Tuesday, 25 November 2014

Aspergillus Protease Allergens have a Role in Asthma

Asthma is a debilitating disease characterised by airway inflammation, hyperresponsiveness and bronchoconstriction leading to symptoms such as wheeze, cough and breathlessness, and in severe cases even death.

Adults with severe asthma have significantly greater test reactivity to fungi (incl. Aspergillus fumigatus) compared with other well established allergens eg house dust mite and 50% of those with the most severe asthma attacks (i.e. those admitted to intensive care units) are sensitive to at least one fungal allergen .

Given these observations, the authors of this recent paper set out to discover if Aspergillus allergens have a role in the exacerbation of asthma and thus make symptoms far worse for the patient. They focused on a subset of Aspergillus allergens that not only provide a potential for allergic reaction in the patient, but also have an additionally destructive activity known as protease. Proteases can directly attack the surface of our lungs and airways, potentially destroying the delicate proteins that are so important to form the structure of the airways and the mechanisms that control infection and immunity. It is thought that these proteases could initiate the characteristic hyper-reactivity of the airways of a severe asthmatic.

The authors were able to remove two protease allergens from a strain of A. fumigatus that is known to induce asthma-like symptoms in mice. When tested in mice the effect was to reduce airway inflammation and airway remodelling, thus reducing two of the most prominent symptoms of asthma - hopefully this would be repeated if the same experiment was to be carried out in humans!

It is hoped that this result will highlight the importance of fungi in causing and exacerbating severe asthma and that more research can now be carried out on drugs which might block the activities of fungal allergens in these patients.

It is worth mentioning that there are two further allergic diseases that could benefit from this research. Allergic Bronchopulmonary Aspergillosis (ABPA) as well as Severe Asthma with Fungal Sensitivity (SAFS) prominently feature the growth of fungi (in particular Aspergillus) in the airways of the affected people. Perhaps protease allergens are one way that Aspergillus can gain a foothold in the lungs of these people and gradually grow?

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