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.

Portuguese man-of-war

Portier and Richet :

Anaphylaxis 過敏反應 ↕Prophylaxis 預防

Richet was awarded the Nobel Prize in 1913 for the discovery of anaphylaxis.

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 IIIHypersensitivity

tissue damage

Localized Type III Reaction - Arthus Reaction

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