Types of asthma
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Summary
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These studies suggest asthma can be categorized into type 2-high and type 2-low endotypes, eosinophilic and noneosinophilic subtypes, and various phenotypes influenced by immune pathways, genetic and environmental factors, and airway remodeling.
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Types of Asthma: Phenotypes and Endotypes
Asthma is a complex and heterogeneous disease characterized by chronic inflammation of the airways. It is no longer viewed as a single disease but rather as a collection of related conditions with distinct clinical presentations (phenotypes) and underlying biological mechanisms (endotypes). Understanding these variations is crucial for effective management and treatment.
Type 2 (T2) High Asthma
Characteristics and Mechanisms
Type 2 (T2) high asthma is characterized by the presence of type 2 cytokines such as IL-4, IL-5, and IL-13, which lead to hallmark features like eosinophilia, mucus hypersecretion, bronchial hyperresponsiveness (BHR), and elevated IgE levels . This subtype is often associated with allergic reactions and is the most well-characterized form of asthma.
Clinical Implications
Patients with T2-high asthma often respond well to corticosteroids and other biologic agents targeting specific cytokines, such as anti-IL-5 and anti-IL-4/IL-13 therapies . These treatments have significantly improved outcomes for patients with this subtype.
Type 2 (T2) Low Asthma
Characteristics and Mechanisms
Type 2 (T2) low asthma is less understood and is characterized by the absence of the typical type 2 cytokine profile. Instead, it is often associated with neutrophilic inflammation, obesity-related systemic inflammation, and a poor response to corticosteroids . This subtype may involve different immune pathways, including those driven by Th17 cells and type 3 innate lymphoid cells (ILC3s) .
Clinical Implications
Management of T2-low asthma is more challenging due to its poor response to conventional therapies. Research is ongoing to develop targeted treatments for this subtype, focusing on different inflammatory pathways .
Allergic Eosinophilic Asthma
Characteristics and Mechanisms
Allergic eosinophilic asthma is a subtype of T2-high asthma characterized by a strong allergic component. It involves the activation of Th2 cells and type 2 innate lymphoid cells (ILC2s), leading to eosinophilic infiltration and airway inflammation . This subtype is often triggered by environmental allergens and pollutants.
Clinical Implications
Patients with allergic eosinophilic asthma benefit from allergen avoidance and targeted biologic therapies that reduce eosinophilic inflammation .
Non-Allergic Eosinophilic Asthma
Characteristics and Mechanisms
Non-allergic eosinophilic asthma also falls under the T2-high category but occurs without a clear allergic trigger. It is driven primarily by ILC2s and involves similar eosinophilic inflammation .
Clinical Implications
Treatment strategies for non-allergic eosinophilic asthma are similar to those for allergic eosinophilic asthma, focusing on reducing eosinophilic inflammation through targeted biologic therapies.
Neutrophilic Asthma
Characteristics and Mechanisms
Neutrophilic asthma is a subtype of T2-low asthma characterized by neutrophilic inflammation rather than eosinophilic. It is often associated with environmental factors such as infections, smoking, and pollution, and involves Th17 cells and IL-17 .
Clinical Implications
This subtype is particularly challenging to treat due to its poor response to corticosteroids. Research is focused on developing new therapies targeting neutrophilic inflammation .
Mixed Granulocytic and Paucigranulocytic Asthma
Characteristics and Mechanisms
Some patients exhibit mixed granulocytic asthma, with both eosinophilic and neutrophilic inflammation, or paucigranulocytic asthma, with low levels of both types of inflammatory cells. These subtypes highlight the complexity and variability of asthma.
Clinical Implications
Treatment for these subtypes requires a personalized approach, often involving a combination of therapies targeting different inflammatory pathways.
Conclusion
Asthma is a multifaceted disease with various phenotypes and endotypes, each requiring tailored treatment strategies. Understanding the underlying mechanisms and clinical characteristics of each subtype is essential for effective management and the development of new therapies. Advances in biologic treatments and personalized medicine hold promise for improving outcomes for all asthma patients.
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