Oral mucosa: Allergies Flashcards
(40 cards)
Define allergy
When immune system responds in an exaggerated or inappropriate way to an extrinsic (non-self) antigen
Define autoimmunity
When immune system responds in an exaggerated or inappropriate way to an intrinsic (self) antigen
Define hypersensitivity
When immune system responds in an exaggerated or inappropriate way resulting in harm
e.g. allergy and autoimmunity are forms of hypersensitivity
When does hypersensitivity occur?
Occurs on 2nd exposure to antigen
Is a characteristic of the individ (genetics involved)
Types of hypersensitivity?
Type I - immediate/anaphylaxis
II - cytotoxic
III - immune complex
IV - delayed
How is type IV hypersensitivity mediated?
Cell mediated
What hypersensitivities are antibody mediated?
I, II, III
Type I hypersensitivity features?
Anaphylaxis Rapid onset IgE mediated Antigen gives rise to type I hypersensitivity rxns Most allergens are small proteins
What does histamine release in type I hypersensitivity cause?
Vascular dilation (vasodilation)
Increased vascular permeability e.g. oedema
Bronchospasm
Urticarial rash
Increased nasal and lacrimal secretions = runny nose
What do type I hypersensitivity reactions most commonly present as?
Hayfever
Asthma
Acute allergic rxns
Angio-oedema/anaphylaxis e.g. penicillin, latex allergies
How to diagnose type I hypersensitivities?
Wheel and flare skin test
Apply small amount of allergen under skin using prick test
Wheel caused by extravasation of serum into skin due to histamine e.g. angio-oedema
Flare caused by axon reflex
Late phase 6hrs plus due to leukocyte infiltrate and more oedema
How to manage type I hypersensitivities?
Adrenaline
Antihistamines
Corticosteroids
Avoidance of allergen
Type II hypersensitivity features?
Antibodies target self antigens (auto-antibodies)
Usually IgG or IgM
Antibodies induce cell damage and inflammation
Auto-antibodies activate either Antibody dependent cell cytotoxicity (ADCC) OR complement
What does complement activation in type II hypersensitivity result in?
Inflammation Cell death (membrane attack complex)
What are type II hypersensitivity responses important in?
Acute transplant rejection
Autoimmune diseases
- Pemphigus
- Pemphigoid
Type III hypersensitivity features?
Immune complex forms between antibodies and antigens
What can immune complexes in type III hypersensitivity deposit in?
The lining of BVs
Glomeruli
Lung
What can immune complexes in type III hypersensitivity induce?
Complement activation
Neutrophil binding
= Inflammation and vascular permeability
What are type III hypersensitivity reactions important in?
Immune complex mediated vasculitis e.g. erythema multiforme, systemic lupus erythematosus (SLE)
Type IV hypersensitivity features?
Cell mediated - generally localised
Mediated by T cells
Slow to develop, resolve
Localised
Type IV hypersensitivity - what are they important in?
Delayed hypersensitivity responses
Contact dermatitis
Lichenoid reactions to amalgam fillings
Oral lichen planus
How does type IV hypersensitivity occur?
Langerhan’s cells form a network within the epithelium
They intercept and process antigen entering the mucosa
The antigen stimulates keratinocytes to release TNF
= Stimulates langerhan’s cells to migrate to the draining lymph nodes
Langerhan’s cells process than antigen
And present parts of it to T cells circulating though the lymph node
Antigen specific T cells become activated
Proliferate of antigen specific T cells (clonal expansion)
Cytotoxic T cells (CD8) kill basal karatinocytes (apoptosis)
How do T cells kill keratinocytes?
They induce apoptosis by:
Fas/fas-ligand mediated apoptosis
Perforin/granzyme B
What is increasing in the population?
Large increase in children with asthma
and allergic responses in adults
= allergies increasing in dental surgery - latex and dental materials
