Abstract
Macrophages play a key role in host defense against microbes, in part, through phagocytosis. Macrophage receptor with collagenous structure (MARCO) is a scavenger receptor on the cell surface of macrophages that mediates opsonin-independent phagocytosis. The goal of our study is to investigate the role of MARCO in LPS or lipotechoic acid–induced macrophage tolerance. Although it has been established that expression of MARCO and phagocytosis is increased in tolerant macrophages, the transcriptional regulation and biological role of MARCO in tolerant macrophages have not been investigated. In this study, we confirm that tolerized mouse bone marrow–derived macrophages (BMDM) selectively increase expression of MARCO (both transcript and cell surface receptor) and increase phagocytosis. We found that H3K4me3 dynamic modification of a promoter site of MARCO was increased in tolerized BMDM. Blocking methylation by treatment with 5-aza-2′-deoxycytidine resulted in reduced H3K4me3 binding in the promoter of MARCO, decreased expression of MARCO, and impaired phagocytosis in tolerized BMDM. However, 5-aza-2′-deoxycytidine had no effect on the inflammatory component of innate immune tolerance. In aggregate, we found that histone methylation was critical to MARCO expression and phagocytosis in tolerized macrophages, but did not affect the inflammatory component of innate immune tolerance.
Footnotes
This work was supported in part by National Institutes of Health Grants R01-HL095393, P01-ES18181, and RC2-HL101715.
The online version of this article contains supplemental material.
Abbreviations used in this article:
- 5-AZA
- 5-aza-2′-deoxycytidine
- BMDM
- bone marrow–derived macrophage
- ChIP
- chromatin immunoprecipitation
- EU
- endotoxin unit
- LTA
- lipoteichoic acid
- MARCO
- macrophage receptor with collagenous structure
- qPCR
- quantitative PCR
- RT
- room temperature
- WT
- wild-type.
- Received October 24, 2012.
- Accepted April 4, 2013.
- Copyright © 2013 by The American Association of Immunologists, Inc.