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Postnatal development of resistance against infection in an experimental model
Abstract:
The postnatal development of resistance against infection was monitored by the treatment of juvenile mice with a virulent strain of Listeria monocytogenes. It could be shown that until day 10 after birth, young mice succumbed to an infection with even minimal doses of bacteria. Between day 15 and 30, the resistance against infection gradually increases until the rather constant level of grown-up animals is reached (Fig. 1). Juvenile mice that survive the primary infection are able to build up a state of immunity, which is rather similar to that of grown-up mice (Fig 3). Immunity against L. monocytogenes is mainly expressed by a functionally active T-cell system; the maturity of these cells in 15 days old mice could be demonstrated by the transfer of cells to "nude"-mice, which lack a thymus (Fig. 4). A significant increase of the non-specific resistance can be achieved even in 10 days old mice by the injection of adjuvants like pertussis organisms or endotoxin of Salmonella typhi some days before infection (Fig. 5, Fig. 6). Our findings suggest that a deficiency of functionally active macrophages is responsible for the insufficient resistance against infection with L. monocytogenes in young mice.
Insights
Young mice gain resistance to Listeria monocytogenes infection as they mature. Enhancing immune responses with adjuvants improves resistance in 10-day-old mice, suggesting macrophage function is key.
Area of Science:
- Immunology
- Microbiology
- Developmental Biology
Background:
- Postnatal development of immune resistance is crucial for survival.
- Juvenile mice exhibit increased susceptibility to bacterial infections.
Purpose of the Study:
- To investigate the development of resistance against Listeria monocytogenes infection in mice.
- To understand the immunological mechanisms underlying this developing resistance.
Main Methods:
- Infection of juvenile mice with Listeria monocytogenes.
- Monitoring survival rates and immune responses at different postnatal ages.
- Cell transfer experiments to assess T-cell function in immunodeficient mice.
- Administration of adjuvants (pertussis organisms, Salmonella typhi endotoxin) to enhance resistance.
Main Results:
- Mice up to 10 days old were highly susceptible to L. monocytogenes.
- Resistance increased significantly between days 15 and 30 post-birth.
- Survivors developed immunity comparable to adult mice.
- T-cell system maturity was evident in 15-day-old mice.
- Adjuvant treatment enhanced resistance in young mice.
Conclusions:
- Functional T-cell activity contributes to L. monocytogenes immunity.
- Macrophage deficiency likely underlies the poor resistance in young mice.
- Immune system maturation is critical for overcoming bacterial infections postnatally.