Immunology Flashcards
What factors contribute to the skin as an immune system
Structure - keratin layer and stratification
Cells - immune cells and keratinocytes
Cytokines, chemokines etc
Genetics
What is autoimmunity
When there is a reaction to host tissue
Leads to chronic inflammation
What can activate keratinocytes
UV light
Sensitisers - such as in allergic contact dermatitis
How do Langerhans cells trigger the immune response
The process antigens and migrate away from the epidermis to the lymph system to present them to T cells
What do Birbeck granules look like
Tennis rackets
What T cells are found in the epidermis
CD8+
What T cells are found in the dermis
CD4+ and CD8+
Where are T cells produces
Bone marrow
How does T cell activation and antigen recognition occur
Through interaction with the T cell receptor (TCR) and the Major Histocompatibility Complex (MHC)
Describe the function of Mast cells
Effectors of the IgE mediated response - allergy
IgE binding causes activation of mast cells and release of inflammatory mediators
The degranulate and release many mediators such as histamine, interleukins and TNF
What are MHC proteins
An identity tag protein that sticks out of every cell and allows the body to identify it as self
Can also show which proteins are present in the cell
If a cell lacks MHC it is attacked by the immune system
Describe MHC class 1 proteins
Found on almost all cells
Present antigens to cytotoxic T cells
Present endogenous antigens
Describe MHC class 2 proteins
Found on antigens presenting cells - B cells and macrophages
Present to Th cells
Present exogenous antigen
List 4 conditions that are associated with inappropriate immune responses
Psoriasis
Atopic and contact dermatitis
Bullous pemphigoid
Urticaria
List some features of autoimmunity
Lymphocyte abnormality
Genetic predisposition
Hormonal influence
Anatomical alteration
Which skin conditions are autoimmune
Vitiligo - melanocytes attacked by T cells
Psoriasis
SLE - autoantibodies are formed for your own DNA
What is a primary immunodeficiency
One of genetic causes - inherited defect
Can be specific or non-specific
What is a secondary immunodeficiency
One that is acquired
E.g. AIDS, Ageing, cancer, malnutrition, diabetes
What mediates a Type I hypersensitivity reactions
IgE antibodies
Describe how type I hypersensitivity begins
Early exposure to the antigen causes the production of IgE
This binds to receptors on mast cells
On second exposure the receptors are rapidly activated and the mast cell degranulates - causing the allergic reaction
What mediates type II and III hypersensitivity reactions
IgG and IgM antibodies
Where is type II hypersensitivity significant
Autoimmunity and transplantation
Haemolytic disease of the newborn
Blood transfusion
What mediates a type IV hypersensitivity reaction
Th1 cells
They recruit other cells to the site, hence the delayed response
Which factors affect the skins immune response
Organ transplants - immunosuppressed
UV - damages structure
Ageing - change in structure, decreased effectiveness of immune system
What is the definition of hypersensitivity
Immune response that causes collateral damage to self
Exaggerated immune response
What is an allergy
Hypersensitivity disorder of the immune system
A persons immune system reacts to normally harmless substances
Allergy is declining in the UK true/false
False
It is on the increase
Describe a type 1 allergy
Immediate reaction - within minutes to 2 hours
Consistent reaction with every exposure
What is the clinical presentation of an allergy
Urticaria - itchy rash
Angioedema
Wheezing - asthma
Anaphylaxis
Describe urticaria
A very itchy rash
Forms hives or weals
Usually appears within one hour of allergen exposure and lasts a few hours
What is angioedema
localised swelling of mucous membrane or subcutaneous tissue
Face and lips
What is anaphylaxis
Life-threatening hypersensitivity reaction
Characterised by rapidly developing issues
Involves the airways closing, due to oedema, bronchospasm, hypotension, tachycardia etc
How can you investigate allergy
HISTORY!! IgE blood test Skin prick test Patch test - for contact Challenge test Check serum mast cell tryptase levels during anaphylaxis
What is the skin prick test
Introduce allergen via small needle in the skin
Cheap and quick results
Good specificity and sensitive
What is the challenge test
The patient is directly exposed to the allergen
e.g. wear latex gloves or eat peanut butter
Only done in clinical setting if anaphylaxis risk is low
What is the management of allergy
Allergen avoidance Education May wear alert bracelet Step 1 - anti-histamine Step 2 - corticosteroids Step 3 - epi-pen
What are non-allergic reactions
Non IgE mediated Mast cell granulation is directly caused - e.g. by drugs Can be metabolic - lactose Can be caused by toxins Coeliac disease
Describe type IV hypersensitivity
Delayed reaction - 24-48 hours after exposure
Antigen specific
mediated by T cells
often a contact dermatitis
How do you test for allergic contact dermatitis
Patch test
Common allergens are places into small discs and stuck to the back with hypoallergenic tape
Then left for 48 hours and taken off
Assess reaction after 48 and 96 hours to look for allergic reaction - positive result is a red or pink, itchy, often raised area at the site
Tells you which allergen is the cause
What is irritant contact dermatitis
Not an immunological process
Contact with irritant agents causes skin irritation
Doesn’t need previous sensitisation
Examples: Nappy rash (urine) and lip lick dermatitis (saliva)
