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Updated: Aug 15, 2026
Measuring Bacterial Load and Immune Responses in Mice Infected with Listeria monocytogenes
Published on: August 9, 2011
Stimulation of monocyte production by an endogenous mediator induced by a component from Listeria monocytogenes
Abstract:
A monocytosis-producing activity (MPA) is present in a saline-extractable material (SE) from Listeria monocytogenes. The mechanism of stimulation of monocyte production by SE was studied. Serum obtained from mice at appropriate times after injection of SE induced monocytosis in normal recipients. The monocytosis-inducing activity present in serum differed from SE with respect to timing of the monocytosis, fractionation pattern on a Sephadex G-200 column, and thermolability. The minimum dose of SE capable of producing a monocytosis was 100 micrograms. Antibody to SE capable of detecting SE at a concentration of greater than 5 micrograms/ml failed to detect SE in samples of active serum. Therefore it seemed highly unlikely that activity in serum was due to the presence of trace amounts of SE. The activity present in serum was thermolabile and had a molecular weight of about 38,000. The data are consistent with the hypothesis that injection of SE caused the production or release of an endogenous mediator capable of stimulating monocytosis.
Insights
Listeria monocytogenes contains a monocyte-producing activity (MPA). This activity in mice serum, distinct from the original material, suggests an endogenous mediator stimulates monocyte production.
Area of Science:
- Immunology
- Microbiology
Background:
- Listeria monocytogenes possesses a monocytosis-producing activity (MPA).
- The saline-extractable material (SE) from L. monocytogenes is the source of this MPA.
Purpose of the Study:
- To elucidate the mechanism by which SE stimulates monocyte production.
- To characterize the monocytosis-inducing activity found in mouse serum after SE injection.
Main Methods:
- Injection of SE into mice and collection of serum.
- Analysis of serum activity using Sephadex G-200 fractionation and thermolability tests.
- Determination of minimum effective dose and antibody assays.
Main Results:
- Serum from SE-injected mice induced monocytosis in normal recipients.
- The serum activity differed from SE in timing, molecular weight (approx. 38,000), and thermolability.
- Antibody assays ruled out SE contamination as the cause of serum activity.
- Minimum effective SE dose was 100 micrograms.
Conclusions:
- The findings support a hypothesis that SE induces the production or release of an endogenous mediator.
- This mediator is responsible for stimulating monocyte production (monocytosis).
- The mediator is distinct from the original SE material.
