Conclusion
Our findings suggest that M2 Mϕ following IVD injury may originate from resident Mϕ. TGF-β is a key factor for M2 polarization of macrophages following IVD injury.
Methods
To investigate the origin of M2 macrophages, 30 GFP chimeric mice were created by bone marrow transplantation. IVDs were obtained from both groups on pre-puncture (control) and post-puncture days 1, 3, 7, and 14 and CD86 (M1 marker)- and CD206 (M2 marker)-positive cells evaluated by flow cytometry (n = 5 at each time point). To investigate the role of TGF-β on M2 polarization, TGF-β inhibitor (SB431542) was also injected on post-puncture days (PPD) 5 and 6 and CD206 expression was evaluated on day 7 by flow cytometry (n = 5) and real time PCR (n = 10).
Results
The proportion of CD86+ Mϕ within the GFP+ population was significantly increased at PPD 1, 3, 7, and 14 compared to control. CD206-positive cells in GFP-populations were significantly increased on PPD 7 and 14. In addition, the percentage of CD206-positive cells was significantly higher in GFP-populations than in GFP+ populations. TGF-β inhibitor reduced CD206-positive cells and Cd206 expression at 7 days after puncture.