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New Research - March 2009The eosinophil rides againThe March 5, 2009, issue of the New England Journal of Medicine contains two original research articles and an editorial commentary dealing with the role of eosinophils in asthma. The two original articles involve the use of mepolizumab (anti-IL5) in the management of severe prednisone-dependent or prednisone unresponsive asthma. The editorial tries to put into perspective the findings of these two articles. Any reader of the AAAAI News is familiar with the tale of mepolizumab therapy for asthma. This issue has been discussed previously in the "News." A brief summary of this discussion is that it has been perplexing that mepolizumab has been found ineffective for asthma therapy to date, and yet has been effective for the treatment of eosinophilic syndrome. This paradox has puzzled investigators, and has put into question the role of the eosinophil as an effector cell in this disease. The two research articles in this issue of the New England Journal were designed to shed light on this paradox by studying the effect of mepolizumab in a different population of asthmatics, those with severe disease, resistant to, or not completely responsive to corticosteroid therapy. In these two articles, it was clearly shown that mepolizumab reduced exacerbations and improved the quality of life of this population of asthmatics. It also lowered eosinophil levels in sputum, bronchial biopsies, and blood. However, in one study (Haldar, et al.), it failed to affect daily symptoms, FEV1 after bronchodilator use, or airway hyperresponsiveness. In the other study (Nair, et al.), it did improve asthma control and FEV1. Thus, it can be concluded, on the basis of these two studies taken as a whole that the eosinophil does contribute to the genesis of asthma at least in severely affected patients who are relatively resistant to corticosteroids. Because in one study (Haldar, et al.), it did not improve daily symptoms and FEV1, whereas further prednisone administration did so, the authors hypothesized that other factors which are steroid responsive also play a role. They postulated that the other factor may be related to mast cell infiltration of smooth muscle in the airway. The editorial by Wenzel makes an attempt to put these articles into perspective. The theme of the editorial is that although these studies clearly show a role for eosinophils in this select group of severe asthmatics, the results may not apply to asthmatics as a whole, and therefore other mechanisms that are non-eosinophil dependent may be playing a very important role in the pathogenesis of this disease. Reference
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