Immunology Flashcards
Define sensitivity and hypersensitivity
Sensitivity: normal response to a stimulus
Hypersensitivity: reproducible symptoms or signs following exposure to a stimulus at a dose which is tolerated by normal people
Define allergen
any substance stimulating the production of IgE or a cellular immune response
Define sensitisation
production of IgE antibodies (detected by serum IgE assay) after repeated exposure to an allergen
Define atopy
A personal/ familial tendency to produce IgE antibodies in response to ordinary exposures to potential allergens, Strongly associated with asthma, rhinitis, conjunctivitis, eczema and food allergy
Define allergy
A hypersensitivity reaction initiated by specific immunological mechanisms, leading to disease. This can be IgE medicate or non- IgE mediated.
The developing immune system must be sensitised to an allergen before an allergic immune response develops.
Age is important to the history, e.g. eczema after the age of 2 is less likely to be allergic as they have been exposed to most allergens
Describe the pathophys of a IgE mediated immune response
- allergen binds to TH2 cell, which stimulated B cell to become plasma cell and produce IgE antibodies to that antigen
- on second exposure antigen binds to specific IgE
- leads to mast cell activation and degranulation
- this leads to release of:
- histamine (vasodilates, increases permeability, bronchoconstricts, mucus production)
- prostaglandins (bronchoconstricts)
- trypase
- leukotrienes
- IL-3,4,5 (cytokines)
How can adverse reactions to food be classified?
- immunological reactinons: can be either IgE mediated or non IgE mediated
- non immunological reactions
What questions should be asked in history of someone presenting with adverse food reaction?
- what foods
- what symptoms
- when do symptoms occur
- what age did it start (NOT MILK ALLERGY IF >1yr OLD)
- how much food needed to cause symptom
- do they occur every time they have that food
- how long do symptoms last
- is there phx or fhx of allergy/ atopy
- feeding history, age of weaning, formula vs breast
- have any exclusion diets been tried
- is their diet nutritionally sufficient
How should IgE mediated and non IgE mediated allergy be investigated
IgE: skin prick test, serum IgE assay, atopy patch testing and oral food challenges
Non IgE mediate: elimination diet to see if improved then reintroduce to see if returns
How do the features of IgE mediated and non IgE mediated allergy differ?
IgE mediated: symptoms start within 2 hrs of ingestion and go within 12. Can cause GI, resp, cutaneous or cardiac symptoms.
Non IgE mediated: presents hrs or days after ingestion and lasts for days. Usually only causes GI or cutaneous symptoms.
State the common IgE mediated allergens
- wheat
- sesame
- eggs
- milk
- soya milk
- kiwi
- seafood
- shellfish
- tree nuts
- peanuts
State the 4 common non IgE mediated allergens
- wheat
- eggs
- soya
- milk
What is anaphylaxis
A severe generalised or systemic hypersensitivity reaction characterised by being rapid in onset affecting 2 or more organ systems with potentially life-threatening airway, breathing or circulation symptoms
Describe the diagnostic criteria for anaphylaxis
Acute onset of an illness with involvement of the skin, mucosals tissue or both
AND AT LEAST 1 OF;
• Resp compromise (e.g. dyspnoea, wheeze bronchospasm, stridor, hypoxaemia)
• Reduced BP or associated symptoms of end organ dysfunction (e.g. syncope)
Give 5 symptoms of anaphylaxis
- Skin/ mucosal: itching lips/ tongue, lip/ tongue/ uvula swelling, skin flushing, itching, urticaria, angiodema
- Resp: stridor, SOB, tight chest, wheeze, cough, nasal itching and congestion, throat itching, hoarseness, cyanosis and resp arrest
- GI: abdo pain, nausea, vomiting, diarrhoea
- cardio: chest pain, tachy, brady, palpitations, hypotension, feeling faint, arrest
- CNS: altered behaviours, headache, dizzy, confused, feeling of impending doom
Give 3 unusual but possible presentations of anaphylaxis
- biphasic anaphylaxis: second reaction 4-12 hrs after initial reaction
- idiopathic anaphylaxis: diagnosed where no triggers can be found on hx and allergy tests are negative
- post prandial exercise induced: reaction requires food contact followed by exercise
give 5 common triggers for atopic eczema
- irritants eg soaps/ detergents
- environmental factors: cold/ dry weather, dampness, house dust mites, pet fur, pollen, moulds
- food allergies- cows milk, eggs, wheat, peanuts, soya
- wools and synthetic fibres
- skin infections
Describe the 3 types of allergic rhinitis
- Seasonal: occurs at certain times of the year, usually due to pollen
- Perennial (persistent): throughout the year, commonly die to dust or pets
- Occupational: due to exposure of allergens, e.g. latex gloves
Describe the pathophys of allergic rhinitis
An IgE mediated inflammation of the nasal mucosa following exposure to allergens. This causes histamine to be released in response.
• Acute phase response (mins): sneezing and increase in nasal secretions
• Late phase response (6-12hrs): characterised by nasal obstruction
How is allergic rhinitis managed?
- allergen avoidance
- non sedating antihistamines eg cetirizine- nasally 1st then orally
- nasal saline washouts
- topical intra nasal steroids
- then refer to allergy clinic
- surgical reduction of inferior turbinates or correction of deviated nasal septum can help
When does a child receive vaccinations?
2,3,4 and 12 months, 2 years, 3.3 years, age 12/13 and 14
What can vaccines be made from? give an example for each (4)
- inactivated organisms (pertussis, poliomyelitis)
- live attenuated organisms (meales, mumps, rubella, BCG, OPV)
- secreted products (tetanus, diptheria)
- recombinant products
- constituents of cells wall (HiB, pneumococcus, meningococcus)
What is the difference in effect between plain polysaccharide vaccines (HiB, meningococcus, pneumococcus) and protein vaccines (tetanus, diptheria)
polysaccharides stimulate the immune system less broadly, so last less long.
Describe the clinical features of diptheria infection?
- Local disease: Affects URT with (pseudo-) membranous pharyngitis, enlarged anterior cervical nodes (BULL NECK) and soft tissue swelling
- Systemic disease: Toxin affects myocardium, nervous and adrenal tissues causes paralysis and cardiac failure
Describe the clinical features of pertussis infection (3 phases)
Clinical features: Initial catarrhal phase, similar to viral URTI.
Then paroxysms of intense coughing followed by ‘whoop’ or by vomiting. Infants may not have whoop rather periods of apnoea- can last months (called 100 day cough). Then chronic cough phase lasting for a few weeks.
Complications:
• Pneumonia
• Weight loss from repeated vomiting
• Cerebral hypoxia with resultant brain damage
• Severe and potentially fatal in infants under 6 months old
Describe the clinical features of a tetanus infection
Trismus (lockjaw) and facial spasms (risus sardonicus) Neck stiffness and difficulty swallowing, Spasms leading to opisthotinos, Pyrexia, sweating, elevated BP and tachycardia
What causes tetanus
Tetanus toxin, released following infection by the bacterium Clostridium tetani.
Tetanus spores are present in soil or manure and enter the body through a puncture wound, burn or scratch – which may go unnoticed.
Neonatal tetanus is due to infection of the umbilical stump
What causes polio
- poliomyelitis infection
- spreads faecal- oral
- virus multiplies in GI mucosa then drains to cervical and mesenteric lymph nodes then to blood stream
- in 5% it crosses blood brain barrier to enter CNS
How does polio present? 3 ways)
• Sub-clinical: 95% of cases experience no or mild coryzal symptoms.
• Non-paralytic: A small number will have flu-like symptoms such as a high fever, sore throat, headache, nausea and abdominal pain and aching muscles.
- Paralytic: Symptoms follow those of non-paralytic polio floppy muscle weakness. paralysis is irreversible and 5-10% will die from resp failure.
How may haemophilus influenza present?
Meningitis (commonest presentation), epiglottitis, bacteraemia without concomitant infection, pneumonia, pericarditis, septic arthritis, osteomyelitis, and cellulitis
Which meningitis vaccines are given and when are they given?
Hib/ MenC conjugate given at 12 months. MenACYW and 4CMenB at 14 yrs
When is MMR given?
12 months and booster at 3 yrs 4 months
What disease causes cough coryza and conjunctivitis, kolpik spots and maculopapular rash starting on face then behind ears, trunk and then extremities.
measles
give 3 complications of measles
- pneumonia, crough, otitis media
- diarrhoea
- encephalitis
State 3 types of non IgE mediated food allergy
- Food protein induced enterocolitis syndrome (FPIES)
- Food protein induced enteropathy (FPE)
- Coeliac
- Allergic proctocolitis (AP)
- dermatitis herpetiformis
State 3 types of IgE mediated food allergy
- anaphylaxis
- immediate gastrointestinal hypersensitivity
- pollen associated food allergy syndrome
- delayed food induced anaphylaxis to meats
- food induced exercise induced anaphylaxxis
