Section 2 Hypersensitivity Reactions. 1.Type I hypersensitivity (Anaphylactic type) Immediate hypersensitivity reaction, resulting from release of pharmacologically.

Section 2 Section 2 Hypersensitivity Hypersensitivity

ReactionsReactions

1.1. Type I hypersensitivity Type I hypersensitivity (Anaphylactic type)(Anaphylactic type)

Immediate hypersensitivity reaction, resulting from release of pharmacologically active mediators.

Slide 7.9

Activation of mast cells in type I hypersensitivity and release of their mediators. ECF, eosinophil chemotactic factor; NCF, neutrophil chemotactic factor; PAF, platelet-activating factor. (From Robbins Basic Pathology ,2003 ）

(2) (2) Tissue reactions: variable in severityTissue reactions: variable in severity

Mildest may be only edema. Reaction is triggered by mast cells, basophils. If inflammatory cells are present, many are eosinophils.

(3) Diseases

① Urticaria and angioneurotic edema

② Asthma

③ Hay fever

④Insect allergy: serious or fatal anaphylaxis may follow. Edema of larynx, with airway obstruction may occur.

2. Type II Hypersensitivity

Cytolytic or cytotoxic reactions

(1) Mechanism:(1) Mechanism: ① Complement-dependent reactions

Transfusion reactionsErythroblastosis fetal Autoimmune hemolytic anemiaCertain drug reactions

②Antibody-dependent cell-mediated cytotoxicit

(ADCC).

May be relevant to:

Graft rejection

The destruction of targets too large to be

phagocytosed, such as parasites or tumor cells.

③Antibody-mediated cellular dysfunction

Myasthenia gravis: muscle weakness

Graves’ disease:Graves’ disease: hyperthyroidism

Slide 7.10

Schematic illustration of three different mechanisms of antibody-mediated injury in type hypersensitivity. A, Complement-dependent reactions that Ⅱlead to lysis of cells or render them susceptible to phagocytosis.

(From Robbins Basic Pathology ,2003 ）

Slide 7.11

Antibody-dependent cell-mediated cytotoxicity (ADCC). IgG-coated target cells are killed by cells that bear Fc receptors for IgG (e.g., NK cells,

macrophages). . (From Robbins Basic Pathology ,2003 ）

Slide 7.12

Antireceptor antibodies disturb the normal function of receptors. In this example, acetylcholine receptor antibodies impair neuromuscular transmission

in myasthenia gravis. (From Robbins Basic Pathology ,2003 ）

3. 3. Type Hypersensitivity ⅢType Hypersensitivity Ⅲ(Immune complex-mediated)(Immune complex-mediated)

(1) Reaction types(1) Reaction types

① Arthus reaction

② serum sickness

③ Collagen diseases

(2) (2) Toxic complex diseases:Toxic complex diseases:

① Acute glomerulonephritis

② Systemic lupus erythematosus

③ Necrotizing angiitides

④ Rheumatoid arthritis

⑤ Progressive systemic sclerosis

⑥ Dermatomyositis etc.

Slide 7.13

Schematic illustration of the three sequential phases in the induction of systemic type (immune complex) hypersensitivity. Ⅲ(From Robbins Basic Pathology ,2003 ）

Slide 7.14

Schematic representation of the pathogenesis of immune complex-mediated tissue injury. The morphologic consequences are depicted as boxed areas. . (From Robbins Basic Pathology ,2003 ）

Slide 7.15

Immune complex vasculitis. The necrotic vessel wall is replaced by smudgy, pink “fibrinoid” (Dr. Trace Worrell)

(From Robbins Basic Pathology ,2003 ）

4. Type HypersensitivityⅣ

(Cell-Mediated )

Delayed hypersensitivity reaction

(1) TissueTissue reactionreaction: Consist of parenchymal destruction associated with perivascular lymphocytic and macrophage reaction.

(2) (2) Diseases:Diseases:

① ① Chronic active hepatitisChronic active hepatitis

② ② Viral exanthem(Viral exanthem( 皮疹）皮疹） ③ ③ Contact dermatitisContact dermatitis

④ ④ Graft rejectionGraft rejection

⑤ ⑤ Inflammatory bowel disease. Inflammatory bowel disease.

Slide 7.16

Delayed hypersensitivity in the skin. Immunoperoxidase staining reveals a predominantly perivascular cellular infiltrate that marks positively with anti-CD4 antibodies. ( Dr. Louis Picker) .

(From Robbins Basic Pathology ,2003 ）

Slide 7.17

A section of a lymph node shows several granulomas, each made up of an aggregate of epithelioid cells and surrounded by lymphocytes. The granuloma in the center shows several multinucleate giant cells. ( Dr. Trace Worrell) (From Robbins Basic Pathology ,2003 ）

Slide 7.18

Schematic illustration of the events that give rise to the formation of granuloma in type Ⅳhypersensitivity reactions. Note the role played by T cell-derived cytokines. . (From Robbins Basic Pathology ,2003 ）