Why do we have allergies?
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Understanding the Origins and Increase of Allergies
Introduction to Allergies: Immune System and Environmental Factors
Allergies are immune system reactions to typically harmless substances, known as allergens. These reactions are primarily mediated by Immunoglobulin E (IgE) and T helper (Th) cells, which trigger inflammation and other symptoms in various organs such as the skin, gastrointestinal tract, and respiratory system1 4. The prevalence of allergic diseases, including asthma, atopic dermatitis, and food allergies, has significantly increased over the past few decades, particularly in developed countries3 6.
Genetic and Environmental Influences on Allergies
Genetic Predisposition and Immune Response
Genetic factors play a crucial role in the development of allergies. Individuals with a hereditary predisposition to produce IgE antibodies against common environmental allergens are more likely to develop allergic diseases9. This genetic susceptibility is often coupled with a Th2-dominated immune response, which is pivotal in the pathogenesis of allergic reactions4.
Environmental Changes and Lifestyle Factors
The dramatic rise in allergy prevalence is largely attributed to environmental changes and lifestyle factors. Increased exposure to sensitizing allergens, reduced immune system stimulation during critical developmental periods, and changes in diet and microbiome composition are significant contributors2 5 6. Urbanization, climate change, and loss of biodiversity have also been identified as key factors affecting the sources and concentrations of aeroallergens and pollutants, further exacerbating allergic conditions5.
The Role of the Microbiome and Epithelial Barrier
Microbiome Alterations
Disturbances in the gut and organ-specific microbiomes are critical in the development of allergies. The composition and function of the commensal microbiota, particularly early in life, influence immune tolerance and the body's response to allergens1 10. Modern lifestyle changes, such as increased hygiene and antibiotic use, have altered the microbiome, potentially leading to a higher incidence of allergic diseases10.
Epithelial Barrier Dysfunction
Damage to epithelial surfaces in the lungs, gut, and skin is a fundamental factor in the onset of allergic diseases. The epithelium acts as a sensor of environmental stimuli, and its dysfunction can lead to a type-2 immune response, driving atopic conditions1. Factors such as air pollution, food allergens, and chemicals in modern detergents contribute to epithelial barrier damage, promoting allergic reactions1.
Mechanisms and Pathophysiology of Allergic Reactions
Allergen-Specific Immune Responses
Allergic reactions are initiated by allergen-specific Th cells, which activate a complex immune response involving the release of potent mediators and recruitment of inflammatory cells. This process leads to the clinical symptoms of allergic diseases, such as inflammation and tissue damage4. Understanding these mechanisms has opened new avenues for therapeutic interventions aimed at controlling symptoms and suppressing inflammation4.
The Exposome Concept
The concept of the exposome, which encompasses the totality of environmental exposures from preconception onward, is crucial in understanding the development and exacerbation of allergic diseases. Indoor and outdoor aeroallergens, air pollutants, and other environmental factors play a significant role in the inflammatory response to allergens5. This holistic approach highlights the need for comprehensive strategies to mitigate environmental impacts on allergy development5.
Conclusion
The increasing prevalence of allergies is a complex interplay of genetic predisposition, environmental changes, and lifestyle factors. Understanding the mechanisms underlying allergic reactions, the role of the microbiome, and the impact of environmental exposures is essential for developing effective prevention and treatment strategies. As research continues to unravel the intricacies of allergic diseases, a systems approach that considers both genetic and environmental factors will be crucial in addressing this growing public health concern.
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Most relevant research papers on this topic
The Origins of Allergy from a Systems Approach.
Allergy is a complex systemic disease influenced by epithelial dysfunction, immune tolerance, gut microbiome disturbances, diet, and age, which can be better understood and treated through targeted interventions.
Systematic ReviewThe role of environmental factors in allergy: A critical reappraisal
Environmental factors play a significant role in the development of allergic diseases, with changes in environment and lifestyle contributing to the global increase in allergy prevalence.
Why are allergies increasing?
Allergy incidence is increasing in certain 'Western' countries due to factors such as increased awareness, improved diagnostics, genetic susceptibility, psycho-social influences, allergen exposure, decreased immune-system stimulation, underlying disease, anti-allergic therapy, and pollution.
Highly CitedMechanisms of allergy and asthma.
Allergies and asthma are caused by inappropriate immune reactions to environmental proteins, with allergen-specific T helper cells playing a crucial role in the pathogenesis.
Rigorous JournalHighly CitedExternal exposome and allergic respiratory and skin diseases
The external exposome, including indoor and outdoor aeroallergens and air pollutants, plays a key role in the development and exacerbations of allergic respiratory and skin diseases.
Rigorous JournalHighly CitedThe epidemic of allergy and asthma
Understanding the cellular and molecular mechanisms of allergic diseases can lead to new public health and therapeutic interventions.
Highly CitedAllergens, sources, particles, and molecules: Why do we make IgE responses?
Allergens are foreign proteins or glycoproteins that trigger IgE antibody responses in humans, with the relationship between exposure and allergic symptoms often being obvious or delayed.
Why did evolution give us allergies?
Allergies may be linked to our interactions with insects, worms, and snakes, potentially explaining their increasing prevalence and impact on our health.
Overview of 'allergy and allergic diseases: with a view to the future'.
This issue reviews the cellular and molecular basis of atopic allergy, its associated diseases, and various treatment approaches.
Highly CitedThe Microbiome, Timing, and Barrier Function in the Context of Allergic Disease.
Lifestyle changes in Western societies may be linked to the increased prevalence of food allergies, with early life microbiome composition and function being key factors.
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