Immunology Flashcards
Type 1 allergy
- Time frame?
- Routes of exposure?
- Does the reaction vary?
- Pathophysiology?
Type 1 allergy typically produces an immediate reaction which occurs within minutes, or up to 2 hours after exposure to the allergen. Routs of exposure – skin contact, inhalation, ingestion and injection. There is consistent reaction with every exposure.
In type 1 allergy the allergy is picked up by allergen presenting cells e.g. dendritic cells which stimulates T cells which produce B cells which are specific to IgE, which bind the allergen to mast cells.
Describe the clinical presentation of type I hypersensitivity
- Urticaria – very itchy lesions which appear within 1 hour and last 2-6 hours. This is sometimes described as “hives”, “wheals”, “rash” etc
- Angioedema – localized swelling of subcutaneous tissue or mucous membranes which is non-pitting and not itchy (unless associated with urticarial
- Wheezing/asthma
- Anaphylaxis
What is the specific IgE test called?
RAST
Which test can you do in anaphylaxis?
Serum mast cell tryptase level
If skin prick testing is negative, but history is highly suggestive of allergy, then which investigation might you consider?
Challenge test - expose the patient directly to the allergen
Type IV allergy
- Why can it be difficult to identify?
- Pathophysiology?
- Give examples of some allergens
This is a delayed hypersensitivity, up to 24-48 hours, so can be difficult to identify.
Unlike type 1, which is mast cells mediated, this is T cell mediated and called allergic contact dermatitis. There a various routes of exposure, usually by direct skin contact e.g. perfumes.
Allergens include cosmetics, rubber accelarators, fragrances, plants, tattoos.
Type IV allergy
- Clinical presentation?
- Reaction on first 3 fingers of left hand?
- What does it resemble?
Clinical presentation is all about contact and exposure – the site and presentation depends on the allergen, e.g. nickel in belt buckle.
If the reactions is on the first three fingers on left hand, think garlic.
Although most of the time you get an eczematous reactions, you do get other types of inflammation with ACD. The picture opposite shows a lichenoid reaction to the gold crown.
What is the gold standard test for allergic contact dermatitis (type IV hypersensitivity)?
Patch testing
How is irritant contact dermatitis different to allergic contact dermatitis?
Examples of ICD?
By contrast to ACD, ICD is not immune mediated. Basically it is caused by the skin coming into contact with agents that abrade, irritate and traumatize the skin directly. It doesn’t not require prior sensitization and like ACD, the pattern also depends on exposure.
Examples include nappy rash and lip lick dermatitis.
ICD and ACD often coexist, and every occupation has its own fair share of allergens and irritants.
What are the four basic types of immune response?
- Normal Immune Response - infection controlled
- Hypersensitivity - overreaction to antigen
- Immunodeficiency - infection not controlled, tumours may form
- Autoimmunity - reaction to host tissue, chronic inflammation
Give four immunological features of the keratin layer in terms of immunology
- Sense pathogens via cell surface receptors and help mediate an immune response - keratinocytes can be activated by UV (sunlight) and sensitizers (e.g. allergic contact dermatitis)
- Produce antimicrobial peptides (AMPs) that can directly kill pathogens - AMPs have been found at high levels in skin of patients with psoriasis
- Produce cytokines and chemokines - recruit and regulate cells of the adaptive and innate immune system (e.g. in psoriasis)
Langerhans cells in the epidermis
- What type of cell?
- Function?
- Different types?
- A type of dendritic cell that intersperse with keratinocytes in the epidermis
- The main skin resident immune cell
- Different types of dendritic cells are localised in different skin compartments. They may have specific and distinct functions
T cells
- Which types are found where?
- Which ones are associated with which conditions? (TH1, 2, 17)
- Mainly CD8+ T cells are found in the epidermis
- CD4 + and CD8+ T cells are found in the dermis
- Other subsets of T cells (e.g. Natural Killer (NK) cells) are also found
- TH1: psoriasis
- TH2: atopic dermatitis
- TH17: psoriasis and atopic dermatitis
Where are T cells produced?
T cells are produced in the bone marrow and sensitized in the thymus.
Which T cells are helpers and which are cytotoxic?
Helper T cells = CD4+ Cytotoxic T cells = CD8+
