B2 W2 - Hypersensitivity and Anaphylaxis

Question 1

What are the three ways in which immune responses can harm the body?

Answer 1

Sepsis, hypersensitivity, and autoimmune diseases.

Question 2

What is hypersensitivity?

Answer 2

It is an inappropriate and excessive immunological reaction to an external antigen due to dysfunctional control of the immune system.

Question 3

What is the key difference between an allergy and anaphylaxis?

Answer 3

An allergy is a localised, often mild to moderate, reaction. Anaphylaxis, however, is a systemic and life-threatening condition.

Question 4

What is the difference between a true drug allergy and drug intolerance?

Answer 4

A true drug allergy involves a hypersensitivity reaction with characteristic immunological features, whereas drug intolerance causes unpleasant side effects like diarrhoea or nausea, without the immune system being involved.

Question 5

What is the approximate percentage of children in the UK who develop allergies during childhood?

Answer 5

It is estimated that around 7% of children in the UK develop allergies during childhood.

Question 6

How do allergy rates in developed countries compare to those in developing countries, and what are some possible explanations for this difference?

Answer 6

Allergy rates are significantly higher in developed countries. This disparity might be due to factors like improved hygiene, particularly less exposure to parasitic infections, vitamin D deficiency, and delayed introduction of food items to infants.

Question 7

What is an allergen?

Answer 7

It is an antigen that triggers a hypersensitivity reaction. The terms “allergen” and “antigen” can often be used interchangeably in this context.

Question 8

What is autoimmunity?

Answer 8

It is an inappropriate and excessive immunological reaction to a self-antigen or an auto-antigen.

Question 9

What are the key immune cells involved in allergic reactions and anaphylaxis?

Answer 9

The key cells are eosinophils, basophils, and mast cells, with mast cells playing the most prominent role.

Question 10

Briefly describe the functional classification of the immune system and its components.

Answer 10

The immune system is functionally classified into innate and adaptive systems. The innate system provides a rapid, non-specific response, while the adaptive system is slower but highly specific and generates memory.

Question 11

What are the four classic types of hypersensitivity reactions, and which two are primarily relevant to allergies and anaphylaxis?

Answer 11

The four types are Type I (immediate, IgE-mediated), Type II (cytotoxic), Type III (immune complex-mediated), and Type IV (delayed, cell-mediated). Type I and Type IV are most relevant to allergies and anaphylaxis.

Question 12

Characterise the key features of Type I hypersensitivity reactions.

Answer 12

Type I reactions are immediate, IgE-mediated responses involving mast cell degranulation and the release of vasoactive amines, lipid mediators, and cytokines.

Question 13

Provide an example of a condition that resembles an allergic reaction but may not always involve an identifiable allergen.

Answer 13

Asthma can exhibit symptoms and molecular mechanisms similar to an allergic reaction, even in the absence of an identifiable allergen.

Question 14

What are the key characteristics of Type IV hypersensitivity reactions?

Answer 14

Type IV reactions are delayed, cell-mediated responses primarily involving T lymphocytes and macrophages, resulting in a slower, more localised, and specific reaction.

Question 15

What is a prime example of a Type IV hypersensitivity reaction?

Answer 15

Allergic contact dermatitis is the most common and illustrative example of a Type IV reaction.

Question 16

Besides allergic contact dermatitis, what are other examples of Type IV hypersensitivity reactions, though not considered classic examples of inappropriate or excessive reactions?

Answer 16

Transplant rejection, the reaction in tuberculin skin tests (Mantoux and Heaf), and even the autoimmune response in multiple sclerosis involve Type IV mechanisms, though not typically classified as inappropriate or excessive reactions.

Question 17

Approximately what percentage of the population in developed countries experience an allergic reaction at some point in their lives?

Answer 17

About 20% of the population in developed countries is said to have an allergic reaction at some point.

Question 18

What is atopy, and what conditions are commonly associated with it?

Answer 18

Atopy is a predisposition to allergies, often with a familial or genetic link, commonly associated with conditions like eczema, asthma, and other allergic manifestations.

Question 19

List some common allergens and the diseases they typically cause.

Answer 19

Common allergens include pollen (causing hay fever and allergic rhinitis), house dust mites (allergic rhinitis), animal dander (allergic rhinitis), insect venoms (severe reactions like anaphylaxis), food, and drugs (potential for anaphylaxis).

Question 20

What is the first step in the development of a Type I hypersensitivity reaction?

Answer 20

The first step is exposure to the allergen, which often consists of repeated molecules, a characteristic feature that makes them prone to causing inappropriate immune responses.

Question 21

Describe the process of sensitization in a Type I hypersensitivity reaction.

Answer 21

During sensitization, the allergen is recognised by a B cell and stimulates a T helper 2 cell response. This leads to the B cell differentiating into a plasma cell that produces IgE antibodies specific to the allergen. These IgE antibodies then bind to mast cells, eosinophils, and basophils.

Question 22

Does the first exposure to an allergen usually cause symptoms?

Answer 22

No, the first exposure, or sensitization, typically doesn’t produce noticeable symptoms. It primarily primes the immune system for a subsequent reaction upon re-exposure to the same allergen.

Question 23

What happens upon a second exposure to the same allergen in a Type I hypersensitivity reaction?

Answer 23

Upon re-exposure, the allergen binds to the IgE antibodies already attached to mast cells. This cross-linking triggers mast cell activation and degranulation, releasing preformed mediators like histamine, leukotrienes, and prostaglandins, which cause the immediate allergic reaction.

Question 24

What is mast cell degranulation, and what are its consequences in a Type I hypersensitivity reaction?

Answer 24

Mast cell degranulation is the rapid release of preformed granules containing vasoactive amines, lipid mediators, and cytokines. These mediators lead to immediate effects such as vasodilation, smooth muscle contraction (e.g., in the airways), and the recruitment of additional inflammatory and immune cells, amplifying the allergic response.

Question 25

What are the three main effects of IgE receptor triggering on mast cells?

Answer 25

IgE receptor triggering causes 1) degranulation of preformed granules (histamine, proteases), 2) synthesis and release of lipid mediators (prostaglandins and leukotrienes), and 3) production and release of cytokines, all contributing to the allergic response.

Question 26

What is the underlying pathology of a Type IV hypersensitivity reaction?

Answer 26

Type IV reactions involve a T cytotoxic cell response, which is a slower, more specific process compared to the immediate response seen in Type I hypersensitivity.

Question 27

How does the timeframe and specificity of a Type IV reaction differ from a Type I reaction?

Answer 27

Type IV reactions are delayed, taking hours or days to develop, and are more localised to the specific tissue exposed to the allergen, whereas Type I reactions are immediate and can be systemic.

Question 28

While not leading to systemic anaphylaxis, are Type IV reactions still considered hypersensitivity?

Answer 28

Yes, although they don’t cause widespread anaphylaxis, Type IV reactions are still classified as hypersensitivity because they involve an inappropriate and excessive immune response to an allergen.

Question 29

Name some common allergens that can trigger Type IV hypersensitivity reactions.

Answer 29

Common allergens include nickel, metals, certain forms of latex, and chemicals like formalin.

Question 30

What is the most frequent clinical manifestation of a Type IV hypersensitivity reaction?

Answer 30

The most common example is allergic contact dermatitis, presenting with localised itching, inflammation, and dry skin in the area exposed to the allergen.

Question 31

What are some other examples of Type IV reactions, although not considered classic examples of inappropriate or excessive reactions?

Answer 31

Transplant rejection, the reaction in tuberculin skin tests (Mantoux and Heaf tests), and the autoimmune response in multiple sclerosis all involve Type IV mechanisms.

Question 32

Describe the typical clinical presentation of allergic contact dermatitis.

Answer 32

Allergic contact dermatitis develops slowly, initially presenting with itching, followed by inflammation, dry skin, and a localised rash at the site of allergen contact.

Question 33

In what situations might investigations for allergies be necessary?

Answer 33

While many allergies are diagnosed clinically, investigations can be helpful when there’s uncertainty about the diagnosis, particularly with drug allergies.

Question 34

What is the most useful test for confirming a hypersensitivity reaction, and why?

Answer 34

Tryptase, a vasoactive amine released from mast cells, eosinophils, and basophils, is the most helpful test. Elevated tryptase levels strongly suggest an allergic reaction is occurring.

Question 35

Besides tryptase, what other blood tests may be helpful in investigating hypersensitivity?

Answer 35

IgE levels and eosinophil count are often elevated in allergic reactions, although they don’t pinpoint the specific allergen.

Question 36

Describe how skin prick testing is used to identify allergens.

Answer 36

Solutions of common allergens, along with positive (histamine) and negative (saline) controls, are pricked into the skin. A positive reaction, indicated by a wheal larger than the negative control, identifies the allergen.

Question 37

When is skin patch testing preferred over skin prick testing?

Answer 37

Skin patch testing, which involves applying patches containing numerous allergens to the skin for a longer duration, is used when testing for a broader range of allergens, beyond the most common ones used in prick testing.

Question 38

What is the most effective way to manage hypersensitivity reactions?

Answer 38

Avoiding the allergen, if possible, is the most straightforward and effective way to prevent reactions.

Question 39

How do mast cell stabilisers work in managing hypersensitivity?

Answer 39

Mast cell stabilisers prevent mast cells from releasing their inflammatory mediators (degranulation), effectively blocking the allergic cascade. They are primarily used topically.

Question 40

What is the mechanism of action of antihistamines?

Answer 40

Antihistamines block histamine receptors, preventing histamine from binding and exerting its effects, such as vasodilation and smooth muscle contraction. They can be administered topically or systemically.

Question 41

Why are steroids helpful in managing severe allergic reactions or anaphylaxis?

Answer 41

Steroids exert broad anti-inflammatory and immunosuppressive effects, reducing the overall allergic response, although their effects are not immediate.

Question 42

What is the role of leukotriene receptor antagonists in allergy management?

Answer 42

They block the action of leukotrienes, which are inflammatory mediators involved in allergic reactions, offering additional symptom relief. They are usually taken orally.

Question 43

Explain the concept of allergen immunotherapy (desensitisation).

Answer 43

Allergen immunotherapy involves gradually exposing an individual to increasing doses of their allergen over an extended period. This aims to retrain the immune system to tolerate the allergen and not mount an allergic response.

Question 44

What are the risks associated with allergen immunotherapy?

Answer 44

It carries a risk of allergic reactions, including anaphylaxis, during the exposure process. Therefore, it’s typically reserved for severe allergies unresponsive to other treatments and requires careful monitoring by a healthcare professional.

Question 45

What are the key steps in managing anaphylaxis?

Answer 45

Immediate actions include:Laying the patient downAdministering high-flow oxygenProviding intravenous fluidsAdministering intramuscular adrenaline (epinephrine) as the primary treatment

Question 46

What additional medications might be used in anaphylaxis, and why?

Answer 46

Intravenous antihistamines (like chlorphenamine) can further block histamine effects. Steroids, while not providing immediate relief, can help reduce later-stage inflammation. Bronchodilators (like salbutamol) can relieve airway constriction similar to an asthma attack.

Question 47

What is an EpiPen, and how is it used?

Answer 47

An EpiPen is a self-injectable device containing a pre-measured dose of adrenaline for emergency treatment of anaphylaxis. It’s administered intramuscularly into the thigh and is designed for self-administration by patients at risk of severe allergic reactions.

Question 48

What characterises anaphylaxis as a severe type I hypersensitivity reaction?

Answer 48

Anaphylaxis is a systemic, potentially life-threatening allergic reaction involving a rapid cascade of immune responses following exposure to an allergen.

Question 49

Which allergens are more likely to trigger anaphylaxis compared to milder allergic reactions?

Answer 49

Allergens that enter the bloodstream directly, like insect venoms and medications, are more likely to cause anaphylaxis than allergens that primarily interact with mucous membranes. Food allergens are also high risk, as ingestion leads to systemic exposure.

Question 50

What are the initial symptoms of anaphylaxis?

Answer 50

Initial symptoms often include localized swelling at the exposure site (e.g., insect sting), flushed skin due to vasodilation, and a feeling of faintness as blood pressure drops.

Question 51

How do anaphylaxis symptoms progress as the reaction intensifies?

Answer 51

As the reaction progresses, individuals may experience difficulty breathing due to airway constriction and fluid leakage into the lungs, often accompanied by a sensation of throat or chest tightness and wheezing.

Question 52

What are the late-stage symptoms of anaphylaxis, indicating a life-threatening situation?

Answer 52

In severe cases, individuals become pale and sweaty due to severely low blood pressure (anaphylactic shock), eventually leading to collapse, unconsciousness, and potentially death if untreated.

Question 53

Describe the critical steps in managing anaphylaxis as an emergency.

Answer 53

The initial focus is on airway, breathing, and circulation: lay the patient down, administer high-flow oxygen, and provide intravenous fluids to support blood pressure.

Question 54

What is the primary medication used to treat anaphylaxis, and how does it work?

Answer 54

Intramuscular adrenaline (epinephrine) is the primary treatment, as it effectively counteracts both smooth muscle contraction (relieving airway constriction) and vasodilation, helping to restore blood pressure.

Question 55

Why is adrenaline administered intramuscularly in anaphylaxis?

Answer 55

Intramuscular injection provides a rapid yet controlled absorption of adrenaline, avoiding the potential cardiac risks of intravenous administration while ensuring faster action than subcutaneous injection.

Question 56

Beyond adrenaline, what additional medications may be used to manage anaphylaxis?

Answer 56

Intravenous antihistamines (e.g., chlorphenamine) provide additional histamine blockade, steroids help reduce later-stage inflammation, and bronchodilators (e.g., salbutamol) further relieve airway constriction.

Question 57

What is the role of EpiPens in anaphylaxis management?

Answer 57

EpiPens are auto-injectable devices containing a pre-measured dose of adrenaline for self-administration by individuals at risk of anaphylaxis, enabling prompt treatment before professional medical help arrives.