Related Experiment Videos
Macrophages produce somnogenic and pyrogenic muramyl peptides during digestion of staphylococci
1Department of Physiology and Biophysics, University of Tennessee, Memphis 38163.
Abstract:
Muramyl peptides have a variety of biological effects in mammals, including enhancement of the immune response, sleep, and body temperature. Although mammals lack biosynthetic pathways for muramyl peptides, they are found in mammals and are well known as components of bacterial cell walls. This suggests that phagocytic mammalian cells digest bacterial cell walls and produce biologically active muramyl peptides. Staphylococcal cell walls were radioactively labeled during growth of the bacteria. During the digestion of these radiolabeled bacteria, murine bone marrow macrophages produced low-molecular-weight substances that coeluted chromatographically with the radioactive cell wall marker. Further separation of these substances using reversed-phase high-performance liquid chromatography resulted in the isolation of substances with high specific biological activity. Intracerebroventricular injection of rabbits with these substances induced an increase in slow-wave sleep and body temperature and a suppression of rapid-eye-movement sleep. The characteristics of the biological responses and the chromatographic behavior of the active components are consistent with those of muramyl peptides. The ability of macrophages to tailor muramyl peptides from peptidoglycan may provide an amplification step for the immune response. Muramyl peptides released by macrophages may also act as mediators for various facets of the acute phase response elicited by bacterial infections such as fever and sleep.
Insights
Macrophages digest bacterial cell walls to produce biologically active muramyl peptides. These peptides influence immune response, sleep, and body temperature in mammals, acting as mediators in acute phase responses.
Area of Science:
- Immunology
- Microbiology
- Neuroscience
Background:
- Muramyl peptides, bacterial cell wall components, exert significant biological effects in mammals, including immune modulation, sleep regulation, and thermoregulation.
- Mammals lack endogenous muramyl peptide synthesis, implying exogenous sources, likely from bacterial digestion.
Purpose of the Study:
- To investigate the production of biologically active muramyl peptides by mammalian cells.
- To characterize the effects of these derived peptides on mammalian physiological processes.
Main Methods:
- Radioactive labeling of Staphylococcal cell walls during bacterial growth.
- Digestion of labeled bacteria by murine bone marrow macrophages.
- Chromatographic separation (including reversed-phase HPLC) of low-molecular-weight substances.
- Intracerebroventricular injection of isolated substances into rabbits to assess biological effects.
Main Results:
- Macrophages produced low-molecular-weight substances that coeluted with bacterial cell wall markers during digestion.
- Purified substances exhibited high specific biological activity.
- Injection induced increased slow-wave sleep and body temperature, with suppressed rapid-eye-movement sleep in rabbits.
- Activity and chromatographic properties were consistent with muramyl peptides.
Conclusions:
- Mammalian macrophages can process bacterial peptidoglycans to yield biologically active muramyl peptides.
- These peptides may serve as immune response amplifiers and mediators of acute phase responses like fever and sleep changes during bacterial infections.