The origin of alveolar macrophages in the transplanted lung - A longitudinal microsatellite-based study of donor and recipient DNA

Transplanted lungs are initially populated by donor pulmonary alveolar macr ophages (PAMs). These will form major antigen presenters for the recipient' s suppressed immune system. They may be expected to be replaced by recipien t major histocompatibility complex-compatible cells, with time. We have iso lated CD14+ PAMs from bronchoalveolar lavage specimens for 6 months after t ransplantation and identified their origin by using microsatellite analysis . This DNA-based technology permits the reliable identification of the orig in of cells from different individuals. We show that replacement of donor P AMs occurs with individual dynamics in each case. Recipient PAMs usually ap peared 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 i nfections.