PURPOSE: KL-6 is a glycoprotein expressed on type 2 pneumocytes and respiratory bronchiolar epithelial cells. Serum KL-6 levels have been shown to be elevated in various interstitial lung diseases and correlate with disease activity. We previously reported that serum KL-6 levels were elevated in lung transplant recipients with chronic airway rejection [bronchiolitis obliterans syndrome (BOS)], when compared to recipients who did not have this complication. We therefore concluded that serum KL-6 levels could be used as a diagnostic tool for non-invasive detection of BOS. The drop in lung function that can occur with acute rejection episodes can confound the diagnosis of BOS. Thus, a need to evaluate how serum KL-6 levels would change during acute rejection episodes has emerged. The pathology of acute rejection occurs predominantly around the blood vessels without involvement of the airways or the alveoli where KL-6 is localized. Therefore, we hypothesized that serum KL-6 levels would not be elevated during episodes of acute rejection in lung transplant recipients.
METHODS: To test our hypothesis, we collected blood samples from patients undergoing transbronchial lung biopsy (TBB) for surveillance and measured serum KL-6 levels by ELISA. Lung transplant recipients who had BOS or other conditions known to cause elevations of KL-6 were excluded. Mean (±SD) KL-6 levels were calculated for biopsies without rejection and were compared with means for biopsies showing different grades of rejection by using T-test.
RESULTS: A total of 68 samples were collected from 34 patients. The mean serum KL-6 for biopsies without rejection (A0) was 260±129 U/mL, while levels for A1 and A2+A3 rejections were 218±79 U/mL and 231±91 U/mL, respectively. There were no statistically significant differences between the A0 group and any of the other 2 groups (p>0.1 for both comparisons).
CONCLUSION: Our results indicate that serum KL-6 levels do not elevate with episodes of acute vascular rejection in lung transplant recipients.
CLINICAL IMPLICATIONS: Thus, serum KL-6 carries the potential to be a specific test for screening of chronic airway rejection.
DISCLOSURE: Minh Doan, None.