allergy Flashcards
how many types of hypersensitivity reactions are there?
there are 4 types of hypersensitivity reactions. they are broadly classified based on cells and immune effectors that are involved
what type of hypersensitivity reaction is an allergic response?
an allergic response is a type 1 hypersensitivity reaction - as it was discovered first
what is an atopic allergy?
in Greek means out of place work.. it is an inappropriate reaction that is out of place
what are the two key players in atopic allergy’s?
1- mast cell( part of anatamine system abd found in mucosal tissues, gut, skin )
2- IGE-( particular antibody/ antiglobulin)
what happens when mast cells are released and dispersed within an extracellular environment?
mast cells undergo degranulation
are mast cells antigen specific?
no they are not antigen specific, they are part of the innate immune system. they have a FC receptor which it binds to. this allows it to target
what antibody is dominant in an allergic reaction?
IGE
when is IGE produced?
IGE is inappropriately produced in response to innocuous allergens that can medicate allergic reactions
are total IGE levels predictive of atopic disease?
no
what is an allergen?
an allergen is what drives an allergic response. they tend to be protein-based. they are low molecular weight, highly soluble and stable
why do we have allergens?
they are due to an inappropriate breakdown of tolerance
what is sensitisation?
it is the initial exposure to antigen leading to antibody IGE production
what happens in sensitization and where does it take place?
it is the differentiation of native T cells in the th2 phenotype cells. it takes place in lymph nodes. dendric cells have matured and carried allergens to lymph nodes. during expansion the cutokine environment switches to the th2 phenotype. and one of the key cytokines that mediate is IN4. this causes skweing
what is sensitization linked to?
it is thought to be linked to the allergen dose / intrinsic properties of allergen and the route of exposure.
what does sensitisation stimulation B cells do?
produce cytokines of immune response which provide more IL4 to initiate a class switch to producing IGE.
what is the consequence of an allergen response?
allergen passes through mucosa and is captured.
it is transported to lymph cells- prime to th2 phenotype.
skewes b cells to IGE phenotype- they then differenciate into plasma cells
these antibodies travel through body back onto the mucosa on mast cells using FC receotirs.
so if encountered again this causes corss linking- degranulation and signalling
what happens in an acute/ immediate response?
occurs in a range of tissues- vasoactive amines within the cell cause:
smooth muscle constriction
blood vessel constriction
increase in mucous production
never endings -pain and distress
and recruitment of other cells such as eonysophyls
what happens in the scamatic?
Mast cellls binds to IGE receptors
these allergies lead to a signal in these cells.
consequence depends on allergen present
what are the responses seen in an allergic response?
GI- diarrhoea/ peristalysis
eye/ nasal- wheeze or cough
blood- risk of anaphlactic shock- critical drop in BP and decreased in permeability
what happens in the early stage of an allergic reaction?
physiological mechanism
kiss of organ function due to- mucous production/ vasodilation and swelling/ bronchoconstriction
what happens in late stage of an allergic reaction?
we get WBC flodding into environment/ scarring
immunological mechanisms/ digestion of tissue smooth muscle.
what are contained in mast cells and what are they used for?
histamine
leukotrines- effects vascular permeability
neutrophils and eosinophil attracting chemokines- this leads to WBC into tissue inflamatory cascade
what are present in eosiniphils?
typcially found in the blood
recruited by macrunophil degranulation
conatin matalloproteinases an d collagenases- digestion of tissue
fibrotic cytokines- secrete due to fibrosis and scarring
t and b cells attracting chemokines- worsen effects
what is seen in a lung and skin graph to show function?
both have an initial drop in function but later on a broader dip that lasts longer
is allergic reaction a vigerous circle?
yes
how much of the uk have an alergy?
1/3
how much is spent each year on allergy medication?
aprox 1 billion
what is an atopic disease?
often present with food allergies in children but can disappear overtime
what allergy may develop at adulthood?
asthma
are all allergic reactions presentation the same?
no but the response is
IV allergens can result in what?
anaphylactic shock
what is the pathway for an allergic reaction?
allergen to IGE> Granulation> amine and physiological reaction
describe athsma reaction?
- Chronic disorder of airways with variable airlow limitation
- Recurrent epsoides of wheeze, breathlessness, chest tightness and cough( particularly at night)
- Inhaled allergens most common ( although can be triggered by food and drugs)
describe rhinitis
- Most prevalent respiratory disease
- Nasal itching, blockage, rhinorrea, anosmia( loss of smell and sense of taste) and frequent sneezing
- Often linked with asthma and vice versa
describe uricicaria and angiodema
URTICARIA- upper latyers of skin AND ANTGIODEMA- deeper layers of dermis
- Raised itchy nettle rash also known as hives
- Usually triggered by food and drug allergens
describe eczema
- Local erythematous inflammation of the skin
- Often appears In early childhood induced by food such as eggs and milk
describe anaphylaxis
- Most severe allergic reaction
- Involves more than one body system- respiratory/ blood/ cardiovascular/ gi
- Life threatening and can result in death without AD- epipinephrine( epipin)
- Triggered by many allergens including foods/ deugs/ venoms and latex
is there a link between genetics and allergies?
yes strong link
what is the hygiene hypothesis?
- developed world less causes
-elstest child more likely to develop
c-section- more likely to develop allergy
how do you diagnose an allergy?
clinical history
skin prick test
challenge test
what is a skin prick test?
allergen apploed to skin. reaction if granulation and swelling.
what is a challenge test?
- Can provoke an immune response by oral/ inhaled/ injected or skin contact to suspected allergens
