Asthma and Allergic Reactions Study Notes

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Questions and Answers

What primarily causes the wheal-and-flare reaction observed after a skin test for hypersensitivity?

Decreased blood vessel permeability

Release of leukotrienes

Release of histamine (correct)

Vasoconstriction of blood vessels

What characterizes the late-phase response following an immediate allergic reaction?

Reduced blood flow to the area

A cellular infiltrate at the allergic reaction site (correct)

Immediate release of IgE antibodies

Increased production of prostaglandins

Which response mechanism is involved in the wheezing associated with NSAID use in susceptible patients?

Inhibition of leukotriene synthesis

Stimulation of cyclooxygenase (COX)

Shunting of arachidonic acid towards leukotriene synthesis (correct)

Increased production of prostaglandins

How does immunotherapy help in reducing allergic responses?

It promotes the development of TH1 cells. Signup and view all the answers

Why do atopic children rarely develop allergic reactions to protein antigens such as tetanus toxoid despite frequent immunizations?

Mucosal presentation at low doses activates TH2 cells. Signup and view all the answers

What effect does IFN-γ have on B cells already switched to IgE production during immunotherapy?

It has no impact on existing IgE-producing B cells. Signup and view all the answers

What type of immune cells are favored by the injection of large doses of antigen subcutaneously?

TH1 cells Signup and view all the answers

What is primarily responsible for the sensation of chest tightness in asthma patients?

Narrowing of airways during expiration Signup and view all the answers

Why do bronchodilators fail to improve Frank's asthma condition?

They lack immediate effect on airway inflammation. Signup and view all the answers

What is the role of IL-5 in patients with allergic asthma?

It promotes the maturation of eosinophils. Signup and view all the answers

What is the primary reason for the hyperinflated appearance on chest radiographs in asthma?

High residual lung volume. Signup and view all the answers

What immune response predominates in allergic individuals leading to eosinophilia?

TH2 cell production. Signup and view all the answers

How do activated T cells contribute to the accumulation of eosinophils in allergic asthma?

By secreting CCL11 to attract eosinophils. Signup and view all the answers

What cellular change takes place within the airways in chronic allergic asthma?

Increased secretion of mucus and cellular infiltration. Signup and view all the answers

What is the effect of high residual lung volume on respiratory muscles?

Increases work and energy expenditure. Signup and view all the answers

Study Notes

Frank's Asthma and Allergic Reactions: Study Notes

Chest Tightness Basis: Inspiration creates negative airway pressure, enlarging airways. Expiration narrows them, exacerbated by inflammation and bronchoconstriction (as in asthma). Trapped air increases residual lung volume, requiring increased effort, leading to chest tightness. This high residual volume results in hyperinflation, visible on chest X-rays.
Radiographic Findings: Hyperinflated chest, peribronchial markings (inflammation around the airways) are characteristic of asthma.
Asthma Treatment Ineffectiveness: Asthma involves more than just smooth muscle constriction. Airway inflammation (cellular infiltration, mucus secretion, swelling) is a significant factor. Bronchodilators address only smooth muscle constriction; they are not effective in reversing chronic airway inflammation. Steroids target the inflammatory response.
Eosinophilia Basis: Allergic individuals favor a TH2 immune response over TH1, resulting in increased IL-4 and IL-13 production (triggering IgE). IL-5, also from TH2 cells, promotes eosinophil maturation. CCL11 (eotaxin) attracts eosinophils to the airways. This interplay explains the link between IgE and eosinophilia.
Wheal-and-Flare Reaction: Allergen skin tests induce a wheal-and-flare reaction in allergic individuals within 10-20 minutes. This reaction is due primarily to mast cell histamine release. Histamine increases blood vessel permeability (wheal), and blood vessel dilation creates redness (flare).
Late Phase Response: Redness and swelling recurring at skin test sites 24 hours later indicate a cellular infiltrate, a late-phase reaction, following the initial allergic reaction.
NSAIDs and Asthma: Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen can trigger wheezing in some patients. Inhaling an allergen or NSAID leads to a different pathway; this triggers an increase in leukotriene production.
Immunotherapy Mechanism: Immunotherapy aims to shift the immune response from TH2 (allergy-associated) to TH1 (anti-allergy) by repeated allergen exposure. This reduces IgE by promoting an IgG response and inhibiting mast cell and B-cell activation.
Allergic Reactions in Vaccinated Children: Despite repeated immunizations with protein antigens (e.g., tetanus toxoid), atopic children rarely develop allergic reactions. This is due to the difference in antigen presentation in vaccines compared to allergic exposures. Large-dose subcutaneous vaccination favors a TH1 response (and therefore IgG), while allergic exposures favor a TH2 response (and increased IgE) due to different antigen presentation methods (low dose, mucosal exposure).

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Description

Explore the complexities of asthma and allergic reactions with these study notes. Understand the physiological mechanisms behind chest tightness, the role of airway inflammation, and the limitations of common treatments. This content is essential for students studying respiratory medicine and allergy management.