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Failure of synthetic muramyl dipeptide to increase antibacterial resistance
Abstract:
Synthetic muranyl dipeptide, which potentiates antibody production and cellular immune responses at a dosage of 100 to 500 micrograms, did not enhance resistance to intravenous infection with a sublethal dose of 2 X 10(3) to 4 X 10(3) viable Listeria monocytogenes cells in mice when intraperitoneally injected either 20 min or 5 days before infection. Similarly, blockade of the mononuclear phagocyte system by dextran sulfate 500 could not be overcome by pretreatment with muramyl dipeptide. In contrast, dextran sulfate 500-induced loss of antibacterial resistance was found to be completely abolished by intraperitoneal injection of 3 X 10(9) killed Bordetella pertussis organisms when given 4 days before injection of dextran sulfate 500, i.e., 5 days before infection. B. pertussis were also effective in enhancing antibacterial resistance when administered 5 days before infection. The different behavior of the two adjuvants tested is assumed to be due to their different nonspecific proliferative capacities. Thus, B. pertussis are assumed to act by direct stimulation of the mononuclear phagocyte system whereas muramyl dipeptide does not.
Insights
Synthetic muramyl dipeptide did not enhance Listeria monocytogenes resistance in mice. However, killed Bordetella pertussis organisms effectively restored antibacterial resistance, suggesting different adjuvant mechanisms.
Area of Science:
- Immunology
- Microbiology
Background:
- Adjuvants like synthetic muramyl dipeptide (MDP) can enhance immune responses.
- The mononuclear phagocyte system plays a crucial role in antibacterial resistance.
Purpose of the Study:
- To investigate the efficacy of MDP and Bordetella pertussis as adjuvants in enhancing antibacterial resistance against Listeria monocytogenes infection in mice.
- To explore the mechanisms by which these adjuvants modulate immune responses and resistance.
Main Methods:
- Mice were infected with Listeria monocytogenes after intraperitoneal administration of synthetic muramyl dipeptide or killed Bordetella pertussis.
- Mononuclear phagocyte system blockade was induced using dextran sulfate 500.
- Antibacterial resistance was assessed by monitoring survival and bacterial load.
Main Results:
- Synthetic muramyl dipeptide did not enhance resistance to Listeria monocytogenes infection, even when administered 20 minutes or 5 days before infection.
- Pretreatment with muramyl dipeptide did not overcome the immunosuppression caused by dextran sulfate 500.
- Killed Bordetella pertussis organisms administered 5 days before infection completely abolished the loss of antibacterial resistance induced by dextran sulfate 500.
Conclusions:
- Synthetic muramyl dipeptide and Bordetella pertussis exhibit different adjuvant properties, likely due to variations in their capacity to stimulate the mononuclear phagocyte system.
- Bordetella pertussis appears to directly stimulate the mononuclear phagocyte system, thereby enhancing antibacterial resistance, while muramyl dipeptide does not exhibit this effect.