Week 3 (Part 1): Hypersensitivity I Flashcards
Define hypersensitivity reaction:
It’s when the immune system goes wrong!
- Hypersensitivity refers to sensitization of the immune system by repeated exposure to an allergen
- Hypersensitivity disorders refer to excessive or inappropriate activation of the immune system
How many types of hypersensitivity reactions are there?
- Describe each
Historically they have been subdivided into 4 types:
- type I which is an IgE-mediated response;
- type II antibody-mediated response, specifically IgG and IgM;
- type III reactions are complement-mediated immune responses;
- type IV are referred to as T-cell-mediated responses.
What are antigens usually referred to as?
- Are they harmful?
Allergens
- Allergens are generally harmless environmental antigens that you can see listed in the tables provided in this slide.
- Most people are able to inject, or touch, or breath in these materials and the immune system does not create a response to them.
What does an antigen become harmful?
In susceptible individuals, the immune system overreacts and causes what we tend to call ”an allergic reaction” or “allergies”
What is atopy?
- What are they likely to develop?
- What is it associated with?
The individuals that have IgE mediated responses tend to have what we refer to as Atopy.
- Atopyrefers to the genetic tendency to develop allergic diseases such as allergic rhinitis, asthma andatopicdermatitis (eczema).
- Atopyis typically associated with heightened immune responses to common allergens, especially inhaled allergens and food allergens.
People with one atopic condition are more [likely or less likely] to develop another atopic condition?
More likely
What is the allergic march?
characterized by a typical sequence of immunoglobulin E (IgE) antibody responses and clinical symptoms which may appear early in life, persist over years or decades, and often remit spontaneously with age.
What is the onset of hypersensitivity I reactions?
Type I hypersensitivity reactions begin rapidly, often within minutes of an antigen challenge.
What are the 4 routes of exposure?
Exposure to the allergen can be through inhalation, ingestion, injections, or skin contact
What is the first exposure?
- Explain it
First exposure to allergen is called sensitization → produce IgE Abs to the allergen
- Allergen is met by phagocytic cell that ingests it and releases an antigen presenting cell
- Cascade where B-cell created that secretes IgE
IgE becomes bound to mast cells
- A “sensitized” person has allergen-specific IgE Abs bound to mast cells.
Symptoms experienced by the host at this point are mild or negligible
What is re-exposure?
Re-exposure to the same allergen = memory response occurs immediately allergen-IgE binding activates the mast cell to “degranulate” - releases histamine and cytokines, get atopic symptoms
The outcomes of histamine production with re exposure are our classic known symptoms of …
… sneezing, mucus secretion, contraction of smooth muscle in asthma bronchospasm and inflammation of endothelial cells causing vasodilation and increased permeability of blood vessels.
Depending on the poral of entry type I reactions may occur as a local or atopic reaction that is (2) …
… merely annoying (ie seasonal allergies) or severely debilitating (asthma) or as a systemic and potentially life-threatening reaction (anaphylaxis)
What is anaphylaxis?
It is a systemic life-threatening hypersensitivity reaction characterized by widespread edema, vascular shock secondary to vasodilation, and dyspnea
ANAPHYLAXIS IS A MEDICAL EMERGENCY
- It is a severe, potentially
life-threatening allergic reaction
What provokes anaphylaxis?
- How does it usually enter the body?
Anaphylaxis is provoked by any allergen that enters the bloodstream
- injected directly into blood, insect sting or rapid absorption across the epithelial surface of the skin or in gut
The level of severity of anaphylaxis depends on…
… the level of previous sensitization.
- Even small amounts of antigen, such as residual amounts of peanuts that remain on equipment used for preparing foods with peanuts in them can be sufficient to cause anaphylaxis.
- In fact, I have had patients that have experienced anaphylactic reactions from the mere smell of peanuts.
What happens minutes after exposure during anaphylaxis ?
Within minutes after exposure, itching, hives, and skin erythema develop, followed shortly by bronchospasm and respiratory distress
- Vomiting, adominal cramps, diarrhea, and laryngeal edema and obstruction follow, and the person may go into shock and die within the hour which tends to be from
What does anaphylactic shock do in relation to blood pressure?
Anaphylactic Shock which is a catastrophic loss of blood pressure due to extensive fluid loss from blood vessels.
How can anaphylaxis be temporarily controlled? Why?
Temporarily controlled by epinephrine injection (EPIPEN); Epinephrine rapidly increases blood pressure by causing vasoconstriction & relaxing smooth muscle cells.
What types of allergens make up anaphylaxis?
75% - food
17% - inhaled substances
4% - wasp venom
Rest assured that the risk of anaphylaxis to an allergen is generally extremely low with ___% people experiencing IgE mediated allergies have only mild systemic reactions
99.9%
Diagnosis of allergies?
1) Blood - Increased serum IgE levels
2) Skin Prick Test or Skin Patch Test
3) Biopsies during endoscopies and colonoscopies
- GI related intolerances looking for IgE in the biopsied tissue
What is allergy immunotherapy?
- How does it work?
Also known as allergy shots, is a form of long-term treatment that decreases symptoms for many people with allergic rhinitis, allergic asthma, conjunctivitis (eye allergy) or stinging insect allergy
How does allergy immunotherapy work?
Allergy shots worklike avaccine
- Your body responds to injected amounts of a particular allergen, given in gradually increasing doses, by developing immunity or tolerance to the allergen.
- The principle is to divert the immune response away from an IgE mediated response to an IgG response to lessen symptoms over time
What are risks to allergy immunotherapy?
Most people don’t have much trouble with allergy shots.
But they contain the substances that cause your allergies — so reactions are possible, and can include:
1) Local reactions,which can involve redness, swelling or irritation at the injection site.
- These common reactions typically begin within a few hours of the injection and clear up soon after.
2) Systemic reactions,which are less common — but potentially more serious.
- You may develop sneezing, nasal congestion or hives.
- More-severe reactions may include throat swelling, wheezing or chest tightness.
3) Anaphylaxisis a rare life-threatening reaction to allergy shots.
- Anaphylaxis often begins within 30 minutes of the injection, but sometimes starts later than that.
- Which again is why this is given within health care facilities, and patients are monitored for at least 30 minutes post injection.
