Immunology Flashcards
What is atopy
Predisposition to having a hypersensitivity reaction to an allergen
Eczema, asthma, hay fever, allergic rhinitis, food allergies
What is a type 1 allergic reaction
IgE antibody mediated
Triggers mast cells and basophils to release histamine and cytokines
Immediate reaction
Itching, facial swelling, urticaria, anaphylaxis
What is a type 2 allergic reaction
IgG and IgM mediated
Activation of complement system
Direct damage to local cells
Haemolytic disease of the newborn, transfusion reactions
What is a type 3 allergic reaction
Immune complex mediated
Damage to local tissue
SLE, rheumatoid arthritis
What is a type 4 allergic reaction
Cell mediated
T cells inappropriately activated
Inflammation and damage to local tissue
Organ transplant rejection, contact dermatitis
What are the investigations for allergies
Detailed history
Skin prick test
RAST test (blood test for total and specific IgE, assesses for sensitisation)
Food challenge test (gold standard, in specialised unit, gradually increase quantity of food)
Patch testing (for allergic contact dermatitis)
What is the management for allergic reactions
Identify correct allergen
Avoidance
Regular hoovering and changing sheets
Stay indoors when pollen count high
Prophylactic antihistamines
Adrenaline auto-injector
Antihistamines, steroids (oral prednisolone, IV hydrocortisone), IM adrenaline
What is anaphylaxis
Life threatening medical emergency
Severe type 1 hypersensitivity reaction
IgE stimulates mast cells to release histamine and other cytokines
Rapid onset
How might a patient with anaphylaxis present
Urticaria
Itching
Angio-oedema
Abdominal pain
Shortness of breath
Wheezing
Stridor
Tachycardia
Lightheadedness
Collapse
What is the management for anaphylaxis
Call for help early
ABCDE
IM adrenaline (repeat after 5 minutes)
Antihistamines (oral chlorpheniramine or cetirizine)
Steroids (IV hydrocortisone)
Assessment after episode
Confirm with serum tryptase (within 6 hours)
Education
Give parents BLS training
What are the indications for having an adrenaline auto-injector
Anaphylactic reaction
Generalised allergic reactions with risk factors (asthma needing steroids, poor access to medical treatment, adolescents, insect sting allergies, significant comorbidities)
What is allergic rhinitis
IgE mediated type 1 hypersensitivity reaction
Triggers: tree pollen, grass, house dust mite, pets
Can be: seasonal, year round, occupational
Associated with personal or family history of atopy
How might a patient with allergic rhinitis present
Runny, blocked, itchy nose
Sneezing
Itchy, red, swollen eyes
What is the management for allergic rhinitis
Avoid triggers
Hoover and change pillows regularly
Good ventilation in home
Stay indoors when pollen count high
Oral antihistamines
Nasal corticosteroid spray
Nasal antihistamines
What are some non-sedating antihistamines
Cetirizine
Loratadine
Fexofenadine
What are some sedating antihistamines
Chlorphenamine (piriton)
Promethazine
What is Cow’s milk protein allergy
In infants and children under 3
IgE mediated (within 2 hours)
Non-IgE mediated (over several days)
More common in formula-fed babies
How might a baby with Cow’s milk protein allergy present
Bloating
Wind
Abdominal pain
Diarrhoea
Vomiting
Urticarial rash
Angioedema
Cough
Wheeze
Sneezing
Watery eyes
Eczema
Possible anaphylaxis
What is the management for cow’s milk protein allergy
Skin prick test (not always needed)
Avoid cow’s milk (breastfeeding mothers avoid dairy, switch formula)
Every 6 months, try stepping up milk ladder (gradually build up to a normal diet)
When would you refer a child to a specialist for recurrent infections
Chronic diarrhoea since infancy
Failure to thrive
Unusually unwell
Significantly more infections than expected
Unusual or persistent infections (cytomegalovirus, candida)
What are the investigations for recurrent infections
FBC
Immunoglobulins
Complement protein
Antibody response
HIV test
Chest X-ray
Sweat test
CT chest
What is severe combined immunodeficiency
Children have almost no immunity to infection
Absence or dysfunction of T and B cells
X-linked recessive
How might a patient with severe combined immunodeficiency present
Within first few months of life
Persistent severe diarrhoea
Failure to thrive
Frequent opportunistic infections
Unwell after live vaccines
Ommen syndrome
What is Ommen syndrome
Rare cause of SCID
Abnormally functioning and downregulated T cells
Presentation: red scaly dry skin, hair loss, diarrhoea, failure to thrive, lymphadenopathy, hepatosplenomegaly
What is the management for severe combined immunodeficiency
Fatal unless successfully treated
Treat underlying infections
Immunoglobulin therapy
Sterile environment
Avoid live vaccines
Haematopoietic stem cell transplant
What is selective immunoglobulin A deficiency
Most common immunoglobulin deficiency
Low IgA (normal IgG and IgM)
Asymptomatic if mild
If severe, recurrent mucous membrane infections
What is common variable immunodeficiency
Genetic mutation in the genes coding for components of B cells
Deficiency in IgA and IgG
Recurrent respiratory tract infections
Unable to develop immunity (to infections or vaccines)
Prone to rheumatoid arthritis and non-Hodgkin’s lymphoma
Management: regular immunoglobulin infusion, treat infections as they occur
What is X-linked agammaglobulinemia
Abnormal B cell development
What is DiGeorge syndrome
A T cell deficiency
Developmental defect in 3rd pharyngeal pouch and 3rd branchial cleft
Incomplete development of thymus gland
Inability to create functional T cells
Clinical features: congenital heart disease, abnormal facial features, thymus incomplete, cleft palate, hypoparathyroidism, 22nd chromosome affected
What is purine nucleoside phosphorylase deficiency
A T cell deficiency
Autosomal recessive
Immunity gradually gets worse (very susceptible to infection)
What is Wiskott-Aldrich syndrome
X-linked recessive
Abnormally functioning T cells
Get: thrombocytopenia, immunodeficiency, neutropenia, eczema, recurrent infections, chronic bloody diarrhoea
What are complement disorders
Recurrent infections with encapsulated bacteria (Haemophilus influenza B, streptococcus pneumoniae, neisseria meningitidis
