Download Type I Hypersensitivity

Chapter 15
Hypersensitivity Reactions
Mast cell
Although the word “hypersensitivity”
implies an increased response, the immune
response of a hypersensitivity reaction is
not necessarily heightened but instead, an
inappropriate response to an antigen.
Portier and Richet :
Anaphylaxis 過敏反應
↕
Prophylaxis 預防
Richet was awarded the
Nobel Prize in 1913 for the
discovery of anaphylaxis.
Portuguese man-of-war
Four Types of Hypersensitive Responses
Immediate Hypersensitivity:
Type I
IgE-mediated hypersensitivity
Type II
IgG- or IgM-mediated cytotoxic
hypersensitivity
Type III Immune complex-mediated hypersensitivity
Delayed-type Hypersensitivity:
Type IV Cell-mediated hypersensitivity
Type I Hypersensitivity
- IgE-mediated hypersensitivity
allergen (過敏原), allergic (過敏的)
atopy (過敏體質), atopic (具有過敏體質的)
Transfusion
Reactions are
Type II
Reactions
Hemolytic Disease of the New Born is Caused by Type II Reactions
Type III
Hypersensitivity
Localized Type III Reaction
- Arthus Reaction
tissue damage
Generalized Type III Reaction – Serum Sickness
fever, weakness, rashes,
edema, erythema, arthritis,
glomerulonephritis
Type IV Hypersensitivity
Some populations of activated TH cells encounter certain
types of antigens, they secrete cytokines that induce a localized
inflammatory reaction called delayed-type hypersensitivity
(DTH).
The term “hypersensitivity” is misleading, since it suggests
that a DTH response is detrimental.
Although a DTH response can cause extensive tissue damage
in some cases, DTH plays an important role in defense against
intracellular pathogens .
Granuloma Formation
- Caused by a prolonged DTH response
Contact Dermatitis
Is A Type of DTH
formaldehype, trinitrophenol,
nickel, turpentine, detergents,
poison ivy, poison oak, and
active agents in various
cosmetics and hair dyes
Summary