Immediate Hypersensitivity (Hypersensitivity type 1)
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Transcript Immediate Hypersensitivity (Hypersensitivity type 1)
Allergy
Chapter 20
Immediate hypersensitivity because it begins rapidly, within minutes of antigen challenge
(immediate), and has major pathologic consequences (hypersensitivity)
In clinical medicine, these reactions are called allergy or atopy, and the associated
diseases are called allergic, atopic, or immediate hypersensitivity diseases
A variety of human diseases are caused by immune responses to nonmicrobial
environmental antigens that involve TH2 cells, immunoglobulin E (IgE), mast cells,
and eosinophils
Allergy is the most common disorder of immunity and affects 20% of all individuals
in the United States
General Features of Immediate Hypersensitivity Reaction
Hallmarks of allergic diseases are the activation of Th2 cells and the production of IgE
antibody
Strong genetic predisposition
Allergens, are usually common environmental proteins and chemicals
Cytokines produced byTh2 cells
Clinical and pathologic manifestations consist of the vascular and smooth muscle reaction
that develops rapidly after repeated exposure to the allergen (the immediate
reaction) and a delayed late-phase reaction consisting mainly of inflammation
Allergic reactions are manifested in different ways, depending on
the tissues affected, including skin rashes, sinus congestion,
bronchial constriction, abdominal pain, diarrhea, and systemic
shock (Anaphylaxis)
PRODUCTION OF IGE
IgE antibody is responsible for sensitizing mast cells and provides recognition of antigen
for immediate hypersensitivity reactions
Atopic individuals produce high levels of IgE in response to environmental allergens,
whereas normal individuals generally synthesize other Ig isotypes, such as IgM and IgG,
and only small amounts of lgE
The Nature of Allergens
Antigens that elicit immediate hypersensitivity reactions (allergens) are proteins or
chemicals bound to proteins to which the atopic individual is chronically exposed
Typical allergens include proteins in pollen, house dust mites, animal dander, foods, and
chemicals like the antibiotic penicillin
Two important characteristics of allergens are that individuals are exposed to
them repeatedly and, unlike microbes, they do not generally stimulate the innate
immune responses that are associated with macrophage and dendritic cell secretion of
TH1- and TH17-inducing cytokines
Chronic or repeated T cell activation in the absence of strong innate immunity
may drive CD4+ T cells toward the TH2 pathway, as the T cells themselves make
IL-4,
These features include low to medium molecular weight (5 to 70 kD), stability,
glycosylation, and high solubility in body fluids
Many allergens, such as the cysteine protease of the house dust mite
Dermatophagoides pteronyssinus and phospholipase A2 in bee venom, are enzymes,
but the importance of the enzymatic activity
Polysaccharides cannot elicit these reactions unless they become attached to proteins,
and penicillin react chemically with amino acid residues in self proteins to form haptencarrier conjugates
Specific IgE antibodies
Aero-allergens
Food allergens
Allergic Reaction
Skin Prick Test
(SPT)
THE PROTECTIVE ROLES OF IgE- AND MAST CELL–
MEDIATED IMMUNE REACTIONS
Immunotherapy for Allergic Diseases
Several empirical protocols have been developed to diminish specific IgE synthesis called
desensitization, small quantities of antigen are repeatedly administered subcutaneously
IgG titers often rise, perhaps further inhibiting IgE production by neutralizing the
antigen and by antibody feedback, and induction of Treg to iduce tolerance
Changing the predominant phenotype of antigen-specificT cells fromTH2 to TH1
Other approaches being used to reduce IgE levels include systemic administration of
humanized monoclonal anti-IgE antibodies mentioned earlier
Allergic Diseases
Allergic Rhinitis
Allergic Rhinitis :
AR is the most common form of perennial rhinitis ( % 43 – 77 )
AR is the most common form of allergy ( 500,000,000 )
Risk factors
1 - positive family history of AR
2 – high socio-economic class
3 – total IgE > 100 before 6 year
4 – passive smoking especially before 1 yr
5 – feeding start before 6 month
6 – heavy contact with indoor allergens (esp. mite)
7 – male gender ?
8 – birth in pollination season ?
9 – first baby ( single baby ) ?
AR classification
Allergic Rhinitis
&
seasonal
perennial
&
intermittent
persistent
AR classification
1 – seasonal allergic rhinitis ( SAR ) :
- often related with outdoor allergens
- tree pollens in early spring
- grass pollens in spring & summer
- weed pollens in summer & autumn
2 – perennial allergic rhinitis ( PAR ) :
- often related with indoor allergens
- mite , cockroach , danders , mold &…
Inflammatory cells in allergic rhinitis
1 – mast cell
2 – eosinophils
3 – T lymphocyte
4 – dendritic cells & macrophages
5 – epithelial cell
Clinical manifestations :
Classic symptoms of allergic rhinitis are :
1 – sneezing
2 – itching ( itchy nose )
3 – rhinorrhea ( runny nose )
4 – blockade ( congestion )
Treatment :
1 – Environment control :
aeroallergen & food allergen
irritants
2 – pharmacotherapy :
intermittent ----- anti-H +/- decongestant
persistent ------- INCS
3 – Immunotherapy
ASTHMA
Asthma is one of the most common chronic diseases, with an estimated 300
million individuals affected worldwide. Its prevalence is increasing,
especially among children
Asthma is a chronic inflammatory disorder of the airways
Asthma is not a cause for shame. Olympic athletes, famous leaders, other
celebrities, and ordinary people live successful lives with asthma
Prevalence data for childhood asthma
Male > female ( prepubertal )
Female > male ( postpubertal )
Urban > rural
Developed (western) > undeveloped countries
Slack > white ( minimal different )
School age > preschool age ( prevalence )
Preschool age > School age ( incidence )
Allergy & asthma ?
Childhood
asthma
Adult
asthma
% 80 allergic
% 50 allergic
Risk factors for asthma
atopy
allergy to house dust mite
allergen exposure
family history of asthma
early viral RTI
passive smoking
cigarette smoking
maternal smoking
prematurity
male gender
length of breast feeding
food intolerance & hypersensitivity
high dietary intake of sodium
air pollution
urban living
Hygiene – hypothesis
Pathogenesis
Clinical manifestation
The classic symptoms of asthma
cough
wheez
Chest
Thightness
chest
pain
Treatment
Atopic dermatitis (atopic eczema)
Age-specific lesions of AD
- in infants
cheek , scalp , extensors surface
- in older children & adult
flexors (politeal fossa, antecubital
fossa )
Environment factors
1 – allergens ( aeroallergen – food allergen )
2 – irritants ( detergent-soaps-low humidityhigh humidity-hot air-cold air-,… )
3 – infections ( S.A , HSV , malsseziafurfur )
4 – emotional stress
5 – endocrine factors
Vicious cycle of skin infection and AD
Decreased function
Of skin barrier
AD
Skin infections
Triggers of atopic dermatitis
Local
treatment
treatment
Systemic
treatment
Environment
control
Anaphylaxis
Etiology
Foods : 36%
Drug : 17%
Insect sting : 15%
others: 32%
( latex– exercise– cold- idiopathic)
The most common causes of
anaphylaxis
Foods
Peanut
Tree nut
Fish
Shellfish
Egg
Cows milk
wheat
Drugs
Antibiotics
Aspirin
NSAIDs
Anesthetic agents
Opioids
RCM
Clinical manifestation
Cutaneous : 80-90%
flushing, urticaria angioedema
Respiratory : 50-60%
hoarseness, nasal congestion, sneezing, dyspnea, cough, wheezing and laryngeal
edema
Cardiovascular : 30-35%
hypotension,dysrrhytmia, arrhythmia, myocardial ischemia
Gastrointestinal : 20-25%
nausea, abdominal cramping, vomiting, and diarrhea
Miscellaneous:
headache : 5-8%, Substernal pain :4-6%, Seizure :1-2%
Treatment
Epinephrine ( Adrenaline )
H1 blocker ( Diphenhydramine )
H2 blocker ( Ranitidine )
Corticosteroid ( Hydrocortisone )
B2 agonist ( Ventolin )
Urticaria / Angioedema
Episodes of hives that continue for < 6 week are considered acute, and
Those that persist for > 6 week are designated chronic
Etiology
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
Foods & food additives
Drugs
Insect bite & insect sting
Latex & other contactants
Physical agents
Infections
Transfusion reactions
CVD
Malignancy
Complement disorders
Hereditary disease ( HAE , muckle-well , … )
Systemic disease ( PV , systemic mastocytosis ,.. )
Idiopathic
Acute urticaria
IgE - mediated
Foods , drugs , insect sting , latex , …
Directly: morphine, exercise, cold, sunlight
Non-IgE-mediated
Leukotrienes change: aspirin & NSAIDS
Alternative pathway activation: RCM
Acute urticaria
Cold urticaria
Dermatographism
Solar Urticaria
Chronic urticaria
Chronic urticaria is reported to be more common in adults, while acute urticaria is more
common in children
Both sexes are affected; however, chronic urticaria is more common in women,
especially in middle-aged women
CIU occurs twice as often in women as in men
Urticaria
Male = female
Acute
urticaria
More common in children and adolescent
peak : 20 – 30 year
Often due to foods & drugs
% 15 – 20 of GP
female > male
chronic
urticaria
More common in middle age
peak : 30 – 50 year
Often idiopathic ( CIU )
Approximately % 1
Etiology of Chronic urticaria
% 80
Idiopathic ( CIU )
% 15
Physical agents
%5
Autoimmunity , malignancy , complement
disorder , occult infections , systemic disease ,
…
Antihistamines & urticaria
Classification of angioedema without urticaria
ACE - inhibitor angioedema
HAE ( treatment )
Treatment of HAE is difficult
For acute attacks, C1 INH concentrate or FFP should be administered
Intubation or tracheotomy may be necessary
Corticosteroids and antihistamines are not helpful
Subcutaneous adrenaline ( 0.01 ml / kg , epinephrine 1 : 1000,
max = 0.3 ml ) may be tried