Abstract
Macrophages play a key role in the innate immune system. Macrophages are thought to originate from hematopoietic precursors or the yolk sac. Here, we describe the in vitro establishment of self-renewable GM-CSF-dependent immature macrophages (GM-IMs) from murine bone marrow (BM). GM-IMs grow continuously in vitro in conditioned medium containing GM-CSF. The immunophenotype of GM-IMs is F4/80high CD11bhigh CD11clow Ly6Clow. By comparing gene expression in GM-IMs and BM dendritic cells, we found that GM-IMs expressed lower levels of chemokines, cytokines and their receptors. GM-IMs are round in shape, attach loosely to non-coated culture dishes and have a marked phagocytic capacity. These results indicate that GM-IMs are macrophage precursor cells. Following stimulation with LPS, monocyte-like GM-IMs converted to flat macrophage-like cells that tightly adhered to non-coated culture dishes and produced pro-inflammatory cytokines TNFα, IL-6 and IL-1β. These results indicated that GM-IMs differentiated to M1 pro-inflammatory macrophages. This was confirmed by stimulation of GM-IMs with IFNγ, an inducer of M1 markers. GM-IMs showed enhanced expression of M2 macrophage markers such as Arg1 and Retnla following stimulation by Th2 cytokines IL-4 and IL-13. When GM-IMs were injected into mice at sites of wounding, wound repair was enhanced. These results indicate that GM-IMs can differentiate to M2 macrophages. When GM-IMs were injected into clodronate-treated mice, they induced resident macrophage proliferation by producing M-CSF. In conclusion we have established self-renewable GM-CSF-dependent immature macrophages in vitro from murine BM, which differentiate to M1 or M2 macrophages.
Highlights
Macrophages and dendritic cells (DCs) are present in all tissues and are crucial for immune and inflammatory responses
Because GM-CSF-dependent immature macrophages (GM-IMs) can self-renew in the presence of GM-CSF, we propose that the same myeloid population might exist in vivo
We suggest that GM-CSF continuously produced in vivo could support a small population of myeloid lineage cells that self-renews
Summary
Macrophages and dendritic cells (DCs) are present in all tissues and are crucial for immune and inflammatory responses. Hematopoietic stem cells (HSCs) give rise to most macrophages and they are replaced continually by macrophage and DC precursors [4,5]. All resident macrophages in tissues may be derived from circulating monocytes [2] This model of the development of the MPS has been challenged recently. Furth et al showed the dual origin of tissue macrophages by labeling monocytes from BM with [3H]thymidine. It was shown that YS-derived F4/80 bright macrophages are present in several tissues of adult mice and are distinct from HSC progeny [12]. GM-IMs could differentiate to M1 or M2 macrophage subpopulations
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
