Dendritic cell depletion and repopulation in the lung after irradiation and bone marrow transplantation in mice.

Dendritic cells (DCs) are essential for innate and adaptive immunity, but are purported to exhibit variable radiosensitivity in response to irradiation in various bone marrow transplantation (BMT) protocols. To address this controversy, we analyzed the magnitude of depletion and repopulation of both lung CD11b(pos) DC and CD103(pos) DC subsets in response to irradiation and BMT in a murine model. In our study, CD45.2(pos) donor bone marrow cells were transplanted into irradiated CD45.1(pos) recipient mice to examine the depletion of recipient DC subsets and the repopulation of donor DC subsets. We observed an apoptosis-mediated and necrosis-mediated depletion (> 90%) of the recipient CD103(pos) DC subset, and only a 50-60% depletion of recipient CD11b(pos) DCs from lung parenchymal tissue on Days 3 and 5, whereas recipient alveolar and lung macrophages were much less radiosensitive, showing an approximately 50% depletion by Days 14-21 after treatment. A repopulation of lung tissue with donor DC subsets had occurred by Days 10 and 28 for CD11b(pos) DCs and CD103(pos) DCs, whereas alveolar and lung macrophages were repopulated by 6 and 10 weeks after treatment. Furthermore, the infection of mice with Streptococcus pneumoniae further accelerated the turnover of lung DCs and lung macrophage subsets. Our data illustrate the vulnerability of lung CD103(pos) DCs and CD11b(pos) DCs to irradiation, and indicate that an accelerated turnover of lung DC subsets occurs, relative to pulmonary and lung macrophages. Our findings may have important implications in the development of adjuvant immune-stimulatory protocols that could reduce the risk of opportunistic infections in patients undergoing BMT.