Characterization of murine monocyte and macrophage subsets in immune-mediated hepatitis

Introduction Monocyte and macrophage populations have been classified into pro-inflammatory M1 and anti-inflammatory/restorative M2 subsets based on expression of Ly6C^hi/CCR2 and Ly6C^int/low/CX₃CR1, respectively. However, whether these so defined M1 and M2 subsets particularly express genes associated with pro- or anti-inflammatory/restorative function in liver disease is not clear. Therefore, we aimed at analysing the gene expression profile of hepatic monocyte and macrophage subsets in immune-mediated acute and chronic liver inflammation.

Methods To induce acute liver injury, C57BL/6 mice received ConA and were analysed 8 h later. Mdr2 ^-/- mice were used as a model of chronic liver inflammation. The PrimeFlow RNA assay was used for simultaneous analysis of mRNA and protein expression by flow cytometry.

Results In acute liver inflammation, the frequencies of Ly6C^hi monocytes and macrophages as well as Ly6C^int macrophages were increased. We determined high expression of CX₃CR1 by Ly6C^hi monocytes and macrophages. Ly6C^int macrophages were also characterized by expression of CX₃CR1, however, the frequency of CX₃CR1⁺ Ly6C^int macrophages was decreased compared to the Ly6C^hi counterparts. Interestingly, gene expression profiling revealed an enhanced expression of both, genes associated with pro-inflammatory (Tnf, Nos2, Il6) and anti-inflammatory/restorative function (Il10, Arg1, Chil3, Tgfb1) in Ly6C^hi monocytes and macrophages while Ly6C^int macrophages were predominantly characterized by expression of genes associated with anti-inflammatory/regenerative function (Il10, Chil3, Areg, Mmp9). In 12 weeks old Mdr2 ^-/- mice, the frequencies of Ly6C^int and Ly6C^low macrophages were increased while the frequency of Ly6C^hi monocytes was decreased. The frequencies of CX₃CR1⁺ Ly6C^low macrophages and Ly6C^hi monocytes were elevated. Ly6C^int and Ly6C^low macrophages showed elevated expression of genes associated with pro-inflammatory (Nos2, Il6) and anti-inflammatory/restorative function (Il10, Chil3, Areg). Moreover, Il12b and Il10 gene expression were up-regulated in all monocyte subsets.

Conclusion Chemokine receptor and gene expression analysis revealed that particularly the classical M1 phenotype characterization based on expression of Ly6C^hi/CCR2 is not appropriate for hepatic monocyte and macrophage subsets, which are characterized by high expression of CX₃CR1 and genes associated with both, pro- and anti-inflammatory/restorative function in liver injury.

Publikationsverlauf

Artikel online veröffentlicht:
04. Januar 2021