Identification of Ki67+ 'monocytic' cells within the lungs

Rationale: Alveolar macrophages (AM) are considered to be mainly derived from non-proliferating, CX 3 CR1 + Ki67 - blood monocytes. Expression of cell-cycle maintaining protein Ki67 has however been observed on 9monocyte-like9 cells in bronchoalveolar lavage fluid. A rare CD34 + blood monocyte is known to express Ki67. Aim: To identify CX 3 CR1 + Ki67 + cells within the lungs Methods: Lung tissue was obtained from COPD patients (n=9), smokers (S) (n=9) and healthy non-smokers (HNS) (n=6) undergoing surgical resection of lung carcinoma. Ki67 was detected by immunohistochemistry (MIB1 and SP6 clones). Ki67 + cells underwent immunophenotyping for expression of CD45, CX 3 CR1, CD3 (lymphocyte marker), CD34 (immature bone marrow cell marker) and neutrophil elastase (NE). Each section was fully imaged; 10 vessels per section were selected at random for analysis of cells apposed to endothelium (marginated) and those present in the central column (luminal). Results: Ki67 + cells were present within the pulmonary micro-vessels and alveoli of COPD, S u0026 HNS. These cells expressed pan-leucocyte marker CD45 and mononuclear cell marker CX 3 CR1 + but not CD34, CD3 or NE, which suggests that they were monocytes. There were no differences in the proportion of marginated (mean% 71 vs 69.3 vs 87; COPD vs S vs HNS respectively, ANOVA pu003e0.05) or luminal (mean% 60 vs 61 vs 53; COPD vs S vs HNS, ANOVA pu003e0.05) Ki67 + intravascular cells. HNS had a significantly higher proportion of alveolar Ki67 + cells compared to COPD (p Conclusion: We describe a novel population of CD45 + CX 3 CR1 + Ki67 + CD34 - 9monocytic9 cells present within the lungs which may contribute towards AM homeostasis.