The effect of pulmonary macrophage transplantation in the pulmonary fibrosis of mice

Abstract

[Background/Purpose] Recently, pulmonary macrophage (Mφ) transplantation(PMT) therapy for respiratory diseases has attracted much attention. In pulmonary fibrosis, pulmonary macrophages have been reported to be associated with both induction and suppression of fibrosis, and it is unclear whether PMT has a therapeutic effect. In this study, we examined the effect of PMT on bleomycin (BLM) induced pulmonary fibrosis in mice.

[Method] To prepare bone-marrow-derived macrophages (BMDMs), mononuclear cells were separated from bone marrow of C57BL/6 wild-type (Wt) mice by specific gravity centrifugation, and were cultured in vitro for 7 days in the presence of M-CSF and GM-CSF. In Wt-mice, BLM (2U/kg body weight) was instilled intratracheally to induce pulmonary fibrosis, in which BMDM (2×10⁶ cells) or PBS was intratracheally administered on day 7, and then fibrosis was analyzed on day 21.

[Results] The microscopic image showed that the cultured cells were large in size with small N/C ratio and renal nucleus shape. Flow cytometry analysis revealed that the cultured cells were CD45⁺/CD64⁺/CD11b⁺, which are consistent with the profile of Mφ. In addition, the BMDMs showed low expression of Ly6C, a marker of inflammatory function of Mφ, suggesting that the cells did not possess inflammatory traits. Histopathological scoring of lung fibrosis using modified Ashcroft scoring revealed a higher fibrosis score in the BMDMs-treated group compared to the PBS-treated group (BLM+BMDMs = 5.07 ± 0.55 vs. BLM+PBS = 4.20 ± 0.73, P < 0.05). The BMDM group showed worsening of pulmonary fibrosis than the PBS group.

[Conclusions] PMT during inflammatory phase may exacerbate the development of pulmonary fibrosis induced by BLM.