Pathogens as commensals: microbial priming of the immune system and heterologous protection
Thomas Belcher1, Emily J Stevens1
1School of Life Sciences, Keele University, Keele, UK.
Abstract:
Exposure to microbes is essential to promote the development of the host's immune system. Commensal microbes (i.e. the microbiota) which are acquired early in life play a vital role in immune priming. Whilst many organisms within the microbiota are harmless, some can be considered opportunistic pathogens. Examples include Staphylococcus aureus, Streptococcus pneumoniae and Pseudomonas aeruginosa, and these organisms can also contribute to the development of a healthy host immune system. At the extreme end of the spectrum, pathogens which typically do not form part of the microbiota (e.g. Mycobacterium tuberculosis, Bordetella pertussis and Salmonella Typhimurium) have been shown to provide cross-protection against infectious and non-infectious diseases in mice. Attenuated strains of these pathogens, such as BPZE1, could have clinical applications, whilst Bacillus Calmette-Guérin, a live-attenuated Mycobacterium bovis strain, has been shown to have non-specific effects against cancers and other diseases. A wide range of organisms, from harmless microbiota to potentially life-threatening infections, interact with the host immune system and can prime or modulate the immune response in different ways. In this review, we discuss the important role that pathogens, including opportunistic components of the microbiota, play in the development and maintenance of host immunity to a wide range of infectious and non-infectious diseases.
Insights
Microbes, including commensals and pathogens, are crucial for developing a robust immune system. Exposure to diverse microorganisms, even opportunistic pathogens, primes and modulates host immunity against various diseases.
Area of Science:
- Immunology
- Microbiology
- Infectious Diseases
Background:
- Microbial exposure is vital for immune system development.
- Commensal microbes (microbiota) acquired early in life are key for immune priming.
- Opportunistic pathogens and non-microbiota pathogens can also influence immune responses.
Purpose of the Study:
- To review the multifaceted role of microbial exposure in host immunity.
- To explore how commensals, opportunistic pathogens, and classical pathogens impact immune development and maintenance.
- To discuss the potential clinical applications of specific microbial strains.
Main Methods:
- Literature review of studies on host-microbe interactions and immune responses.
- Analysis of research on commensal microbiota, opportunistic pathogens (e.g., Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa), and classical pathogens (e.g., Mycobacterium tuberculosis, Bordetella pertussis, Salmonella Typhimurium).
- Examination of findings on attenuated pathogen strains (e.g., BPZE1) and vaccines (e.g., Bacillus Calmette-Guérin).
Main Results:
- Commensal microbes are essential for initial immune system education.
- Opportunistic pathogens can contribute to immune system health.
- Exposure to non-microbiota pathogens and their attenuated forms can confer cross-protection against diseases.
- Live-attenuated vaccines like Bacillus Calmette-Guérin demonstrate broad, non-specific protective effects.
Conclusions:
- A wide spectrum of microorganisms, from commensals to pathogens, significantly influences host immune system development and function.
- Understanding these interactions is key to developing novel strategies for preventing and treating infectious and non-infectious diseases.
- Further research into microbial modulation of immunity holds promise for therapeutic interventions.
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