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01.12.2018 | Research | Ausgabe 1/2018 Open Access

Respiratory Research 1/2018

Fibrocytes are increased in lung and peripheral blood of patients with idiopathic pulmonary fibrosis

Respiratory Research > Ausgabe 1/2018
P. Heukels, J. A. C. van Hulst, M. van Nimwegen, C. E. Boorsma, B. N. Melgert, L. M. van den Toorn, K. A. T. Boomars, M. S. Wijsenbeek, H. Hoogsteden, J. H. von der Thüsen, R. W. Hendriks, M. Kool, B. van den Blink
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The online version of this article (https://​doi.​org/​10.​1186/​s12931-018-0798-8) contains supplementary material, which is available to authorized users.



Fibrocytes are implicated in Idiopathic Pulmonary Fibrosis (IPF) pathogenesis and increased proportions in the circulation are associated with poor prognosis. Upon tissue injury, fibrocytes migrate to the affected organ. In IPF patients, circulating fibrocytes are increased especially during exacerbations, however fibrocytes in the lungs have not been examined.
Therefore, we sought to evaluate if fibrocytes can be detected in IPF lungs and we compare percentages and phenotypic characteristics of lung fibrocytes with circulating fibrocytes in IPF.


First we optimized flow cytometric detection circulating fibrocytes using a unique combination of intra- and extra-cellular markers to establish a solid gating strategy. Next we analyzed lung fibrocytes in single cell suspensions of explanted IPF and control lungs and compared characteristics and numbers with circulating fibrocytes of IPF.


Using a gating strategy for both circulating and lung fibrocytes, which excludes potentially contaminating cell populations (e.g. neutrophils and different leukocyte subsets), we show that patients with IPF have increased proportions of fibrocytes, not only in the circulation, but also in explanted end-stage IPF lungs. These lung fibrocytes have increased surface expression of HLA-DR, increased intracellular collagen-1 expression, and also altered forward and side scatter characteristics compared with their circulating counterparts.


These findings demonstrate that lung fibrocytes in IPF patients can be quantified and characterized by flow cytometry. Lung fibrocytes have different characteristics than circulating fibrocytes and represent an intermediate cell population between circulating fibrocytes and lung fibroblast. Therefore, more insight in their phenotype might lead to specific therapeutic targeting in fibrotic lung diseases.
Additional file 2: Sort strategy for CD45+/Col-1+ cells. (A) The conventional strategy with the CD45+/Col-1+ cells in red. (B) Position of the same fibrocytes when employing a gating strategy based on additional extracellular markers. The sort strategy is based on extracellular markers and with some modifications previously published [16] (of note: for our research question we did not exclude SSChi cells). CD45+ cells were analyzed for HLA-DR expression and lineage markers to exclude B-cells (CD19), NK cells (CD56) and T-cells (CD3). Lineage negative cells were plotted as CD14 versus CD16 to create a distinct group of cells enriched for CD45+/Col-1+ cells (red box). (PDF 75 kb)
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