Allergy

Definition

An allergy is an abnormal immune response to a substance (allergen) that is usually harmless, causing symptoms ranging from mild to severe. This hypersensitivity occurs when the immune system mistakenly identifies a benign substance as a threat, leading to the activation of specific T cell subsets and other immune components.

5 Must Know Facts For Your Next Test

1. Allergic reactions can be classified into four types: IgE-mediated (Type I), cytotoxic (Type II), immune complex-mediated (Type III), and delayed-type hypersensitivity (Type IV).
2. T helper 2 (Th2) cells are particularly significant in allergies, as they promote the production of IgE and the activation of mast cells in response to allergens.
3. Common allergens include pollen, pet dander, certain foods, and insect stings, which can trigger various symptoms like sneezing, itching, and anaphylaxis.
4. The hygiene hypothesis suggests that a lack of early childhood exposure to infectious agents and microbes may contribute to the rise in allergic diseases.
5. Treatment options for allergies may include avoidance of allergens, antihistamines, corticosteroids, and immunotherapy to desensitize the immune response.

Review Questions

• How do T helper 2 (Th2) cells contribute to the development of an allergic response?
  • T helper 2 (Th2) cells play a crucial role in allergic responses by producing cytokines such as IL-4 and IL-13. These cytokines promote B cell activation, leading to the production of IgE antibodies specific to the allergen. The binding of IgE to mast cells sensitizes them, causing them to release histamine and other inflammatory mediators upon subsequent exposure to the allergen, resulting in allergy symptoms.
• Discuss the different types of allergic reactions and their underlying mechanisms involving T cell subsets.
  • Allergic reactions can be categorized into four types based on their underlying mechanisms. Type I reactions are mediated by IgE antibodies and Th2 cells, leading to rapid responses like anaphylaxis. Type II involves IgG or IgM antibodies causing cell damage through cytotoxicity. Type III reactions involve immune complexes that trigger inflammation. Lastly, Type IV reactions are delayed-type hypersensitivity mediated by CD4+ T helper 1 (Th1) or CD8+ cytotoxic T cells. Understanding these mechanisms helps tailor treatment approaches for allergies.
• Evaluate the potential impact of T cell subset imbalances on the prevalence and severity of allergic diseases in modern society.
  • The increasing prevalence of allergic diseases may be linked to imbalances in T cell subsets, particularly an overactive Th2 response relative to Th1 responses. In modern society, factors like decreased exposure to infectious agents during childhood could shift this balance towards Th2 dominance, resulting in heightened IgE production and allergic sensitivities. This shift could explain the rise in conditions like asthma and hay fever. Evaluating these imbalances provides insight into developing preventive strategies and therapies aimed at restoring immune balance.

Related terms

IgE:

Immunoglobulin E (IgE) is a class of antibody that plays a key role in allergic reactions by binding to allergens and triggering histamine release from mast cells.

Mast Cells:

Mast cells are immune cells that release histamine and other mediators during an allergic reaction, contributing to inflammation and allergy symptoms.

T helper cells: A subset of T cells that help regulate immune responses; specifically, Th2 cells are often involved in promoting the allergic response by producing cytokines that stimulate B cells to produce IgE.