Background: Recent studies have demonstrated the usefulness of induced sputum in detecting the expression of Th2-type cytokines in asthmatics and have shown that the profile of inflammatory cells in induced sputum differs with time.
Objective: To determine whether the duration of sputum induction also affects the expression of Th2-type cytokines in induced sputum.
Methods: Induced sputum was collected from eight atopic asthmatics at two separated intervals (5 min each) during a 15 min sputum induction, and each sample was examined separately for cytokine expression and inflammatory cells. Using immunocytochemistry, interleukin (IL)-4 and IL-5 immunoreactivity, T lymphocytes (CD3), eosinophils (major basic protein), neutrophils (elastase), epithelial cells and macrophages (CD68) were compared in the induced sputum obtained from the 0 min to 5 min and the 10 min to 15 min samples.
Results: The number of immunoreactive-positive cells expressing IL-4 and IL-5 were significantly higher in the 10 to 15 min induced sputum sample than in the 0 min to 5 min induced sputum sample (P<0.05). The number of eosinophils was also significantly higher in the 10 min to 15 min sample than in the 0 min to 5 min sample (P<0.05). In contrast, the number of neutrophils was significantly higher in the 0 min to 5 min sample than in the 10 min to 15 min sample (P<0.01); T lymphocytes, macrophages and epithelial cells did not differ between the two samples.
Conclusion: This study demonstrates that the duration of sputum induction significantly affects the profile of inflammatory cells and Th2-type cytokine expression, and underscores the need for the standardization of induced sputum procedure.