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Mechanisms of ethanol-induced defects of alveolar macrophage function
Abstract:
Several defects in host defense mechanisms of alcoholics have been described, but their role in the development of infections, especially pneumonia, is uncertain. Ethanol, in concentrations of 400 mg/100 ml, inhibits phagocytosis of radiolabeled bacteria by rabbit alveolar macrophages from 73 to 80% of control. Intracellular survival of Staphylococcus aureus is increased to 131% of control by exposure to ethanol. To evaluate the mechanisms of these ethanol-induced defects, the effect of ethanol on microtubular function and changes in levels of cAMP were evaluated. Colchicine (10(-6) M), a disrupter of microtubules, produces 49% capped cells (migration of fluorescein isothiocyanate-labeled concanavalin A (FITC-ConA) to one end of the cell), but ethanol produces no capping, even at concentrations of 2000 mg/100 ml. This suggests that the ethanol effect is not mediated by disruption of microtubules. cAMP levels, measured by radioimmunoassay, increased two-fold over control values after 10 min incubation with ethanol. The increase is dose dependent with a rapid onset. The effect of ethanol on alveolar macrophages is probably complex, but changes in osmolarity and increases in cAMP levels, perhaps interrelated by some pertubation in the cell membrane, may explain the defect.
Insights
Ethanol impairs immune cells called alveolar macrophages, increasing infection risk in alcoholics. This study suggests increased cAMP levels, not microtubule disruption, explain these defects, impacting pneumonia development.
Area of Science:
- Immunology
- Cell Biology
- Toxicology
Background:
- Alcohol abuse is linked to increased infection susceptibility, particularly pneumonia.
- Defects in host defense mechanisms in alcoholics are known but their specific role in infection development remains unclear.
Purpose of the Study:
- To investigate the mechanisms behind ethanol-induced defects in alveolar macrophage function.
- To determine if ethanol affects microtubular function or cyclic adenosine monophosphate (cAMP) levels in these cells.
Main Methods:
- Rabbit alveolar macrophages were exposed to varying concentrations of ethanol.
- Phagocytosis of radiolabeled bacteria and intracellular survival of Staphylococcus aureus were assessed.
- Microtubular function was evaluated by measuring cell capping after exposure to colchicine and ethanol.
- Changes in intracellular cAMP levels were measured using radioimmunoassay.
Main Results:
- Ethanol significantly inhibited bacterial phagocytosis and increased intracellular bacterial survival.
- Ethanol did not induce cell capping, suggesting microtubule disruption is not the primary mechanism.
- Ethanol caused a dose-dependent, rapid, two-fold increase in cAMP levels in alveolar macrophages.
Conclusions:
- Ethanol impairs alveolar macrophage function, potentially contributing to increased infection risk in alcoholics.
- Elevated cAMP levels, possibly due to membrane perturbation and altered osmolarity, likely explain ethanol's detrimental effects on these immune cells.