Immunology 1: Hypersensitivity and allergy Flashcards by Kieron Young

Describe an appropriate immune reaction

Immune responses occur to foreign harmful agents e.g viruses, bacteria. etc. Antigen recognition by cells of the immune system –> antibody production

Immune response will:

Eliminate pathogens
may cause tissue damage as a side effect (but as long as the pathogen is eliminated it will be repaired easily

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What is a hypersensitivity reaction?

Occurs when immune responses are mounted against:

Harmless foreign antigens (allergy, contact hypersensitivity)
Autoantigens (autoimmune diseases)
Alloantigens (serum sickness, transfusion reactions, graft rejection.

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What are the classifications of hypersensitivity reactions?

Type I: Immediate Hypersensitivity
Type II: Antibody-dependent Cytotoxicity
Type III: Immune Complex Mediated
Type IV: Delayed Cell Mediated

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Give examples of type I hypersensitivity reactions

Type I: immediate hypersensitivity

Anaphylaxis
Asthma
Rhinitis
Seasonal
Perennial
Food Allergy

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Describe primary antigen exposure in type I hypersensitivity?

Sensitisation not tolerance
IgE antibody production
IgE binds to Mast Cells & Basophils

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Describe secondary antigen exposure in type I hypersensitivity?

More IgE Ab produced
Antigen cross-links IgE on Mast Cells/Basophils
Degranulation

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What are the two types of type II hypersensitivity?

Organ specific autoimmune disease

Myasthenia gravis (Anti-acetylcholine R Ab)
Glomerulonephritis (Anti-glomerular basement membrane Ab)
Pemphigus vulgaris (Anti-epithelial cell cement protein Ab)
Pernicious anaemia (Intrinsic factor blocking Abs)

Autoimmune cytopenias

Haemolytic anaemia
Thrombocytopenia
Neutropenia

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How do you test for specific autoantibodies?

This is used for type II hypersensitivity

Immunofluoresence
ELISA eg anti-CCP (Cyclic Citrullinated Peptide Abs for Rheumatoid Arthritis)

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Describe the process of the type III hypersensitivity

Formation of Antigen-Antibody complexes in blood
Complex deposition in blood vessels/tissue
Complement & cell activation
Activation of other cascades eg clotting
Tissue damage (vasculitis)
1) Systemic lupus erythematosus (SLE)
2) Vasculitides (Poly Arteritis Nodosum, many different types)

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Type III Immune Complex Mediated Hypersensitivity
Slide 15

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Give examples of type IV hypersensitivity responses?

Chronic graft rejection
GVHD
Coeliac disease
Contact hypersensitivity
Many autoimmune diseases….
Asthma
Rhinitis
Eczema

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What are the three main varieties of type IV delayed hypersensitivity responses?
Describe the mechanisms?

Th1
Cytotoxic
Th2

Transient/Persistent Ag
T cell activation of macrophages, CTLs
Much of tissue damage dependent upon TNF & CTLs

See slides

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How does inflammation arise?

Common feature of immune responses

Immune cell - recruited to sites of injury and/or infection. Activated
Inflammatory mediators - Complement, cytokines etc.

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What are the features of inflammation?

Vasodilatation, increased blood flow
Increased vascular permeability
Inflammatory mediators & cytokines
Inflammatory cells & tissue damage

Signs:

redness
heat
swelling
pain

Inflammatory cell infiltrate
Cell trafficking – chemotaxis
(Neutrophils, macrophages, lymphocytes, mast cells)
Cell activation

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What causes the increased vascular permeability in inflammation?

C3a, C5a, histamine and leukotrienes

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What cytokines are released in inflammation?

IL-1, IL-6, IL-2, TNF, IFN-gamma

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What chemokines are released in inflammation?

IL-8/CXCL8, IP-10/CXCL10

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What are the risk factors for allergy?

Genetic and environmental

Genetic - polygenic.
Genes on IL-4 gene cluster = raised IgE, asthma, atopy
Genes on chr. 11q (IgE receptor) = Asthma and atopy
Genes linked to structural cells = eczema

Environmental:

Age
Gender
Family size
Infection
Animals
Diet

Allergy risk in the UK is increasing.

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What are the levels of allergy severity?

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Mild occasional symptoms
Chronic asthma
Life threatening anaphylaxis

What are the types of inflammation in allergy?

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Anaphylaxis, urticaria, angioedema
type I hypersensitivity (IgE mediated)
Idiopathic/chronic urticaria
type II hypersensitivity (IgG mediated)
Asthma, rhinitis, eczema:
mixed inflammation:
1) type I hypersensitivity (IgE mediated)
2) type IV hypersensitivity (chronic inflammation)

What does the expression of disease require?

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Development of sensitisation to allergens instead of tolerance (primary response - usually in early life)
Further allergen exposure to produce disease (memory response - any time after sensitisation)

Define atopy

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Atopy refers to the genetic tendency to develop allergic diseases such as allergic rhinitis, asthma and atopic dermatitis (eczema).

Describe the sensitisation of atopic airway disease?

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See slides

What do eosinophils contain?

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Large granules –> toxic proteins

Leads to tissue damage. They are recruited to allergic inflammation

Describe mast cells

Tissue resident cells IgE receptors on cell surface Crosslinking of IgEs leads to mediator release Pre-formed - histamine - cytokines - toxic proteins Newly synthesized - leukotrienes - prostaglandins

What allergies are neutrophils important in?

virus induced asthma severe asthma atopic eczema

What do the granules of neutrophils contain and what can they synthesize?

Digestive enzymes Synthesize: - oxidant radicals - cytokines - leukotrienes

Define acute asthma?

Acute inflammation of the airway: Mast cell activation & degranulation Pre stored mediators released: - histamine Newly synthesised mediators - prostaglandins, leukotrienes Acute airway narrowing

What is the two-phase response to single allergen challenge?

See slides

Describe the immunopathogenesis of chronic asthma

Chronic inflammation of the airways. 1) Cellular infiltrate - Th2 lymphocytes, eosinophils 2) Smooth muscle hypertrophy 3) Mucus plugging 4) Epithelial shedding 5) Sub epithelial fibrosis

Clinical features of asthma

``` Reversible generalised airway obstruction Chronic episodic wheeze Bronchial hyperresponsiveness Bronchial irritability Cough Mucus production Breathlessness Chest tightness ``` Response to treatment Spontaneous variation Reduced & variable peak flow (PEF)

Describe allergic rhinitis

Seasonal - hay fever - grass, tree pollens Perennial - perennial allergic rhinitis - HDM, pets Symptoms: - sneezing - rhinorrhoea - itchy nose, eyes - nasal blockage, sinusitis, loss of smell/taste

Describe allergic eczema

- Chronic itchy skin rash - Flexures of arms and legs - HDM sensitisation and dry cracked skin - Complicated by bacterial and (rarely) viral infections (early childhood, herpes simplex) - 50% clears by 7 years - 90% by adulthood

Describe mild and severe food allergy

Mild - Itchy lips, mouth, angioedema, urticaria Severe - Nausea, abdominal pain, diarrhoea, collapse, wheeze Anaphylaxis

What can cause food allergies in infancy?

Egg, cows milk

What can cause food allergies in children/adults?

Peanuts, nuts, shell fish, fruits, cereals, soya

What is anaphylaxis?

Severe generalised allergic reactions. It is uncommon but potentially fatal. Generalised degranulation if IgE sensitised mast cells.

What are the symptoms of anaphylaxis?

- itchiness around mouth, pharynx, lips - swelling of the lips, throat and other parts of the body - wheeze, chest tightness, dyspnoea - faintness, collapse - diarrhoea & vomiting - death if severe & untreated

What systems are affected in anaphylaxis?

Cardiovascular - vasodilatation, cardiovascular collapse Respiratory - bronchospasm, laryngeal oedema Skin - vasodilatation, erythema, urticaria, angioedema GI - vomiting, diarrhoea

How do you investigate and diagnose allergies?

``` Careful history essential Skin prick testing RAST (blood specific IgE): Total IgE Lung function (asthma) ```

What is the emergency treatment of anaphylaxis?

EpiPen & Anaphylaxis kit - antihistamine, steroid, adrenaline - Seek immediate medical aid

How do you prevent anaphylaxis?

Avoidance of known allergen Always carry a kit & EpiPen Inform immediate family & caregivers Wear a MedicAlert® bracelet

How do you treat allergic rhinitis?

- anti-histamines (sneezing, itching, rhinorrhoea) - nasal steroid spray (nasal blockage) - cromoglycate (children, eyes) If severe: anti-IgE, anti-IL-4/-13, anti-IL-5 mAb

What is the treatment for Eczema?

- Emollients - Topical steroid cream# If severe: anti-IgE, anti-IL-4/-13, anti-IL-5 mAb

What is the asthma treatment plan?

See slide 47

Immunology 1: Hypersensitivity and allergy Flashcards

(45 cards)