Allergy, parasites, and the hygiene hypothesis

Area of Science:

• Immunology
• Epidemiology

Background:

• Allergic diseases have increased in industrialized nations, often linked to reduced childhood infections.
• The hygiene hypothesis suggests reduced microbial exposure leads to imbalanced T helper 1 (TH1) and T helper 2 (TH2) cell responses, favoring allergies.

Purpose of the Study:

• To investigate the relationship between persistent infections and allergic diseases.
• To explore the role of anti-inflammatory cytokines in modulating immune responses to infections and allergies.

Main Methods:

• Review of immunological explanations for allergy prevalence.
• Analysis of epidemiological data on infections and allergic diseases.
• Examination of cytokine profiles, including interleukin-10, in response to helminth infections.

Main Results:

• The notion that reduced infections increase allergies is challenged by rising TH1-autoimmune diseases and lack of allergy association with TH2-skewed helminth infections.
• Long-term helminth infections are associated with elevated anti-inflammatory cytokines like interleukin-10.
• These cytokines show an inverse correlation with allergy prevalence.

Conclusions:

• Persistent immune challenges, such as helminth infections, induce a strong anti-inflammatory regulatory network.
• This network provides a unifying explanation for the inverse association observed between many infections and allergic disorders.
• The findings suggest a more complex interplay between infection, immune regulation, and allergy development than previously understood.