Type I hypersensitivity (IgE-mediated hypersensitivity) - causes, symptoms, pathology

Summary

The video script explains hypersensitivity, focusing on type one reactions mediated by IgE antibodies. It details how allergens trigger allergic responses through a two-step process involving sensitization and subsequent exposure. The script delves into the genetic predisposition to allergies, the role of T-helper cells and interleukins in the immune response, and the release of mediators like histamine causing symptoms. It also covers the treatment options for managing allergic reactions, including antihistamines, corticosteroids, and epinephrine, emphasizing the importance of medical attention in severe cases.

Takeaways

• 🛡️ Hypersensitivity is an immune system reaction that can damage the body instead of protecting it.
• 🔍 There are four types of hypersensitivities, with Type I being IgE-mediated and involving immediate reactions.
• 🌟 The term 'allergy' originates from Greek words meaning 'other' and 'reactivity', referring to reactions to external molecules.
• 👃 Allergic reactions can occur from various sources, including foods, animal dander, bee stings, and pollen.
• 🧬 Genetic predisposition plays a role in allergies, making them more common within families.
• 🔑 The process of an allergic reaction involves two steps: sensitization upon first exposure and a more serious reaction upon subsequent exposure.
• 🧬 T-helper cells, particularly the TH2 type, are crucial in the development of Type I hypersensitivity reactions.
• 💉 Interleukins such as IL-4, IL-5, and IL-10 influence the differentiation of T-helper cells into TH2 cells.
• 🚀 The production of IgE antibodies and the activation of eosinophils are key components of the allergic response.
• 🏥 During an allergic reaction, mast cells release mediators like histamine, causing symptoms such as bronchoconstriction and edema.
• 🚑 Severe allergic reactions can lead to anaphylactic shock, which requires immediate medical attention.
• 💊 Treatment for Type I hypersensitivity can include antihistamines, corticosteroids, and epinephrine to manage symptoms and prevent anaphylactic shock.

Q & A

What is hypersensitivity and how does it differ from a normal immune response?

Hypersensitivity is a condition where the immune system reacts to a substance in a way that ends up damaging the body instead of protecting it. Unlike a normal immune response that defends the body against harmful invaders, hypersensitivity involves an overreaction to typically harmless substances.

How many types of hypersensitivities are there and what are they classified based on?

There are four different types of hypersensitivities. They are classified based on the mechanisms of the immune system response, such as the type of antibodies involved, like Immunoglobulin E (IgE) in type one hypersensitivity.

What is the role of IgE in type one hypersensitivity reactions?

IgE antibodies play a crucial role in type one hypersensitivity reactions. They are involved in immediate hypersensitivity and are produced in response to allergens, leading to allergic reactions when the body encounters these substances again.

What is the origin of the term 'allergy' and what does it signify?

The term 'allergy' comes from the Greek words 'Allos' meaning 'other' and 'ergon' meaning 'reactivity'. It signifies a reaction to molecules from outside the body that most people do not react to, such as substances in food, animal dander, or pollen.

How does an allergic reaction occur in two steps as described in the script?

An allergic reaction occurs in two steps: first exposure or sensitization, where the immune system recognizes the allergen and prepares a response, and a subsequent exposure, where the immune system overreacts to the allergen, leading to symptoms of an allergic reaction.

Why do some people have a genetic predisposition to allergies?

Some people have a genetic predisposition to allergies because they possess certain genes that make their T-helper cells more sensitive to specific antigens. This genetic link is why allergies tend to run in families.

What are antigen-presenting cells and what is their function in an allergic reaction?

Antigen-presenting cells, such as dendritic cells and macrophages, are immune cells that capture antigens and present them to T-helper cells in the lymph nodes. They are essential in initiating an immune response, including the allergic reaction process.

What is the significance of TH2 cells in type I hypersensitivity?

TH2 cells, or type 2 T helper cells, are significant in type I hypersensitivity as they differentiate from naive T-helper cells upon exposure to an allergen. They release interleukins that stimulate B cells to produce IgE antibodies and eosinophils, contributing to the allergic response.

How do mast cells play a role in allergic reactions?

Mast cells play a critical role in allergic reactions by binding IgE antibodies on their surface. When the person is re-exposed to the allergen, the mast cells degranulate, releasing pro-inflammatory mediators like histamine, which cause the symptoms of an allergic reaction.

What are the 'early phase reactions' and 'late phase reactions' in an allergic response?

The 'early phase reactions' occur within minutes of the second exposure to an allergen and include symptoms like bronchoconstriction, blood vessel dilation, and edema due to the release of mediators from mast cells. 'Late phase reactions' happen 8-12 hours later and involve the recruitment of more immune cells to the site of allergen exposure, resulting in a prolonged inflammatory response.

What are some common treatments for type one hypersensitivity reactions?

Treatments for type one hypersensitivity reactions can include antihistamines to block histamine effects, corticosteroids to reduce inflammation, and epinephrine, which can be administered via an EpiPen or intravenous injection to constrict blood vessels and prevent anaphylactic shock.