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Antimicrobial proteins of murine macrophages
P S Hiemstra1, P B Eisenhauer, S S Harwig
1Department of Infectious Diseases, University Hospital Leiden, The Netherlands.
Abstract:
Three murine microbicidal proteins (MUMPs) were purified from cells of the murine macrophage cell line RAW264.7 that had been activated by gamma interferon. Similar proteins were also present in nonactivated RAW264.7 cells, in cells of the murine macrophage cell line J774A.1, and in resident and activated murine peritoneal macrophages. MUMP-1, MUMP-2, and MUMP-3 killed Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, Mycobacterium fortuitum, and Cryptococcus neoformans in vitro. MUMP-1 resembled an H1 histone but was unusual because its N-terminal residue (serine) was not N acetylated. Although MUMP-2 was N terminally blocked, its high lysine/arginine ratio and its reactivity with an antibody to H1 histones suggested that it also belonged to the H1 histone family. MUMP-3 was identical to histone H2B in 30 of 30 amino-terminal residues. Although the antimicrobial properties of histones have been recognized for decades, this is the first evidence that such proteins may endow the lysosomal apparatus of macrophages with nonoxidative antimicrobial potential. Other MUMPs, including some with a more restricted antimicrobial spectrum and one that appeared to be induced in RAW264.7 cells after gamma interferon stimulation, were noted but remain to be characterized.
Insights
Murine microbicidal proteins (MUMPs), including histones, were purified from macrophages. These MUMPs demonstrate broad-spectrum antimicrobial activity against bacteria and fungi in vitro.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Macrophages are key immune cells involved in pathogen clearance.
- Lysosomal pathways are crucial for intracellular microbial killing.
- Histones are known for their DNA-binding role but also possess antimicrobial properties.
Purpose of the Study:
- To identify and characterize microbicidal proteins from murine macrophages.
- To investigate the antimicrobial spectrum of purified murine microbicidal proteins (MUMPs).
- To explore the potential role of histones in macrophage-mediated nonoxidative antimicrobial activity.
Main Methods:
- Purification of murine microbicidal proteins (MUMPs) from RAW264.7 and J774A.1 macrophage cell lines, as well as primary murine peritoneal macrophages.
- Activation of macrophages using gamma interferon.
- In vitro antimicrobial assays against a panel of bacteria (Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, Mycobacterium fortuitum) and fungi (Cryptococcus neoformans).
- Protein identification and characterization, including N-terminal sequencing and antibody reactivity analysis.
Main Results:
- Three MUMPs (MUMP-1, MUMP-2, MUMP-3) were purified and found to possess broad-spectrum antimicrobial activity.
- MUMP-1 showed similarity to H1 histone, with an unusual non-acetylated N-terminus.
- MUMP-2, likely an H1 histone family member, and MUMP-3, identified as histone H2B, also exhibited microbicidal properties.
- These findings suggest histones contribute to the nonoxidative antimicrobial potential of the macrophage lysosomal apparatus.
Conclusions:
- Murine macrophages produce and utilize microbicidal proteins, including histones, for antimicrobial defense.
- Histones play a significant role in the nonoxidative killing mechanisms of macrophages.
- Further characterization of other MUMPs and their specific roles in innate immunity is warranted.