# Dexamethasone inhibits IL-9 production by human T cells

## TL;DR

Dexamethasone significantly reduces IL-9 production by human T cells, which may explain part of its effectiveness in treating allergic diseases.

## Contribution

The study demonstrates that dexamethasone strongly inhibits IL-9 mRNA and protein levels in activated T cells.

## Key findings

- Dexamethasone reduced IL-9 mRNA levels to 0.7% of control values.
- Protein secretion of IL-9 was reduced to 2.8% of control values.
- The IC50 value of dexamethasone on IL-9 mRNA expression was 4 nM.

## Abstract

Interleukin 9 (IL-9) is produced by activated CD4+ T cells. Its effects include stimulation of mucus production, enhanced mast cell proliferation, enhanced eosinophil function, and IgE production. These effects are consistent with a role in allergic diseases. Glucocorticoids have potent anti-inflammatory effects, including suppression of cytokine synthesis, and are widely used in the treatment of allergic conditions.

We examined the effect of the glucocorticoid dexamethasone (Dex) on IL-9 mRNA expression and protein secretion with real-time RT-PCR and ELISA. Peripheral blood mononuclear cells (PBMC) were prepared from human volunteers and activated with OKT3. CD4+ T cells were purified from PBMC and activated with OKT3 plus PMA.

IL-9 mRNA abundance and protein secretion were both markedly reduced following treatment of activated PBMC with Dex. mRNA levels were reduced to 0.7% of control values and protein secretion was reduced to 2.8% of controls. In CD4+ T cells, Dex reduced protein secretion to a similar extent. The IC50 value of Dex on mRNA expression was 4 nM.

These results indicate that IL-9 production is very markedly inhibited by Dex. The findings raise the possibility that the beneficial effects of glucocorticoids in the treatment of allergic diseases are in part mediated by inhibition of IL-9 production.