Characterization, localization and comparison of c-Kit plus lung cells in never smokers and smokers with and without COPD

Background: c-Kit + lung stem cells have been described in the human healthy lung. Their potential relation with smoking and/or chronic obstructive pulmonary disease (COPD) is unknown. Methods: We characterized and compared c-Kit+ cells in lung tissue of 12 never smokers (NS), 15 smokers with normal spirometry (S) and 44 COPD patients who required lung resectional surgery. Flow cytometry (FACS) was used to characterize c-Kit+ cells in fresh lung tissue disaggregates, and immunofluorescence (IF) for further characterization and to determine their location in OCT-embedded lung tissue. Results: We identified 4 c-Kit+ cell populations, with similar proportions in NS, S and COPD: (1) By FACS, c-Kit(high)/CD45 + cells (4.03 +/- 2.97% (NS), 3.96 +/- 530% (5), and 5.20 +/- 3.44% (COPD)). By IF, these cells were tryptase+ (hence, mast cells) and located around the airways; (2) By IF, c-Kit(low)/CD45+/triptase- (0.07 +/- 0.06 (NS), 0.03 +/- 0.02 (5), and 0.06 +/- 0.07 (COPD) cells/field), which likely correspond to innate lymphoid cells; (3) By FACS, c-Kit(low)/CD45-/CD34+ (0.95 +/- 0.84% (NS), 1.14 +/- 0.94% (S) and 0.95 +/- 138% (COPD)). By IF these cells were c-Kit(low)/CD45-/CD31+, suggesting an endothelial lineage, and were predominantly located in the alveolar wall; and, (4) by FACS, an infrequent c-Kit(low)/CD45-/ CD34-population (0.09 +/- 0.14% (NS), 0.08 +/- 0.09% (S) and 0.08 +/- 0.11% (COPD)) compatible with a putative lung stem cell population. Yet, IF failed to detect them and we could not isolate or grow them, thus questioning the existence of c-Kit+ lung stem-cells. Conclusions: The adult human lung contains a mixture of c-Kit+ cells, unlikely to be lung stem cells, which are independent of smoking status and/or presence of COPD.