Table 1

Evidence for, and against, circulating progenitor cell generation of non-hematopoietic lung cell types.
Study Type	Disease or Model	Tissue of Origin	Lung Cell Type Formed / Frequency	Method of Detection	Ref.

Animal, in-vivo	BMT	MSC	Undefined mesenchymal cells / occasional	PCR for collagen gene marker	[30]
Animal, in-vivo	Bleomycin fibrosis	MSC	Type I pneumocytes / rare	β galactosidase protein	[23]
Animal, in-vivo	BMT	HSC enrichment	Type II pneumocytes / up to 20%, bronchial epithelium / 4%	Y chromosome FISH, surfactant B mRNA	[31]
Animal, in-vivo	Radiation pneumonitis	Whole bone marrow	Type II pneumocytes, bronchial epithelium / up to 20% of type II cells	Y chromosome FISH, surfactant B mRNA	[25]
Animal, in-vivo	BMT	Whole bone marrow/EGFP retrovirus	Type II pneumocytes / 1–7%	EGFP, keratin immunostain, surfactant protein B FISH	[33]
Animal, in-vivo	BMT and parabiotic animals	HSC	Hematopoietic chimerism but exceedingly rare lung cell types	EGFP	[32]
Animal, in-vivo	Bleomycin fibrosis	MSC	Type II pneumocytes / ~1%	Y chromosome FISH	[22]
Animal, in-vivo	Radiation fibrosis	MSC or whole bone marrow	Fibroblasts / common	EGFP, Y chromosome FISH, vimentin immunostain	[26]
Animal, in-vivo	BMT	Bone marrow, EGFP labeled	Fibroblasts, Type I pneumocyte / occasional to rare	Flow cytometry	[34]
Animal, in-vitro and in-vivo	Hypoxia-induced pulmonary hypertension	Circulating BM-derived c-kit positive	c-kit positive cells in pulmonary artery vessel wall; In hypoxia, circulating cells generate endothelial and smooth muscle cells in-vitro	Flow cytometry and immunohistochemistry	[27]
Animal, in-vivo	Ablative radiation and elastase induced emphysema	GFP + fetal liver	Alveolar epithelium and endothelium; frequency not reported but increased by G-CSF and retinoic acid	Immunohistochemistry for CD45^-, GFP⁺cells	[28]
Animal, in-vivo	Bleomycin fibrosis	Whole marrow GFP⁺	GFP⁺type I collagen expressing	Flow cytometry and immunohistochemistry, RT-PCR	[24]
Human, in-vitro	Heat shock in cell culture	MSC and SAEC	Cell fusion / common	Immunostaining, microarray	[39]
Animal, in-vivo Human, in-vivo	OVA-sensitized mouse model Allergen – sensitized asthmatics	CD34 positive, collagen I expressing fibrocytes CD34 positive, collagen I expressing fibrocytes	Myofibroblasts / ? Myofibroblasts / ?	CD34-positive, collagen I, α-smooth muscle actin CD34-positive, collagen I, α-smooth muscle actin	[29]
Human, in-vivo	Human heart and lung transplant	Sex-mismatched donor lung or heart	No lung cell types of recipient origin	X and Y chromosome FISH, antibody stain for hematopoeitic cells	[36]
Human, in-vivo	Human lung transplant Human BMT	Sex-mismatched donor lung Sex-mismatched donor bone marrow	Bronchial epithelium, type II pneumocytes, glands of recipient origin / 9 – 24% No lung cell types of donor origin	Y chromosome FISH, short tandem repeat PCR Y chromosome FISH, short tandem repeat PCR	[35]
Human, in-vivo	Human BMT	Sex-mismatched donor bone marrow	Lung epithelium and endothelium of donor origin / up to 43%	X and Y chromosome FISH, keratin and PECAM immunostain	[38]
Human, in-vivo	Human BMT	Sex-mismatched donor bone marrow	No nasal epithelium of donor origin	Y chromosome FISH, cytokeratin immunostain	[37]

BMT = bone marrow transplant (with prior ablation), MSC = mesenchymal stem cells (bone marrow stromal cells, adherent bone marrow cells), EGFP = enhanced green fluorescent protein, HSC = hematopoietic stem cells, FISH = fluoresence in situ hybridization, SAEC = small airway epithelial cells
Neuringer and Randell Respiratory Research 2004 5:6 doi:10.1186/1465-9921-5-6