Late increase of interleukin-18 levels in blood during Mycoplasma pneumoniae pneumonia.

To the Editor, we read with great interest the article by Chung et al. which appeared recently in the journal. In that paper the authors reported that the decreased IL-18 response in severe pneumonia group vs. non-severe group was observed regardless of asthma status of the patients, whose findings were somewhat different from ours on non-asthmatic patients which showed higher serum levels of IL-18 in severe cases of pneumonia than in mild cases in terms of both in children and in adults. In this point, the timing of venous sampling must be an important factor in explaining the discrepant results. Our previous results suggest that the level of IL-18 in blood as a marker of disease severity should cautiously be interpreted considering a timing of sampling; a value of IL-18 in a blood sample which is obtained at the first visit to the hospital does not always represent the highest level of IL-18 because of the fact that the time which elapsed from the onset of illness to the blood sampling may vary among patients. Analyses on sequential samples, therefore, must be necessary to fully understand the perplexing nature of cytokine activation during Mycoplasma pneumoniae infection.