The eosinophils that contribute to inflammation and exacerbation of the asthmatic response had been known to scientists for some time. But another type of eosinophil has been discovered that, to the great surprise of Researchers at the University of Liege’s GIGA research centre, has been shown to play a protective and beneficial role. Their astonishing discovery is published in The Journal of Clinical Investigation (1).

During allergic reactions such as asthma, our immune system does not work correctly and responds in an abnormal way to harmless allergens present in the environment (pollen, dust mites etc.). In an asthmatic individual, the eosinophil cells – granulocytes that are produced in the bone marrow and which circulate in the body via the blood – are recruited to the lungs where they participate to the pathological manifestations associated with an asthmatic reaction. In an article published in The Journal of Clinical Investigation, researchers at the University of Liege have, for the first time,  identified the existence of a sub–group of eosinophils called resident eosinophils which are present in the lungs of healthy individuals and which, unlike inflammatory eosinophils, play a regulatory and protective role while maintaining the balance of the immune system and preventing it from responding in an abnormal way such as observed during an asthma attack. The discovery of these specific eosinophils offers promising therapeutic and prophylactic opportunities for the treatment and prevention of asthma.

A team of scientists directed by Professor Fabrice Bureau and Dr , researchers at ULg’s GIGA research centre, discovered this sub-type of eosinophil in mice and subsequently in humans. In mice, the nucleus of these resident eosinophils appears as a ring shape (or doughnut shape), which make them easily distinguishable from the other inflammatory eosinophils. In humans, all eosinophils have the same morphology, which could explain why the sub-types have only just been discovered. The researchers have also demonstrated, in both mice and humans, that the resident eosinophils carry an identical marker on their surface, the protein CD62L, which means that they are easily distinguishable from inflammatory eosinophils.

(1) "Lung-resident eosinophils represent a distinct regulatory eosinophil subset. Claire Mesnil et al. The Journal of Clinical Investigation.