YKL-40, a matrix protein of specific granules in neutrophils, is elevated in serum of patients with community-acquired pneumonia requiring hospitalization

The serum concentration of YKL-40, a matrix protein of specific granules in neutrophils, was determined by RIA in 90 patients hospitalized with pneumo nia of suspected bacterial origin. Of these, 64 were followed prospectively during antibiotic treatment with blood samples taken on day 0 ton admissio n and the start of treatment) and on days 1, 3, 5, 7, 10, and 21. Serum YKL -40 at admission was increased in patients with Streptococcus pneumoniae pn eumonia (median, 893 mu g/L; 95% confidence interval [CI], 704-1560), compa red with healthy subjects (median, 102 mu g/L; 95% CI, 64-247 mu g/L; P<.00 1) and in patients with pneumonia of unknown etiology (median, 448 mu g/L; 95% CI, 334-700; P <.05), Peak YKL-40 serum values were observed on day 1 a nd thereafter declined steeply to almost normal by day 3, During the first 10 days, there was a close relation between serum YKL-40 and markers of spe cific granules of neutrophils (serum lactoferrin and neutrophil gelatinase- associated lipocalin), which suggests that serum YKL-40 reflects exocytosis of specific granules of neutrophils in persons with acute bacterial pneumo nia.