-
Type I: anaphylactic hypersensitivity
-
Type II: Cytotoxic hypersensitivity
- Rh disease
- Thrombocytopenia
-
Type 1 IgE mediated hypersensitivity
- Type I: anaphylactic hypersensitivity
- All the characteristics of a humoral immune response
- Allergen enters body and the body responds as if the allergen is a dangerous antigen or pathogen
- The allergen is taken up by antigen-presenting cells
- B cells are stimulated to mature into plasma cells which produce IgE
- IgE binds to mast cells and basophils
- Second time you are exposed, IgE is already bound to mast cells.
- Histamine is released
-
Allergen
A substance which triggers an allergic reaction in the body
-
Mast cells
- Are connective tissue cells found in the respiratory and gastrointestinal tracts and near blood vessels
- Filled with 500-1500 granules containing histamine and other physiologically active substances
- The difference between mast cells and basophils is mast cells are found outside of the CV system
-
Basophils
Circulating leukocytes in the blood that are also rich in granules
-
Histamine
- The most important mediator of allergic reactions
- A deriviative of the amino acid histidine
- Once in the bloodstream, histamine circulates to the body cells and attaches to the histamine receptors present on most body cells
- Constricts smooth muscles cells
-
Systemic anaphylaxis
- Most Dangerous Form of a Type I Hypersensitivity
- Allergens in the bloodstream can trigger mast cell degranulation that contracts smooth muscle
- Small veins constrict and capillary pores expand, forcing fluid into the tissues
- A drop in blood pressure, edema, and rash occur
- Contractions in the gastrointestinal tract and bronchial muscles cause cramps and shortness of breath
- The lungs fill with carbon dioxide
- This can cause death by asphyxiation in 10-15 minutes
-
Atopic Disorders
Are the Most Common Form of a Type I Hypersensitivity
-
Atopic disease is a
- Common (seasonal) allergy caused by the inhalation of pollen
- Year-round allergies can result from chronic exposure to allergens
-
Food allergies can cause symptoms like:
- swollen lips
- abdominal cramps
- nausea
- diarrhea
- hives
- anaphylaxis
-
Physical factors that can cause allergies include:
- extreme temperatures
- sunlight
- sweating
-
Exercise can cause allergies in the form of
An asthma attack
-
Allergic Reactions Also Are Responsible for Triggering
Many Cases of Asthma
-
Asthma can be caused by
airborne allergens, exercise, or cold temperature
-
Degranulation of mast cells releases
- mediators in the lower respiratory tract, causing:
- brochoconstriction
- vasodilation
- mucus buildup
-
Recruitment of eosinophils and neutrophils into the lower respiratory tract can cause:
- tissue injury
- airway blockage
-
Uticaria
Hives with red zones
-
Why Do Only Some People Have IgE-Mediated Hypersensitivities?
- Atopic people may lack sufficient IgA-secreting lymphocytes to block antigen stimulation in IgE
- Atopic people may have defective suppressor T cells, allowing for more IgE production
-
Allergies may help expel pathogens through:
- sneezing
- gastrointestinal tract contractions
-
Therapies Sometimes Can Control
Type I Hypersensitivities
-
Desensitization therapy involves a series of injections of allergens which may
- Cause gradual reduction of granules in sensitized mast cells
- Cause production of IgG antibodies that neutralize allergens (blocking antibodies)
-
Treatments
- Monoclonal antibodies
- Antihistamines
- Corticosteroids
-
Monoclonal antibodies can be used to
- Dislodge IgE from mast cells and basophils
- This prevents allergic reactions
-
Antihistamines block
The effect of histamine
-
Corticosteroids are
- Inhaled through the nose to relieve symptoms
- Some also block mediator release
-
Type II Cytotoxic Hypersensitivity
- A cell damaging, humoral immune response occurring when IgG reacts with antigens on the surfaces of cells
- It occurs when IgG reacts with antigens, often activating complement
-
Hemolytic disease
- Type II. Rh disease
- When an Rh+ man and an Rh- woman produce an Rh+ child, the mom can produce antibodies against the newborns blood when placenta rips.
- When the second child is born, mom already has antibodies and they destroy some of the fetus�s red blood cells leading to anemia and hemolytic disease.
-
-
Wheal
Rash consisting of central puffiness
-
Thrombocytopenia
- Platelets are destroyed
- Aspirin, antibiotics, and antihistamines can bind to platelets. Body reacts to the foreign substance and sends in the IgG
-
Type III: immune complex hypersensitivity
- Serum sickness (arthus reaction)
- Rheumatoid arthritis
-
Immune hypersensitivity 1-3 can occur
In a matter of minutes
-
Type IV: cellular hypersensitivity
Cell mediated reaction takes 24-72 hours
-
Induration
Thickening and drawing of the skin
-
-
Infection allergy
Like the TB test
-
Contact dermatitis
Poison ivy
|
|
