[Significance of serum surfactant protein-D (SP-D) level in patients with pulmonary tuberculosis].

Elevated levels of serum surfactant protein-D (SP-D) have been previously reported in patients with idiopathic pulmonary fibrosis (IPF) and pulmonary alveolar proteinosis. To determine whether the same change is seen in other pulmonary diseases, especially pulmonary tuberculosis (TB), we measured the serum SP-D levels in active pulmonary TB (smear and/or culture: positive), acute interstitial pneumonia (AIP), IPF, acute exacerbation of IPF, hypersensitivity pneumonitis (HP), pneumoconiosis, bronchiectasis, and bacterial pneumonia by an enzyme-linked immunosorbent assay using monoclonal antibodies to human lung SP-D, and compared them with those of healthy elderly subjects over 50 years of age. The SP-D level in the healthy elderly subjects was 57.6 +/- 38.4 ng/ml (mean +/- SD, n = 287). The levels in patients with active pulmonary TB (140.6 +/- 18.2 ng/ml, n = 49), AIP (1,021 ng/ml, n = 1), IPF (307.0 +/- 180.7 ng/ml, n = 42), acute exacerbation of IPF (817.7 +/- 283.6 ng/ml, n = 3), and HP (716.6 +/- 548.8 ng/ml, n = 4) were significantly higher than those in the healthy elderly controls (p < 0.05), whereas those of pneumoconiosis, bronchiectasis, and bacterial pneumonia, 121.9 +/- 92.8 ng/ml (n = 8), 93.9 +/- 72.9 ng/ml (n = 11), and 72.7 +/- 3.4 ng/ml (n = 4), respectively, showed no significant difference with the controls. In active pulmonary TB, the percentage of patients whose serum SP-D levels were over 134.6 ng/ml (mean + 2SD of healthy elderly controls) was 34.7%, and therefore we considered the serum SP-D level was not useful for the diagnosis of pulmonary TB. However, it was significantly higher in the patients with cavity formation than in those without (p < 0.05), and there was a significant positive correlation between the serum SP-D level and the number of tubercle bacilli in the sputum (r = 0.416, p = 0.00165), erythrocyte sedimentation rate at 1 hr (r = 0.489, p < 0.01), and CRP level (r = 0.383, p = 0.003). These findings suggest that the serum SP-D level is a useful indicator of the disease activity in pulmonary TB.