Sequestration and homing of bone marrow-derived lineage negative progenitor cells in the lung during pneumococcal pneumonia

Bone marrow (BM)-derived progenitor cells have been shown to have the potential to differentiate into a diversity of cell types involved in tissue repair. The characteristics of these progenitor cells in pneumonia lung is unknown. We have previously shown that Streptococcus pneumoniae induces a strong stimulus for the release of leukocytes from the BM and these leukocytes preferentially sequester in the lung capillaries. Here we report the behavior of BM-derived lineage negative progenitor cells (Lin- PCs) during pneumococcal pneumonia using quantum dots (QDs), nanocrystal fluorescent probes as a cell-tracking technique.

In this study, we demonstrated that BM-derived progenitor cells are preferentially sequestered and retained in pneumonic mouse lungs. These cells potentially contribute to the repair of damaged lung tissue.

Whole BM cells or purified Lin- PCs, harvested from C57/BL6 mice, were labeled with QDs and intravenously transfused into pneumonia mice infected by intratracheal instillation of Streptococcus pneumoniae. Saline was instilled for control. The recipients were sacrificed 2 and 24 hours following infusion and QD-positive cells retained in the circulation, BM and lungs were quantified.

Pneumonia prolonged the clearance of Lin- PCs from the circulation compared with control (21.7 +/- 2.7% vs. 7.7 +/- 0.9%, at 2 hours, P < 0.01), caused preferential sequestration of Lin- PCs in the lung microvessels (43.3 +/- 8.6% vs. 11.2 +/- 3.9%, at 2 hours, P < 0.05), and homing of these cells to both the lung (15.1 +/- 3.6% vs. 2.4 +/- 1.2%, at 24 hours, P < 0.05) and BM as compared to control (18.5 +/- 0.8% vs. 9.5 +/- 0.4%, at 24 hours, P < 0.01). Very few Lin- PCs migrated into air spaces.