Immunology Flashcards
What is an allergy?
A hypersensitivity response to a protein (antigen) which is then known as an allergen.
Atopy refers to the predisposition of having hypersensitivity reactions to allergens i.e. the tendency to develop hayfever, eczema, asthma and food allergies.
Skin sensitisation theory for allergen development:
(1) Break in the skin i.e. cut/eczema where the allergen passes the skin barrier- immune system recognises it as foreign so when it is ingested get a full immune response.
(2) Lack of exposure to the allergen from the GI tract- when being weaned off food, from 6 months of age, if the baby is not exposed to certain allergens, their immune system will not recognise it as foreign when later ingested.
What are the types of hypersensitivity reactions? (RECAP)
Type 1- IgE mediated. Exposure to allergen trigger mast cells and basophils to release cytokines and histamines. This gives an immediate reaction as with food allergy.
Type 2- IgG or IgM mediated. Allergen activates compliment leading to direct damage of local cells i.e. haemolytic disease of the new-born or transfusion reactions.
Type 3- Immune complex accumulates and causes damage to local tissues i.e. RA or SLE
Type 4- Inappropriate activation of T-cells causing local tissue damage i.e. organ transplant rejection, contact dermatitis etc.
How are allergies investigated?
Can diagnose on a really good Hx.
Investigations include:
Skin prick test
RAST
Food challenge
Skin prick (compare to both saline and histamine control) and RAST (measure blood IgE levels- would be high for everything if the pt has asthma or eczema) test for sensitisation and so are not accurate in diagnosing an allergy. Food challenge is the gold standard- increasing the exposure of the food allergen to the patient and monitoring the response. i.e. start off with the allergen mixed with other food, then increasing the quantities.
Patch test- most accurate for diagnosing contact dermatitis. Place patch with the allergen for 2-3 days then remove to see the response.
How are allergies managed?
Establish allergen
Avoid allergen
If dust mite ensure hovering and changing sheets often
If hay fever stay indoor with high pollen count
Take prophylactic anti-histamine when trigger is inevitable
Carry EpiPen if risk of anaphylaxis
Some places may allow for gradual exposure to the allergen- immunotherapy.
If exposed to the allergen:
Antihistamines and steroids- dampen immune response
Adrenaline- if anaphylaxis.
After an allergic reaction, monitor closely in case anaphylaxis develops.
What is anahylaxis?
How is it managed?
A severe type 1 hypersensitivity reaction where there is massive mast cell degranulation, leading to compromise of airway, breathing or circulation.
Presentation: Urticaria Itching Angioedema Abdominal pain
Also- Laryngeal oedema (stridor), wheeze, SOB, tachycardia, collapse, light-headedness etc.
Management:
A- Secure airway- can give salbutamol
B- Oxygen if desaturated
C- IV fluids
D- Lie down to ensure cerebral perfusion
E- Look for urticaria, flushing and angioedema.
Once A-E then give Intramuscular adrenalin (can be repeated after 5 mins), antihistamines and steroids.
Need to measure the Tryptase levels (released by mast cells) within 6 hrs to confirm an anaphylaxis. Admit the child to paediatric unit since anaphylaxis is usually biphasic, and ensure family are aware of how to use EpiPen and administer BLS.
What are the indications for an Epipen?
All children and adults with anaphylactic reactions.
Also in generalise allergic reactions w/o anaphylaxis if:
Adolescent
Asthma requiring steroids
Nut/bee sting allergy
Poor access to medical treatment i.e. rural
Significant co-morbidities i.e CVD
What is allergic rhinitis?
How is it managed?
Type 1 hypersensitivity reaction to environmental allergens. These include house dust mites, pets, pollen/grass etc.
Presentation:
Runny, itchy, blocked nose
Sneezing
Red, itchy swollen eyes
Can be seasonal (hay fever), perinneal (all-year round) or occupational.
Management:
Avoid triggers- stay indoors when high pollen count
Hoover and change sheets regularly
Don’t keep pets
Can take antihistamines, nasal corticosteroids (fluticasone) or nasal antihistamines to instantly relieve symptoms.
NB Nasal spray should be held with opposite hand to the nostril, do not inhale whilst spraying as will reach back of throat. If can taste in back of throat then has gone too far.
What is Cows Milk Protein Allergy?
How does it present?
Allergic reaction to the protein found in Cow’s Milk. Can either be IgE mediated- symptoms come within 2hrs, or non-IgE mediated where they can develop over days.
NB lactose intolerance- can’t tolerate lactose (sugar not protein therefore not an allergen). Cow’s Milk intolerance is not an allergy.
GI symptoms: Abdominal pain Bloating and wind Diarrhoea Vomiting
Allergic symptoms: Urticaria Angioedema Cough Wheeze Sneezing Watery eyes Severe- anaphylaxis
How is Cow’s Milk Protein Allergy managed?
Diagnose based on Hx and examination, can use skin prick test but not needed.
(1) If breastfeeding- ask the mother to stop eating dairy products as they can react to the CMP.
(2) Give hydrolysed formula milk- where the CMP has already been broken down. In more sensitive cases babies require amino acid based formulas (elemental formulas).
Will outgrow by 3 years old. Can test the baby on the first step of the milk ladder (malted milk biscuits) every 6 months and progress up the ladder until symptoms develop.
What is Cow’s Milk intolerance?
Cow’s Milk Intolerance will present with the same GI symptoms as CMPA but without the allergic symptoms.
They will continue to thrive and grow, will just be intolerant of the milk (will still be able to drink it). they will outgrow the intolerance by 2-3yrs old, should be switched to breast milk or hydrolysed formula milk.
Can start the first step of the milk ladder at age 1yrs old.
When would recurrent infections in an infant warrant further investigations?
Usually common for children to have 4-8 respiratory infections per year.
Consider investigations-
Chronic diarrhoea since birth
More than usual amount of infections
Appearing unusually well I.e. afebrile with a massive pneumonia
Unusual infections I.e. candida, pneumocystis jiroveci, cytomegalovirus
Failure to thrive
What investigations are conducted with recurrent infections?
FBC- low neutrophil can indicate phagocytic disorder, low lymphocytes can indicate T-cell disorder.
Immunoglobulins- abnormal can indicate B-cell disorder
Antibodies to vaccines
CXR to look for scarring of lung from previous RTI
CT chest for bronchiectasis
Sweat Test for CF
Complement test- for complement disorder
HIV test if clinically relevant
What is severe combined immunodeficiency syndrome? (SCID)
How does it present?
How is it managed?
X-linked recessive disease leading to the absence or dysfunctioning of B and T cells.
Presentation- Diarrhoea since birth Opportunistic infections I.e. pneumocystis and cytomegalovirus Failure to thrive Unwell after live vaccinations Omenn syndrome
Management- Reducing opportunistic infection- sterile environment Avoiding live vaccinations Immunotherapy Treat underlying conditions Haemopoetic stem cell transplant
What is selective IgA immunodeficiency?
Abnormal B cells lead to a deficiency of IgA. This is responsible for secretions of the GI tract, respiratory tract, salivary glands etc and is useful in protecting against opportunistic infections.
Mild immunodeficiency so patients are often asymptomatic.
When testing in coeliac test for IgA anti-TTG or anti-EMA, if person has IgA immunodeficiency then this will be low even if they have coeliac. Therefore test IgA first and if low test for IgG anti-TTG or anti-EMA.
What is common variable immunodeficiency?
Gene mutation in a component of B cell.
Patient has an IgG and IgA immunodeficiency +/- IgM. Therefore will get recurrent respiratory tract infections, will not develop immunity post infection/vaccine and develop chronic lung disease.
At risk of Non-Hodgkin lymphoma and RA.
Manage with immunoglobulin infusions and managing infections as they occur.
