MicroRNA expression was measured using Nanostring microarray and quantitative real time PCR (qPCR).

Results: We identified 196 miRNAs that were stably expressed in circulating CD4⁺ T-cells. Allergen stimulation of CD4⁺ T-cells with DME differentially induced miR-155 expression in cells of DM-allergic subjects as compared to non-allergic subjects. Induction of miR-155 expression was also observed with anti-CD3/anti-CD28 simulation and phorbol-12-Myristate-13-Acetate (PMA) treatment, and further augmented by calcium inophore and bromocyclic AMP in the latter treatment. The level of miR-155 expression was positively associated with expression of the T_H2 cytokines IL-5 and IL-13. Inhibition of miR-155 in Jurkat T-cells inhibited the production of these cytokines. Glucocorticoids attenuated the effects of dust mite allergen, raising the possibility that inhibition of this miRNA could be a mechanism through which glucocorticoids exhibit their anti-inflammatory effects. The CD4⁺ T-cells had a higher level of miR-155 expression in asthma compared to in allergic rhinitis and non-asthmatics. The inhibitory effects of glucocorticoids on CD4⁺ T-cell miR-155 expression were lost in severe asthmatics.

Conclusion: Mir-155 is differentially expressed in allergic T-cells exposed to DM extract compared to in non-allergic cells and it is inhibited by glucocorticoids. MiR-155 may play a role in mediating allergic inflammation in T-cells and could be an anti-inflammatory target of steroids. This pathway may be de-regulated in severe asthma.