Hypersensitivity Flashcards
(37 cards)
Define hypersensitivity, give an example
Allergy or autoimmunity, e.g. asthma and allergic diseases (increasing in pop)
Why is hypersensitivity an issue in dentistry?
More people sensitive to latex, dental materials, drugs
What does acquired immunity consist of?
Antibody response (humoral) and cell mediated response = involved in hypersensitivity rxns
Features of antibody response?
Occurs quickly
Systemic or widespread
Bcos antibodies are soluble proteins that reach most parts of the body quickly by blood, tissue fluid and body secretions
What is cell mediated immunity directed against?
Tumour cells, virally transformed cells and foreign cells
What do cellular immune responses tend to be?
Localised, slow to develop and slow to resolve
How can the immune system fail?
Hypersensitivity = failure of immune system
Fail to produce adequate immune response - immunodeficiency
Produce an overactive, damaging response -hypersensitivity - allergy
What is hypersensitivity?
= failure of immune system
Immune system responds in exaggerated or inappropriate way = harm caused
Usually occurs on 2nd or subsequent exposure to antigen
Genetic susceptibility
Name the 4 types of hypersensitivity
- Immediate/anaphylaxis
- Cytotoxic
- Immune complex
(1-3 = antibody mediated) - Delayed = cell mediated
Features of immediate (1) hypersensitivity
Acute (anaphylaxis)
Rapid onset
IgE mediated
How does immediate hypersensitivity work?
- Allergen exposure
- T cells bind to allergen (Antigen presenting cell)
- T cell differentiates into Th2
- Th2 = antibody production, release IL4
- High IL4 = increase IgE from plasma cell = more humoral response
- Mast cells and basophils express FcE receptors and contain histamine granules
- IgE in plasma bind to receptors on mast cells
- = Sensitisation = IgE produced
- 2nd exposure to allergen
- Clusters form and mast cells degranulate and secret IL5
- Eosinophils attracted = mass cell release of histamine
Who is susceptible to type 1 hypersensitivity? What is an allergen?
High IgE levels
Allergen = Ag that gives rise to type 1 hypersensitivity - most are small proteins e.g. pollen - grass
Cellular response of type 1?
Mast cell and basophils expressed FcE receptors and contain histamine granules
IgE in plasma binds to receptors
Allergen exposure
Sensitisation = IgE prodcued
2nd exposure to allergen = IgE binds to allergen
Clusters form and mast cell degranulates and secretes IL-5 = attracts eosinophils = mass release of histamine
What does histamine release cause?
Vascular dilation Increase vascular permeability e.g. oedema Bronchospasm Urticarial rash Increase nasal and lacrimal secretions
What does type 1 hypersensitivity most commonly present as?
Hay fever, asthma, acute allergic response - angio-oedema/anaphylaxis
Diagnosis - wheel and flare skin test?
Apply allergen under skin using prick test - response within 5 mins
Wheel caused by extravasation of serum into skin due to histamine - angio-oedema
Flare (red patch) due to axon reflex
Late phase (6hrs plus) due to leukocyte infiltrate and more oedema
How to manage type 1 hypersensitivity?
Adrenaline, antihistamines, corticosteroids, avoidance of allergen
Features of type 2 hypersensitivity
Antibody mediated - antibodies target cell surface self antigens (auto-antibodies)
- Usually IgG or IgM
- Antibodies induce: cell damage, inflam
Type 2 - what do autoantibodies activate?
What are type 2 rxns important in?
ADCC, complement
Important in: - Acute transplant rejection / blood transfusion - Haemolytic Disease of the Newborn - Autoimmune diseases e.g. Pemphigus Pemphigoid
What does complement and ADCC activation in type 2 result in?
Inflammation and cell death (by membrane attack complex)
ADCC = inflam, cell death
Haemolytic disease of newborn - type 2 hypersensitivity?
- First Pregnancy - RhD+ baby’s blood enters RhD- mother’s circulation
- Baby born BUT mother
raises Ab to RhD - Second Pregnancy – If
foetus is RhD+ mother
IgG crosses placenta and
will destroy foetal
erythrocytes - SO – preformed anti-RhD Ab given to Rh- mothers after delivery of RDH+ infants
What is pemphigus? (type 2)
Auto-antibodies against desmoglein-1 and 3
Ab prevents formation of gap junctions between epithelial cells
Epithelial shedding - mainly mucosal
What is pemphigoid? (type 2)
Auto-antibodies against hemidesmosomes
Ab prevents binding of epi with dermis at basement membrane
Epi shedding - skin and mucosal
Type 3 hypersensitivity?
Immune complex - mediated hypersensitivity
Immune complexes form between antigen and antibodies
These complexes form in the serum
Diff to type 2 which are cell based
