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Altered cell-averaged microviscosity of murine peritoneal macrophages undergoing activation in vivo or in vitro
Abstract:
The cell-averaged microviscosity of intact murine peritoneal mononuclear phagocytes in various stages of activation was assessed by quantifying fluorescent depolarization of 1,6-diphenyl-1,3,5-hexatriene. Macrophages activated in vivo with Mycobacterium bovis, strain BCG, were significantly more fluid than resident peritoneal macrophages, responsive macrophages elicited with thioglycollate broth, proteose peptone broth, or fetal bovine serum, or primed macrophages elicited with pyran copolymer, MVE-2. Specifically, the cell-averaged microviscosity decreased from a mean of 3.47 +/- .07 eta 25 degrees C (poise) (range of 3.32 to 3.67 p) to 2.62 eta 25 degrees C. Exposure of responsive macrophages in vitro to bacterial endotoxin plus hybridoma supernatants containing macrophage-activating factor or purified recombinant interferon gamma resulted in decreased microviscosity; the largest effect was seen after 24 hr. Macrophages primed in vivo with MVE-2 and treated in vitro with endotoxin also developed decreased microviscosity. Similar changes in microviscosity were observed in a plasma membrane-enriched fraction isolated from macrophages activated in vitro with interferon gamma and endotoxin, thus suggesting that the cell-averaged measurements reflected changes in membrane viscosity. The optimum concentration of MAF-inducing decreased overall microviscosity was identical to that for inducing tumoricidal capacity. Taken together, the data indicate activation of lytic capacity in murine macrophages is closely associated with decreased cell-averaged microviscosity and that this change reflects, at least in part, decreased microviscosity of the plasma membrane of these cells.
Insights
Activated macrophages exhibit reduced cell microviscosity, indicating increased membrane fluidity. This change in viscosity is linked to enhanced lytic capacity in these immune cells.
Area of Science:
- Immunology
- Cell Biology
- Biophysics
Background:
- Murine peritoneal mononuclear phagocytes (macrophages) exist in various activation states.
- Cell membrane microviscosity is a critical factor in cellular function and immune response.
Purpose of the Study:
- To assess the cell-averaged microviscosity of murine macrophages at different activation stages.
- To investigate the relationship between macrophage activation, microviscosity changes, and lytic capacity.
Main Methods:
- Quantification of fluorescent depolarization of 1,6-diphenyl-1,3,5-hexatriene in intact macrophages.
- In vivo and in vitro activation of macrophages using various stimuli (BCG, thioglycollate, endotoxin, interferon gamma).
- Isolation of plasma membrane-enriched fractions for viscosity analysis.
Main Results:
- Macrophages activated with Mycobacterium bovis strain BCG showed significantly lower microviscosity (2.62 poise) compared to resident or elicited macrophages (3.47 poise).
- In vitro activation with endotoxin and macrophage-activating factor (MAF) or interferon gamma decreased microviscosity in responsive macrophages.
- Changes in microviscosity were also observed in plasma membrane fractions, suggesting membrane alterations.
Conclusions:
- Macrophage activation, particularly for lytic capacity, is closely associated with decreased cell-averaged microviscosity.
- The observed decrease in microviscosity reflects, in part, reduced plasma membrane viscosity.
- These findings suggest a biophysical basis for macrophage activation and function.