Rationale: Among infectious diseases, tuberculosis (TB) is a leading cause of death worldwide. Accumulated knowledge has revealed that macrophages are deeply involved in the progression and pathogenesis of TB. We hypothesized that the evaluation of a macrophage activation marker may be useful in the diagnosis and assessment of pulmonary TB.
Objectives: To examine the utility of the macrophage activation marker soluble CD163 (sCD163) as a diagnostic tool and measure of disease severity for pulmonary TB and tuberculous pleurisy.
Methods: We compared the concentration of sCD163 in serum samples of 180 patients with active pulmonary TB with concentrations in serum samples of 45 age- and sex-matched control subjects. We also measured sCD163 in pleural fluid samples of 100 patients with pleural disease, including 31 patients with tuberculous pleurisy.
Measurements and main results: We found increased serum concentrations of sCD163 in patients with active pulmonary TB compared with those of control subjects (1,643 ± 1,737 ng/ml vs. 533.9 ± 49.3 ng/ml; P < 0.0001). sCD163 levels were also higher in pleural fluid samples of patients with pulmonary TB than in those of patients with non-TB pleurisy (5,239 ± 2,436 ng/ml vs. 2,877 ± 1,191 ng/ml; P < 0.0001). The levels of sCD163 in pleural effusions were significantly higher than serum levels obtained simultaneously from the same patients, particularly for patients with tuberculous pleurisy. Patients with a serum level of sCD163 above 1,300 ng/ml, had a mortality rate that was five times higher than that of patients with a lower sCD163 level (44.6% vs. 6.6%; P < 0.0001 by log-rank test). Microscopic examination of lung and pleural tissue samples showed concordance of enhanced CD163 expression with the presence of caseating granulomas in tissue obtained from patients with TB.
Conclusions: The macrophage activation marker CD163 was increased in patients with active pulmonary TB compared with age- and sex-matched control subjects. Increased levels of sCD163 were associated with increased mortality in patients with pulmonary TB. sCD163 also showed promise as a diagnostic tool for tuberculous pleurisy. These results warrant further study of sCD163 as a potentially useful biomarker for the diagnosis and assessment of pulmonary TB. Clinical trial registered with www.umin.ac.jp/ctr/index-j.htm (UMIN000003400).
Keywords: CD163; tuberculosis; tuberculous pleurisy.