Clinical significance of serum KL-6 in pulmonary sarcoidosis

We investigated whether the level of serum KL-6 could be an activity marker for pulmonary sarcoidosis. In 33 patients with pulmonary sarcoidosis, the relationships between serum KL-6 levels and diagnostic imaging, serum angiotensin-converting enzyme (ACE) levels, serum lysozyme levels, steroid therapy, and prognosis were evaluated. There were no significant differences in the level of serum KL-6 when the patients were divided on the basis of radiographic findings, but the level of serum KL-6 was markedly elevated in some patients with stage-II pulmonary sarcoidosis. There was a significant correlation between serum KL-6 levels and the following two parameters: serum ACE and lysozyme levels. Among patients with a high initial level of serum KL-6, pulmonary sarcoidosis tended to become exacerbated within one year. Steroid therapy significantly decreased the level of serum KL-6, suggesting that the level of serum KL-6 could be an activity indicator for pulmonary sarcoidosis. Immunohistochemical staining by anti-KL-6 antibody revealed that KL-6 was localized in proliferating type-II alveolar epithelial cells.