Background/Purpose: In bleomycin-induced model of systemic fibrosis and patients with systemic sclerosis, plasmacytoid DC (pDC) are unaffected or reduced systemically (spleen/peripheral blood) but they increase in the lungs (Kafaja S, et al, JCI Insight 2018). Depletion of pDCs ameliorated fibrosis in the bleomycin model and altered the expression levels of proteins and genes implicated in chemotaxis, inflammation, and fibrosis in the lungs. In resonance with animal findings, the frequency of pDCs in the lungs of patients with SSc correlated with the severity of lung disease. Treatment with a tyrosine kinase inhibitor imatinib that has been reported to reduce and/or prevent deterioration of skin and lung fibrosis profoundly reduced pDCs in lungs but not in peripheral blood of patients with systemic sclerosis. In patients with systemic sclerosis, the frequency of pDCs also correlated with levels of proteins implicated in inflammation, vasculopathy and fibrosis. It is unclear if pDCs directly contribute to inflammatory and profibrotic milieu in the development of systemic fibrosis. Here, we asked if pDCs as compared to other immune cells contribute to proteins that are differentially expressed in the lungs after bleomycin exposure.

Methods: Female C57Bl/6 mice were injected with bleomycin (4 U/kg body weight) subcutaneously daily for 2 weeks. Lungs were harvested from bleomycin or control PBS injected animals on day 28. Lung extracts were analyzed for proteins by Western blot and ELISA, and freshly isolated single cells were analyzed for the expression of proteins on pDCs, myeloid dendritic cells (CD11c⁺CD11b⁺; mDC), other myeloid cells (CD11b⁺CD11c^–, monocyte/macrophages and neutrophils), B cells, and T cells by multiparameter flow cytometry. Relative expression of proteins was expressed as the ratio of the mean fluorescent intensity of cells stained with respective antibodies and isotype controls.

Results: Scavenger receptor CD36 that is implicated in platelet-collagen adhesion, oxidative stress and inflammation was significantly increased on pDCs (p <0.01) but not on mDCs, other myeloid cells, B cells and T cells in the lungs of bleomycin-injected animals as compared to control animals. TLR7 was also increased more on pDCs than on all other immune cells examined, whereas TLR2 was increased more on mDCs and other myeloid cells but not significantly on pDCs and B cells in the lungs of bleomycin-injected animals as compared to control animals. TGFβ latent peptide was higher on the surface of all immune cells examined in the lungs of bleomycin-injected animals than in control lungs. Among chemokine receptors examined, CCR2, CCR3, CCR6, CCR9 and CXCR4 were higher on pDCs than most other cells examined. CCR2 and CCR9 were also higher on mDCs, and CXCR4 was higher on B cells and mDCs in the lungs of bleomycin-injected animals as compared to control animals.

Conclusion: Our data suggest an important role of pDCs in eliciting pro-inflammatory and profibrotic milieu in the development of systemic fibrosis. These observations along with recently published studies identify the increased trafficking of pDCs to the affected organs as a potential therapeutic target in systemic sclerosis and other fibrotic diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/plasmacytoid-dendritic-cells-that-infiltrate-the-lungs-produce-profibrotic-cytokines-and-chemokines-in-bleomycin-induced-model-of-systemic-sclerosis/