Enhanced Pro-Inflammatory Response of Macrophages to Interleukin-33 in an Allergic Environment

Allergic asthma is common in childhood and is associated with a T-helper type 2 (Th2)-biased immunological response. Exacerbations of asthma are characterised by increased inflammation of the airways, which appears to be driven by interleukin (IL)-33 that can activate pulmonary macrophages. The Th2 cytokine environment of allergic asthma may contribute to exaggerated airway inflammation.

To test this, we assessed whether production of pro-inflammatory cytokines by IL-33-stimulated macrophages was enhanced in cells pre-treated with the key Th2 cytokines IL-4 and IL-13. We also investigated whether this was associated with altered expression of regulatory microRNAs (miRNAs).

RAW264.7 cells cultured with IL-4 and IL-13 for 48 h were stimulated with IL-33 for 4 h. Pro-inflammatory mediators were assessed using quantitative real-time PCR (RT-PCR). Expression of miRNAs was assessed using microarrays and RT-PCR. In further experiments, we examined whether resolvin E1 (RvE1), which promotes the resolution of experimental asthmatic inflammation in vivo, could suppress the enhanced response by treating cells with RvE1 concurrently with IL-33 stimulation.

In cells pre-treated with IL-4 and IL-13, expression of mRNA for Ccl3, Ccl5, Ccl17, Ccl24, and Il1b in response to IL-33 stimulation was significantly increased. This was paralleled by up-regulated expression of miR-155-5p, a miRNA that is predicted to regulate several aspects of allergic inflammation. RvE1 suppressed the enhanced production of Ccl3, Ccl5, Ccl24, and Il1b.

We conclude that IL-33-activated macrophages may contribute to the exaggerated airway inflammation in exacerbations of allergic asthma, and that RvE1 has potential as a therapeutic agent that targets macrophages.