Depletion of bronchus-associated lymphoid tissue associated with lung allograft rejection.

Pulmonary infections remain one of the major complications of lung transplantation. The bronchus-associated lymphoid tissue (BALT) forms a local immune system that normally protects the lung from infection. The effects of lung transplantation and lung allograft rejection on the BALT were examined using immunoperoxidase techniques. The BALT was evaluated by quantifying the number of immunoglobulin-bearing plasma cells in the lamina propria of sections of trachea and mainstem bronchus. Sections of donor mainstem bronchus from 2 patients with allograft rejection were compared with sections of native trachea from these same patients, and with sections of mainstem bronchus from 2 transplanted lungs without rejection and 20 controls. Lung allografts from the 2 patients with rejection had a marked depletion of submucosal IgA-bearing and IgG-bearing plasma cells. Two sets of transplanted lungs without evidence of rejection showed only a mild reduction of the BALT. The depletion of BALT associated with allograft rejection may contribute to the increased incidence of pulmonary infections seen in these patients.