Fibroblasts of recipient origin contribute to bronchiolitis obliterans in human lung transplants.

Rationale: The participation of circulating precursor cells in the development of experimental pulmonary fibrosing lesions in mice has been recently demonstrated.Objectives: This study analyzes whether circulating, bone marrow–derived, fibroblastic precursor cells contribute to the development of fibrosing lesions in human lungs, especially bronchiolitis obliterans.Methods: The occurrence of in situ microchimerism in bronchiolitis obliterans lesions of human lung allografts (n = 12) as well as of autologous lung tissue from patients post–bone marrow transplantation (n = 2) was analyzed using laser-assisted microdissection after immunohistochemical labeling of leukocytes followed by short tandem repeat–polymerase chain reaction–based genotyping. Combined immunofluorescence and fluorescence in situ hybridization for sex chromosomes was performed for independent confirmation in cases with appropriate sex mismatch (n = 2).Measurements and Main Results: The bronchiolitis obliterans lesions of all 12 lung trans...