β2 Integrins Regulate Migratory Properties of M1 and M2 Macrophages during Inflammation

Abstract

BackgroundThe development of chronic inflammation depends on the balance between accumulation of pro‐inflammatory, classically activated (M1) and alternatively activated (M2) macrophages within the injured tissue. The mesenchymal migration and accumulation of macrophages in the inflamed sites largely depend on myeloid‐specific αMβ2 and αDβ2 integrins, which share similar ligands but have different densities on different subsets of macrophages. The level of integrin expression regulates cell migration. Namely, a low‐intermediate expression supports cell motility, while a high expression generates strong adhesion that prevents cell migration. In this project, we tested how αMβ2 and αDβ2 integrins are involved in the migration and retention of M1 and M2 macrophages at the site of inflammation.Method and ResultsTo test our hypothesis, wild type (WT), αD−/− and αM−/− mice were intraperitoneally injected with thioglycollate to generate macrophages. Isolated macrophages were treated with IFN‐γ and IL‐4 for 4 days to activate M1 and M2 phenotypes, respectively. Integrin levels on macrophages were evaluated by qPCR and FACS. We found that the expression of αD was strongly upregulated on M1 macrophages, but not on M2 macrophages, while the level of αM remained unchanged on both subsets. To test the effect of integrins on the migration of M1 and M2 macrophages, we labeled cells with red and green fluorescent dyes and applied in vitro migration assay in 3D fibrin matrix.Our results showed that WT M2 macrophages possess significantly stronger migratory properties compared to WT M1 macrophages. To understand the contribution of individual integrins we used αD−/− and αM−/− macrophages. The results demonstrated that while αM‐deficiency had no significant effect, αD‐deficiency improved the migration of M1 macrophages. In contrast, both αD‐ and αM‐deficiency reduced the migration of M2 macrophages. To verify these results, we tested in vivo macrophage migration using the model of resolution of peritoneal inflammation. M1 and M2 macrophages, labeled with red and green fluorescent dyes respectively, were injected into the peritoneal cavity of mice with induced peritoneal inflammation. After 3 days, we evaluated the ability of macrophages to emigrate from the peritoneal cavity to lymphatics. Our results corresponded to our in vitro migratory assay. M2 macrophages emigrate significantly faster, αD‐deficiency improves the efflux of M1 macrophages and αD‐ and αM‐deficiency reduced the emigration of M2 macrophages.ConclusionTaken together, these data suggest that integrin αM, which has an intermediate expression on M1 and M2 macrophages, supports macrophage migration. In contrast, integrin αD, which has a high expression on M1 macrophages, prevents the migration of these cells and can promote the retention of M1 macrophages in the inflamed sites. Therefore, integrin αD is a potential therapeutic target to prevent pro‐inflammatory macrophage accumulation and development of chronic inflammation.Support or Funding InformationThis project is funded by NIH and the project number is 5R01DK102020‐05This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.