Background: It is unclear why the neutrophil differential count in induced sputum (IS) from normal children is highly variable. Since levels of neutrophil chemoattractant cytokines and oxidative stress are determinants of airway neutrophilia in animal models, we sought to determine the association between IS neutrophils from healthy children and (i) interleukin-8 (IL-8) and (ii) the oxidative stress marker 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG).
Methods: IS was done using hypertonic saline. The proportion (differential %) and the absolute number of IS neutrophils were determined by light microscopy. IS IL-8 and 8-oxodG were determined using ELISA. Spearman's rank correlation (Rs) was used to assess relationship between variables.
Results: Adequate IS samples for analysis were obtained from 64/114 healthy children. The median (interquartile range) neutrophil differential count (n=64) was 20.6% (5.67-56), and absolute neutrophil count (n=53) was 0.11x10(6) (0.01-0.77). Both the % neutrophils, and the absolute neutrophil count were associated with IL-8 (Rs=0.67, p<0.0001 and 0.60, p<0.0001, respectively), but there was no association between IS neutrophil variables and 8-oxodG (n=40). The repeatability (intraclass correlation coefficient-Ri) of the neutrophil differential count was 0.58 (n=15).
Conclusions: The variation in the proportion and number of neutrophils in the lower airway of healthy children is associated with IL-8, but not with oxidative stress. The IS neutrophil differential count in healthy children is relatively stable over several months.