THE ORIGIN OF ALVEOLAR MACROPHAGES IN THE TRANSPLANTED LUNG

Transplanted lungs are initially populated by donor pulmonary alveolar macrophages (PAMs). These will form major antigen presenters for the recipient's suppressed immune system. They may be expected to be replaced by recipient major histocompatibility complex-compatible cells, with time. We have isolated CD14+ PAMs from bronchoalveolar lavage specimens for 6 months after transplantation and identified their origin by using microsatellite analysis. This DNA-based technology permits the reliable identification of the origin of cells from different individuals. We show that replacement of donor PAMs occurs with individual dynamics in each case. Recipient PAMs usually appeared within 2 weeks, whereas donor cells could be retained for as long as 6 months. In this limited series, there was no obvious correlation between the dynamics of this process and the occurrence of rejection episodes or infections.