Allergy

Allergy

Inapproprite reaction of the immune system to a substance (allergen) and one of four hypersensitivity reactions of the immune system

hypersensitivity

undesirable immune reactions produced by the normal immune system and requires a pre-sensitised state of the host

Type I hypersensitivity

allergic reactions

• development of symptons following exposure to an allergen and can be IgE or non-IgE mediated

• can range from mild to sever with anaphylaxis being the most severe

symptoms of allergy (skin and mucous membranes)

• atopic dermatitis (eczema)

• urticaria (hives)

• angiodema (swelling of tissue)

• contact dermatitis

• oral symptoms (swelling and irritation of tissue in and around mouth)

• oral allergy syndrome

Symptoms of allergy (digestive tract)

• diarrhea

• constipation

• nausea and vomiting

• abdominal bloating and distension

• indigestion

• belching

symptoms of respitary tract

• seasonal or perennial rhinitis (hayfever)

• Rhinorrhea (runny nose)

• allergic conjunctivitis

• serous otitis media (earache with effusion)

• laryngeal oedema

• asthma

symptoms of nervous system

• migraines and headaches

• spots before the eyes

• listlessness

• hyperactivitiy

• lack of concentration

• tension fatigue syndrome

• irritability

• chills

• dizziness

anaphylaxis

severe reaction of rapid onset, involving multiple organ systems that results in circulatory collaspe and drop in blood pressure.

development of allergy

• first exposure to allergen

• extraction of antigen

• activation of antigen-specific T cells

• production of IgE and bind to mast cells

immunology of allergic response

• B cell comes into contacts with allergen exposed T and differentiates into antibody secreting plasma cell

• IgE antibodies produced will bind to surface of mast cells

• when exposed to allergen again, IgE antibodies on mast cell become cross linked with antigen

• mast cell will degranulate and release histamine and other chemicals

early phase allergic response (minutes)

• classic allergic reaction

• flushing

• hypotension

• increased mucus production

• pruritus

• smooth muscle contraction

• vascular leakage

delayed (hours)

• late-phase reaction

• oesinophil infiltration

• neutrophil infiltration

• fibrin deposition

• mononuclear infiltration

• tissue destruction

IgE mediated reactions

• immediate (<1 hour)

• anaphylaxis, hypotension, laryngeal edema, urticaria/angiodema, wheezing

• accelerated (1-72 hours)

• urticaria, angiodema, laryngeal edema, wheezing

non- IgE mediated reactions

• late (>72 hours)

• rash, serum sickness, cytopenias or haemolytic anaemia, drug fever, hypersensitivity

allergic rhinitis

• inflammation of the nasal mucosa due to hypersentivity to environmental allergens

• mediated by degranulation of mast cells and eosinophils

• effects felt within minutes

allergic rhinitis mechanisms

• APC present allergen to Th2 T cell which release IL-4

• IL-4 acts on B cells which produces IgE that sticks to mast cell surface

• IgE induces degranulation

immediate phase reaction of rhinitis

• histamine, leukotrienes and prostaglandins induce immediate symptoms (minutes)

• smooth muscle contraction

• sneezing

• nasal discharge

late phase reaction of rhinitis

• release of cytokines, chemokines and enzymes induce late stage reactions that act on eosinophils that cause them to degranulate. (hours)

• edema

• induration broncoconstriction

asthma

• chronic inflammation disorder of the airways

• inflammation causes recurrent episodes of wheexing, chest tightness, breathlessness and cough at night or early morning

• increase in airway responsiveness to variety of stimuli

airway inflammation

• early even in asthma that is primarily allergen mediated with some environmental factors

compoonents of airway inflammation

• infiltration of cells (eosinophils and CD4+ lymphocytes)

• change in resident cells (mainly Th2 T cells secreting IL4 etc)

• changes in non-cellular components of airway wall

pathogenesis of asthma

• chronic mucus plug formation

• airway remodeling — irreversible

chronic mucus plug formation

persistent airflow limitation in severe intractable asthma

airway remodelling

irreversible component of airflow limitation due to structural airway matrix changes

common food allergies

• eggs

• cow’s milk

• soy

• fish

• wheat

• nuts

mild-moderate food allergy symptoms

• swelling of face, lips and/eyes

• skin hives

• abdominal pain

• vomiting

severe symptomes of food allergy

• difficulty breathing

• tongue swelling

• throat swelling or tightnes

• wheeze

• persistent dizziness or collaspe

• pale and floppy (young children)

Laboratory diagnosis of food allergy (IgE mediated)

• skin prick test (cutaneous test)

• blood tests (not common)

cutaneous test

• routine diagnosis in atopic/anaphylactic disease

• drop of concentrated aqueous allergen extract is placed on the skin

• then skin is pricked lightly with a needle

• after 20 minutes, the reaction is graded and recorded

blood tests

• IgE may be elevated in patients but does not necessarily correlate to clinical symptoms

• tryptase level maybe elaveted — indication of mast cell degranulation

• elevated eosinophil count

• RAST/CAP or RAST/ImmunoCAP measures antigen specific IgE

prevention of food allergy

• avoiding triggers that cause allergic reaction

• medical ID tag can be worn by people with anapylaxis

• carrying Epipen for people with history of serious allergic reaction