Bronchial epithelial cell B7-1 and B7-2 mRNA expression after lung transplantation: a role in allograft rejection?

Obliterative bronchiolitis is commonly interpreted as chronic rejection and involves the bronchial and bronchiolar epithelium. Upregulation of major histocompatibility complex (MHC) II on bronchial epithelial cells (BEC) had been hypothesised to be an important trigger of a bronchus directed rejection response. More recently, the additional expression of the costimulatory molecules B7-1 (CD80) and B7-2 (CD86) on antigen presenting cells were found to play an important role in the activation of T-lymphocytes in transplant rejection. The role of the expression of these molecules by BEC is unclear. BEC obtained by bronchial brushing and bronchoalveolar lavage fluid (BALF) cells from lung transplant recipients were studied and evaluated for messenger ribonucleic acid (mRNA) expression of B7-1 and B7-2 by semi-quantitative reverse transcriptase-polymerase chain reaction. Significantly elevated B7-1/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA ratios were found in BEC from patients examined during the first 3 months after lung transplantation. Interestingly, in a small group of patients with bronchiolitis obliterans syndrome the B7-1/GAPDH and B7-2/GAPDH ratios were significantly elevated for BEC, whereas no differences were found for the BALF cells. In summary, B7 messenger ribonucleic acid expression by bronchial epithelial cells may play a role in (chronic) lung allograft rejection.