Histologic changes in donor bronchi may explain the reduced mucosal blood flow seen during acute lung allograft rejection.

We assessed the histologic changes in donor and recipient bronchi from 15 dogs that had received a lung transplant and related these changes to the severity of acute rejection seen in the parenchyma of these same lungs. Minimal rejection was associated with no abnormal change in either the donor or the recipient bronchi. In mild lung rejection, mononuclear cell cuffings were seen around bronchial arteries in donor bronchial adventitia, although few mononuclear cell infiltrates were seen in the submucosa. Moderate lung rejection was associated with more prominent mononuclear cell cuffings in the donor bronchial adventitia and mucosal infiltrates of mononuclear cells in the membranous portion. In cases of severe lung rejection, the mononuclear cell infiltrates were also apparent in the cartilaginous portion of the donor bronchial mucosa. Moreover, submucosal edema and detachment of bronchial epithelium were seen. These histologic changes were not observed in the recipient bronchi during acute rejection, nor were they seen in the donor and the recipient bronchi during lung infection without rejection. They might, therefore, reflect acute rejection in the donor bronchus. These results might provide the histologic support for our previous observation of decreased bronchial mucosal blood flow measured by the laser Doppler flowmeter in relation with the extent of acute lung rejection.