Background: Eosinophilic inflammation is known to play an important role in the pathogenesis of allergic diseases. Apoptosis, a form of programmed cell death, is characterized by morphologic cell changes and leads to recognition and ingestion by macrophages. Apoptosis could be an important mechanism controlling the resolution of tissue eosinophilia.
Objective: This study was designed to investigate the presence of apoptotic eosinophils in induced sputum of patients with seasonal allergic rhinitis (SAR), when examined during natural pollen exposure and of patients with perennial asthma of different degrees of severity.
Methods: We recruited 11 patients with SAR to grass pollens, 26 patients with asymptomatic asthma (AA), and 18 patients with symptomatic asthma (SA). The severity of asthma was assessed by clinical scoring. Sputum was induced following a standard method and differential cell count was estimated. Eosinophils showing cell shrinkage and nuclear coalescence were classified as apoptotic. The number of apoptotic eosinophils was expressed as the percentage of total cells in sputum and as the proportion of apoptotic eosinophils relative to normal bilobed eosinophils ("apoptotic ratio").
Results: We found the number of eosinophils in the SA group was significantly greater than that in the SAR and the AA groups (P < .001 and P < .0001 respectively). The number of apoptotic eosinophils in the AA group was significantly lower than that in the SAR group (P < .001) and in the SA group (P < .0001). The apoptotic ratio for eosinophils in the SAR group was significantly greater than in the AA group (P < .05) and in the SA group (P < .05). There was no difference in the apoptotic ratio between the AA and SA groups.
Conclusions: This study confirms that apoptotic eosinophils are detectable in induced sputum of allergic patients. Further, the results of our study suggest that apoptosis could be an important mechanism in the control of acute eosinophilic inflammation in patients with SAR exposed to the sensitizing antigens. It appears that the apoptotic mechanism could be less effective in controlling tissue eosinophilia in asthmatic patients with chronic eosinophilic inflammation.