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Maintenance of peritoneal macrophages in the steady state
M J Melnicoff1, P K Horan, E W Breslin
1Department of Immunology, Smith Kline and French Laboratories, King of Prussia, Pennsylvania.
Abstract:
Resident peritoneal macrophages (M phi) were labeled in situ by intraperitoneal (i.p.) injection of the green fluorescent cell tracking dye PKH-1. After immunofluorescence staining with M phi specific monoclonal antibodies (Mabs) and phycoerythrin (PE) second antibody, the resident M phi were labeled with both the green dye and red Mab label, while recruited M phi were labeled only with the red Mab tag. These populations were distinguished by two-color flow cytometry. PKH-1 labeled resident peritoneal M phi were followed for 1-49 days in mice that received no further treatment (steady state). Dye labeled M phi were still detectable after 49 days in vivo, although their green fluorescence intensity had decreased steadily over time. The decrease in dye intensity was limited to M phi, as the fluorescence intensity of PKH-1 labeled peritoneal lymphocytes did not change. Resident M phi populations were clearly separated from recruited M phi by the intensity of their staining with PKH-1 for up to 28 days. No decrease in the number of resident (dye labeled) peritoneal M phi was observed over 1-28 days. These data indicate that resident peritoneal M phi were not replaced by recruited blood monocytes in the steady state.
Insights
Resident peritoneal macrophages (M phi) persist long-term, as shown by a dye-labeling study. These key immune cells are not replaced by blood monocytes in a steady state.
Area of Science:
- Immunology
- Cell Biology
Background:
- Peritoneal macrophages (M phi) are crucial immune cells residing in the abdominal cavity.
- Understanding macrophage turnover is vital for immunology and disease research.
Purpose of the Study:
- To investigate the self-renewal and replacement of resident peritoneal macrophages in mice.
- To differentiate between resident and newly recruited macrophages.
Main Methods:
- In situ labeling of resident peritoneal macrophages using the green fluorescent dye PKH-1.
- Distinguishing resident (green and red labeled) from recruited (red labeled) macrophages via two-color flow cytometry.
- Tracking dye-labeled macrophages over 49 days in a steady-state condition.
Main Results:
- Dye-labeled resident macrophages remained detectable for up to 49 days, with decreasing fluorescence intensity.
- Resident and recruited macrophage populations were distinguishable by dye intensity for 28 days.
- No significant decrease in the number of resident macrophages was observed over 28 days.
Conclusions:
- Resident peritoneal macrophages exhibit long-term stability and are not replaced by circulating monocytes under steady-state conditions.
- The findings challenge the notion of rapid macrophage turnover in this tissue.
- This study provides critical insights into the persistence and maintenance of resident immune cell populations.