By Emenyeonu Ogadimma, University of Sharjah

Inflammation associated with asthma and other allergic airway diseases can be significantly worsened by exposure to both house dust mite allergens and crystalline silica, according to a new study published in the journal Allergy.

The findings, based on laboratory experiments involving mice and human airway cells, reveal that combined exposure to these substances led to severe airway inflammation, resulting in narrowed airways, thickened airway walls, and excessive mucus production.

“The combination of house dust mite allergens and silica caused substantially more severe lung inflammation than exposure to the allergen alone,” said Rabih Halwani, Professor of Immunology at the University of Sharjah and a co-author.

“The affected lungs showed narrowing of the airways, accumulation of inflammatory cells, thickening of the airway walls, and increased mucus production.”

The study explored whether inhaled crystalline silica, a mineral particle commonly found in airborne dust in certain high-dust environments, could exacerbate allergic airway inflammation and diminish the effectiveness of corticosteroid treatment.

In their laboratory experiment, the researchers exposed mice to crystalline silica, house dust mite allergens, or a combination of both, and then assessed airway inflammation, mucus production, lung function, immune responses, and the molecular pathways involved in steroid activity.

“The animals also developed impaired lung function and a mixed immune response involving both eosinophilic and neutrophilic inflammation,” said Prof. Halwani. “Importantly, dexamethasone, a powerful corticosteroid, failed to adequately control these changes.”

Silica exposure may undermine asthma treatment

The authors, researchers at the University of Sharjah, emphasize that their findings remain preliminary. While the results were promising in mice, they caution that the work is still at the preclinical stage and must undergo rigorous clinical testing before any potential application in humans can be considered.

Nonetheless, they describe the study as a significant and novel contribution. “To our knowledge, this is the first study to demonstrate that the combination of crystalline silica and house dust mite allergens drives steroid hyporesponsiveness,” they write.

The researchers found that the animals’ condition worsened when they were exposed to these substances, triggering complex inflammatory responses. These responses activated DNA-sensing pathways, including STING signaling, while simultaneously disrupting glucocorticoid receptor function, a key mechanism through which steroids exert their anti-inflammatory effects.

Asthma is a chronic respiratory disease in which the airways become inflamed, narrowed, and overly sensitive. Inhaled corticosteroids remain among the most widely used treatments because they suppress airway inflammation and help control symptoms.

The chronic inflammatory disease remains a major health challenge. There were an estimated 363 million people suffering from asthma in 2023, causing approximately 442,000 deaths, according to the World Health Organization.

However, a subset of patients with severe asthma responds poorly to therapy, leaving them at greater risk of persistent symptoms, worsening lung function, and potentially life-threatening attacks. There is growing evidence that environmental exposures may play an important role in this reduced responsiveness to treatment.

According to the study, silica exposure profoundly altered the balance between two forms of the glucocorticoid receptor, the cellular protein through which steroids produce their anti-inflammatory effects. “The active form, known as GRα, was nearly absent, whereas GRβ, which can interfere with steroid activity, was increased. As a result, the lung tissue was less able to respond normally to corticosteroid treatment,” Prof. Halwani explained.

The researchers further linked this impaired steroid response to activation of the STING pathway, a cellular defense mechanism involved in detecting damage and infection. “STING normally forms part of the body’s defense system by detecting signs of cellular damage or infection and triggering an immune response,” noted Prof. Halwani. “However, excessive STING activation may contribute to persistent and harmful inflammation. In the silica-exposed lungs, STING and its associated signaling proteins were strongly activated, and this activity was not effectively suppressed by dexamethasone.”

Asthma and steroid resistance

Overall, the study provides evidence that exposure to silica-containing dust may exacerbate allergic airway disease and make inflammation more difficult to control with conventional corticosteroid treatment. The researchers identify excessive STING activation as a possible mechanism linking environmental dust exposure to persistent lung inflammation and impaired steroid responsiveness.

The findings are important because they may offer an explanation for why some asthma patients develop severe inflammation and resistance to treatment at the same time, according to Prof. Halwani. He added that the study raises the possibility that targeting the STING pathway could provide a novel therapeutic strategy for patients whose asthma responds poorly to corticosteroids.

Meanwhile, the study cautions against drawing premature clinical conclusions. Although the results point to STING as a promising therapeutic target, the authors do not establish H151 as a treatment for asthma. The findings are based solely on an experimental model. Prof. Halwani emphasized that additional studies are needed before STING can be definitively confirmed as a driver of silica-related steroid hyporesponsiveness.

To strengthen the evidence, the authors stress that further investigation, including experiments involving genetic deletion of STING, is required. Prof. Halwani said that the researchers would continue their investigations to determine whether eliminating the pathway can prevent or reverse the receptor abnormalities and inflammatory changes observed following silica exposure.

If confirmed in human studies, the findings could be particularly relevant to regions where populations are routinely exposed to desert dust storms or workplaces in which silica-containing particles are common. As such, the implications of the study may extend beyond asthma to occupational and environmental health policies.

The paper also highlights the growing global burden of environmental and occupational silica exposure, arguing that a better understanding of the underlying biological mechanisms is essential for both public health planning and clinical practice.

“By connecting silica-induced epithelial damage and self-DNA release with persistent STING activation, glucocorticoid receptor imbalance, and reduced steroid responsiveness, the study provides a possible biological explanation for why allergic airway inflammation may become harder to control in high-dust environments,” Prof. Halwani concluded.