Fractional analysis of Th2-type cytokines in sequential samples of induced sputum

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.

To determine whether the duration of sputum induction also affects the expression of Th2-type cytokines in induced sputum.

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.

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.

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.