Study objectives: We investigated the role of two leukotriene B4 (LTB4) receptors, BLT1 and peroxisome proliferator-activated receptor (PPAR)-α, in conferring the susceptibility to develop COPD in smokers. Proinflammatory LTB4 activities are mediated by BLT1, while the inactivation of LTB4 is promoted by PPARα.
Patients and methods: BLT1 and PPARα proteins were quantified by immunohistochemistry in specimens obtained during lung surgery from 19 smokers with or without COPD and from 7 nonsmoking subjects.
Results: We have shown that the percentages of PPARα-positive alveolar macrophages and PPARα-positive cells in the alveolar wall were increased in COPD patients compared with control subjects. Moreover, the patients with COPD exhibited a significant increase of BLT1-positive alveolar macrophages compared with nonsmokers and an increased number of BLT1-positive cells in the alveolar walls compared with non-COPD smokers. In contrast, BLT1 and PPARα immunoreactivity did not differ significantly between nonsmokers and non-COPD smokers. Most of BLT1-positive cells in the alveolar walls were neutrophils and CD8 cells. While the number of neutrophils infiltrating the lung parenchyma was similar among the three groups, the number of CD8 T cells was increased in COPD patients, but there was no evidence that BLT1 was up-regulated specifically on these cells in COPD patients.
Conclusion: The results demonstrated that BLT1 and PPARα are detectable in alveolar macrophages and CD8 T cells in human lung tissue, and suggest that the dual LTB4 receptor system is up-regulated in the peripheral lungs of smokers who are susceptible to the development of COPD. This system might represent a novel target for therapeutic intervention in COPD patients.