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Enhanced resistance to Listeria monocytogenes due to non-specifically activated macrophages in aged mice
Abstract:
Age-related modification of protection to L. monocytogenes by macrophages was examined. Cumulative mortality rates of old (15-month-old) or very old (24 to 26-month-old) mice were lower than that of young (3-month-old) mice after an intravenous inoculation of L. monocytogenes. The numbers of bacteria in the livers and spleens of old or very old mice were smaller than that of young mice at an early stage of infection (1 day or 3 days). Adversely, the numbers of bacteria in old or very old mice were larger than in young mice at a late stage (7 days). Enhanced resistance to L. monocytogenes was shown not only in the case of systemic infection after an intravenous bacterial challenge, but also in the case of local infection in the thigh muscle or subcutaneous air cavity. The number of macrophages accumulating to the infected sites in old mice was not larger over a five day period than that in young mice in the case of local infection in a subcutaneous air cavity. Peritoneal macrophages derived from old mice suppressed more effectively the bacterial growth within macrophages in vitro than did those derived from young mice. These results suggest that the macrophage function of aged mice is not impaired and non-specifically activated macrophages contribute to the protection to L. monocytogenes in aged mice.
Insights
Older mice show enhanced protection against Listeria monocytogenes infection. Macrophage function in aged mice is not impaired, suggesting activated macrophages contribute to this increased resistance.
Area of Science:
- Immunology
- Gerontology
- Microbiology
Background:
- Aging can alter immune responses, potentially increasing susceptibility to infections.
- The role of macrophages in age-related changes in host defense against Listeria monocytogenes is not fully understood.
Purpose of the Study:
- To investigate age-related modifications in macrophage-mediated protection against Listeria monocytogenes.
- To determine if aged mice exhibit altered resistance and immune cell function during infection.
Main Methods:
- Comparative analysis of mortality rates and bacterial loads in young and aged mice following intravenous Listeria monocytogenes challenge.
- Assessment of bacterial growth in local infection models (thigh muscle, subcutaneous air cavity).
- In vitro evaluation of peritoneal macrophage phagocytic and bacterial suppression capabilities.
Main Results:
- Aged mice exhibited lower cumulative mortality rates and reduced bacterial burdens in early infection stages compared to young mice.
- Enhanced resistance was observed in both systemic and local infection models.
- Peritoneal macrophages from aged mice demonstrated superior suppression of intracellular bacterial growth in vitro.
- Macrophage accumulation at infection sites was not significantly different between young and aged mice.
Conclusions:
- Macrophage function in aged mice is not impaired and contributes to enhanced protection against Listeria monocytogenes.
- Non-specifically activated macrophages in aged individuals play a crucial role in combating Listeria monocytogenes infections.