Thioredoxin as a biomarker for graft rejection in lung transplant recipients

Primary graft dysfunction and rejection are common complications in lung transplant recipients. Increased expression of thioredoxin-1 (Trx), a 12-kDa redox-regulatory protein, has been reported in multiple lung pathophysiological conditions involving oxidative and inflammatory mediated injury including graft rejection in canine and rat models of lung transplantation. Our objective was to determine whether increased Trx expression is associated with progression of rejection pathophysiology in human lung transplant recipients. Bronchoalveolar lavage (BAL) fluid and transbronchial biopsy samples were collected as a routine part of post-transplant clinical care from 18 lung transplant patients from our adult lung transplant programme. Lung transplant recipient profile included age/sex, ethnic background, days on ventilator, total ischaemic time, and cytomegalovirus (CMV) status. Based on histopathological grading criteria, patients were divided into two groups, rejecting (A1/A2 or B1) and non-rejecting (A0/B0). Rejecting and non-rejecting group total BAL cell counts and differential cell counts for neutrophils, macrophages, lymphocytes and eosinophils as well as total BAL cell Trx levels were analysed. Total BAL cell counts were significantly (p < 0.05) elevated in graft rejecting versus non-rejecting patients. Differential BAL macrophage counts were comparable in rejection and non-rejection groups, whereas there were significant increases in neutrophils and lymphocytes but not eosinophils in patients with rejection versus non-rejection pathology (p < 0.05). Total ischaemic time and days on ventilator in rejection and non-rejection groups were comparable. However, Trx levels were significantly elevated in BAL cells from graft-rejecting patients compared with non-rejecting patients (p < 0.05). These data suggest that surveillance monitoring of BAL Trx levels after lung transplantation can serve as a biomarker to assess severity of graft rejection.