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Type 1: Allergic reaction, Mediated by IgE,
Inflammation due to mast cell degranulation
Local symptoms:
-itching
-rash
Hypersensitivity: Type 1
Systemic symptoms:
-wheezing
Most dangerous = anaphylactic reaction
systemic response of hypotension, severe
bronchoconstriction
Main treatment: epinephrine reverses the effects
, Type 2: Cytotoxic reaction; tissue specific (ex: thyroid
tissue)
Macrophages are the primary effectors cells involved
Can cause tissue damage or alter function
Hypersensitivity: Type 2 Grave's disease (hyperthyroidism) - example of
altering thyroid function, but does not destroy thyroid
tissue
Incompatible blood type- example of cell/tissue
damage that occurs; severe transfusion reaction
occurs and the transfused erythrocytes are destroyed
by agglutination or complement-mediated lysis.
Type 1 Hypersensitivity
Organ Specific
Antibody binds to the antigen on the cell surface
Type 1 Hypersensitivity VS. Type 2 Hypersensitivity
Type 2 Hypersensitivity Not Organ Specific
Antibody binds to the soluble antigen outside the cell
surface that was released into the blood or body
fluids, and the complex is then deposited in the
tissues
Rheumatoid arthritis: Antigen/antibodies are
deposited in the joints
Hypersensitivity: Type 3 -
Examples Systemic Lupus Erythematosus (SLE)- very closely
related to autoimmunity- antigen/antibodies deposit
in organs that cause tissue damage
, Delayed response
Does not involve antigen/antibody complexes like
Hypersensitivity: Type 4
Types 1, 2 and 3
Is T-cell mediated
Type 1: Immediate hypersensitivity reactions, termed
atopic dermatitis, are usually characterized by widely
distributed lesions
Type 4: Contact dermatitis (delayed hypersensitivity)
Differentiating Between
consists of lesions only at the site of contact with the
the Rash of a Type 1 vs.
allergen
Type 4 Reaction:
The key determinant is the timing of the rash:
-Type 1 = Immediate
-Type 4 = Delayed: Several days following contact, ex
would be poison ivy
A non-severe case of contact dermatitis would be
treated with topical corticosteroid.
Why not epinephrine or antihistamines?
Treatment of Type 4 Rash -Epinephrine is for emergent Type 1 anaphylactic
reactions. Antihistamines act on the H1 receptors.
Type 4 does not involve mast cells and H1 receptors.
Antibiotics not appropriate since not an infection