Interleukin-18 expression, CD8+ T cells, and eosinophils in lungs of nonsmokers with fatal asthma

BACKGROUND: The process of airway inflammation in the lungs of nonsmokers who die of asthma (fatal asthma) has not been reported in detail. OBJECTIVE: To examine nonsmokers who had died of asthma to exclude chronic obstructive pulmonary disease and investigate pulmonary inflammatory cells and the expression of interleukin-18 (IL-18) and its receptor in lung tissues compared with those in patients with well-controlled mild asthma and nonsmokers. METHODS: Lung tissues were obtained at autopsy examination from 12 nonsmokers with fatal asthma, excluding cases of chronic obstructive pulmonary disease, and from 5 nonsmokers with well-controlled mild asthma and 10 nonsmokers who had undergone surgical resection for lung cancer. Pulmonary inflammatory cells were examined and the expression of the proinflammatory cytokine IL-18 and its receptor in the lungs was evaluated. RESULTS: The numbers of eosinophils and lymphocytes, but not basophils or macrophages, were significantly increased in the lungs of patients with fatal asthma compared with the other 2 groups. The lung neutrophil count did not differ significantly between the fatal and mild asthma groups but was significantly higher in the fatal asthma group than in nonsmokers. CD8(+) T cells, but not CD4(+) T cells, were significantly increased in the lungs of the fatal asthma group compared with the other 2 groups. IL-18 protein and IL-18 receptor were strongly expressed in the lungs in the fatal asthma group. CONCLUSION: Caspase-1 inhibitors, anti-IL-18 antibodies, anti-IL-18 receptor antibodies, IL-18 binding protein, or inhibitors of genes downstream of the IL-18 signal transduction pathway may be of clinical benefit for the treatment of patients with severe asthma.