Recruitment of donor effector cells to the lungs after BMT. Donor T cells and monocytes/macrophages are recruited to the lung and cause lung injury after allogeneic BMT. B6D2F₁ mice received allogeneic (▪) or syngeneic (□) BM transplants, and lungs were examined at weeks 1, 2, 4, and 6 as described in “Patients, materials, and methods.” Photomicrographs (original magnification, × 200) from hematoxylin-eosin–stained sections obtained 6 weeks after syngeneic (panel A) or allogeneic (panel B) BMT. Recipients of allogeneic BM transplants develop significant lung pathology compared with syngeneic controls as determined with a semiquantitative scoring system (panel C). Total BAL fluid cellularity (panel D) and T-cell counts (panel E) correlate with histologic changes. Data are from 2 experiments representative of 3 and are presented as mean ± SEM; n = 8 to 10 per group per time point; ^*P < .01.