Alergia / Hipersensibilidade Tipo I

Summary

This video delves into the role of mast cells in allergic reactions, focusing on hypersensitivity and the immune response. It explores both the immediate and late-phase reactions, explaining how mast cells release mediators like histamine and cytokines in response to allergens. The video also highlights common allergic diseases such as rhinitis, asthma, and anaphylaxis, detailing their clinical manifestations and treatments. Additionally, it addresses the protective role of mast cells in fighting infections, particularly helminth infestations, while emphasizing the complexity of allergic processes and their impact on the body.

Takeaways

• 😀 Mast cells play a crucial role in Type 1 hypersensitivity reactions, triggering both immediate and late phase responses.
• 😀 The immediate phase of an allergic reaction occurs within minutes of exposure and is characterized by swelling (papules) and redness (erythematous halo).
• 😀 In the late phase of an allergic reaction, which can last from 2 to 24 hours, inflammation occurs due to leukocyte recruitment and cytokine release.
• 😀 Histamine and other preformed mediators released by mast cells are key drivers of the immediate allergic response, causing vasodilation and plasma extravasation.
• 😀 Late phase reactions are associated with the recruitment of TH2 cells and the release of additional cytokines like IL-4, IL-5, and IL-13.
• 😀 Allergic diseases such as rhinitis, asthma, and atopic dermatitis are linked to mast cell degranulation and the subsequent inflammatory response.
• 😀 In asthma, the main pathological features include reversible airway obstruction, chronic bronchial inflammation, and excessive mucus production.
• 😀 Anaphylaxis is a severe systemic allergic reaction that can be triggered by food, insect stings, or certain medications, leading to shock, airway obstruction, and cardiovascular collapse.
• 😀 Immediate treatment for anaphylaxis involves the injection of epinephrine to reverse the effects of vasodilation and airway constriction.
• 😀 Mast cells also have a protective role in fighting infections, such as helminths, through antibody-dependent cellular cytotoxicity (ADCC) and the activation of eosinophils.
• 😀 Allergic reactions can vary depending on the antigen exposure, the affected tissue, and the age of the inflammatory process, which influences the severity of the response.

Q & A

What is the immediate phase of a Type 1 hypersensitivity reaction?

The immediate phase occurs within minutes of allergen exposure, where preformed mediators like histamine are released from sensitized mast cells. This leads to vascular responses, swelling (papules), and erythematous halos around the affected area, causing immediate allergic symptoms.

What is the role of histamine in the immediate phase of an allergic reaction?

Histamine acts on endothelial cells, causing vasodilation and increased vascular permeability. This results in the leakage of plasma and proteins, leading to swelling (papules) and erythema (redness) around the affected area.

What are the key mediators involved in the late phase of an allergic reaction?

In the late phase, mediators like TNF and IL-1 produced by mast cells regulate the expression of adhesion molecules. These molecules enable leukocytes to adhere to the blood vessel walls and migrate to the site of inflammation, causing ongoing inflammatory reactions.

How do leukocytes contribute to the late phase of hypersensitivity?

Leukocytes, once recruited to the site of inflammation, degranulate and release cytokines and other factors that amplify the inflammatory response. This causes the persistence of the allergic reaction beyond the immediate phase.

What is the significance of Th2 cells in allergic reactions?

Th2 cells play a dominant role in allergic reactions by releasing cytokines like IL-4, IL-5, and IL-13. These cytokines promote the activation of mast cells, eosinophils, and other immune cells, contributing to the chronic nature of allergic inflammation.

How is asthma related to allergic reactions?

Asthma is an inflammatory disease often triggered by allergic reactions. In 70% of asthma cases, IgE-mediated hypersensitivity occurs, leading to airway inflammation, bronchospasm, mucus production, and difficulty breathing. Th2 cells are the predominant lymphocytes in allergic asthma.

What is anaphylaxis, and how does it differ from other allergic reactions?

Anaphylaxis is a severe, systemic allergic reaction characterized by airway obstruction, cardiovascular collapse, and potentially death. It is an immediate hypersensitivity response that affects the whole body, unlike localized reactions seen in conditions like rhinitis or asthma.

What are the typical triggers for anaphylaxis?

Common triggers of anaphylaxis include food allergens, insect venom (e.g., bee stings), certain medications (e.g., penicillin), and other allergens that can rapidly activate mast cells throughout the body, leading to a life-threatening response.

What is the role of epinephrine in treating anaphylaxis?

Epinephrine is used as the first-line treatment for anaphylaxis. It reverses the effects of vasodilation, reduces the release of inflammatory mediators, and restores vascular tone to prevent shock and airway obstruction.

Can mast cells have a protective role beyond causing allergic reactions?

Yes, mast cells play a protective role, especially in defense against infections like helminths (intestinal worms). They release mediators that help expel parasites and contribute to innate immune responses during bacterial infections, apart from their role in allergic reactions.