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
