Hosts, microbiomes, and the evolution of critical windows

Area of Science:

• Evolutionary ecology
• Immunology
• Microbial ecology

Background:

• Absence of early microbial exposure leads to immune overreaction (e.g., allergies, autoimmunity).
• A critical window exists for immune system tolerance learning, after which learning is impaired.
• Evolutionary selection has shaped diverse mechanisms for these critical windows.

Purpose of the Study:

• To explore the evolutionary ecology of critical windows for immune tolerance.
• To model how environmental and microbial factors influence the optimal length of critical windows.
• To predict the impact of declining microbial diversity on immune health.

Main Methods:

• Developed evolutionary models incorporating demographic and epidemiological transitions.
• Analyzed direct and indirect effects of microbes on host mortality and fitness.
• Investigated microbial transmission dynamics (magnitude, duration, reinfection, vertical, seasonality).

Main Results:

• Indirect microbial effects significantly alter the optimal critical window length.
• Factors like transmission dynamics and host demography redistribute microbial encounters across age.
• Declining microbial abundance and diversity are predicted to increase immune dysfunction.

Conclusions:

• Evolutionary ecology and host-microbe interactions shape critical windows for immune tolerance.
• Current loss of microbial diversity may create mismatches with evolved immune systems.
• This can lead to increased immune dysfunction and disease later in life.