Lecture 1- Hypersensitivity 1 Flashcards Preview

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1

The immune system is responsible for protection against

Infection and noninfectious agents

2

Failure of the immune system can lead to disease such as

immunodeficiency disease, auto immune disease and allergy.

3

Over activation of the immune system caused by

  • infectious agents
  • environmental substances
  • or self antigen can lead to disease driven by hypersensitivity reactions

4

  • Immunodeficiency is

  • either primary (genetics) or secondary (HIV)
  • Malnutrition is the major cause of immunodeficient

5

examples of harmful effects of the immune system

either:

  • Organ specific diseases (tissue/cell damage)
  • Change in function of organs (physiological change)

6

hypersensivity is defined as 

“the antigen-specific immune responses that are either inappropriate or excessive and result in harm to host”

  • ANTIGEN MEDIATED
  • mechanisms underlying these aberrant immune responses are those employed by the host to fight infections

7

Hypersensitivity can be divided into 4 categories, each with a different mechanism for disease development.

Types of hypersensitivity reaction

1. Type I – Immediate - Allergy- ~5mins

2. Type II- Antibody mediated -5-12h

3. Type III- Immune complex mediated – 3-8h

4. Type IV- Cell medicated- Delayed 24-72h

8

  • Hypersensitivity to exogenous antigens

  • Non infectious substances (innocuous) e.g. allergies such as pollen, house mite, peanut etc
  • Infectious microbes
    • Esp gram negative can drive abnormal response e.g. sepsis
  • Drugs (penicillin)

9

Hypersensitivity to intrinsic antigens

 

 

  • Infectious microbes (mimicry)
    • Microbe associates with self antigen and therefore body recognises self as foreign
    • E.g. strep throat leading to endocarditis
  • Self antigens (auto-immunity)
    • Persistent reaction because of persistence of antigen

10

Type I,II and III are all

antibody mediated

11

ttpe IV is 

cell mediated

12

Type 1 hypersensitivity 

  • Type I or immediate (Allergy)
    • Environmental non- infectious antigens
    • IgE

13

Type II hypersensitivity reaction

  • Type II or antiBody mediated
    • IgG, IgM (insoluble antigen e.g. membrane bound)

14

type III hypersensitivity reactions

  • Type III or immune Complexes mediated
    • IgG, IgM (soluble- binds to antigen in the blood stream- forming complex)

15

Type IV hypersensitivity reaction

  • Type IV or cell mediated (Delayed)
    • Environmental infectious agents and self-antigens

16

difference between Type I, II and III

I- IgE 

II - IgG, IgM (insoluble antigen e.g. membrane bound)

III - IgG, IgM (soluble- bind to antigen in the blood stream forming complex)

17

Common features of hypersensitivity reactions

 

 

  • Sensitization phase
  • Effector phase

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Sensitization phase

First encounter with the antigen. Activation of APCs and memory effector cells. A previously exposed individual to the antigen is said to be “sensitized”

19

Effector phase

Pathologic reaction upon re-exposure to the same antigen and activation of the memory cells of the adaptive immunity

Will only have hypersensitive reaction outcome in effector phase

20

hypersensitivity type I also known as

allergy

21

outline Type I reaction (allergy)

Development of allergy specific antibodies resulting in mast cell degranulation.

22

Treatment for type I hypersensitivity reactions include:

• Allergen desensitisation

• Anti IgE antibody

• Antitistamine

• Leukotriene receptor antagonists

• Corticosteroids

23

outline Type 2 reaction

  • Usually develops within 5-12 hr
  • Involves IgG or IgM antibodies
  • Targets cell bound antigens
    • Exogenous: Blood group antigens, Rhesus D antigens
    • Endogenous: self-antigens
  • Induces different outcomes
    • Tissue/cell damage
    • Physiological change

Antibody binds with cell surface antigen to activate compliment resulting in cell and organ damage.

24

Examples of hypersensitivity type II reactions include:

• Haemolytic transfusion reactions

• Haemolytic disease of the newborn

• Myasthenia gravis

• Graves’ disease

• Autoimmune haemolytic anaemia (warm and cold)

• Immune thrombocytopenia Purpura

• Goodpasture’s syndrome

25

Mechanisms of tissue damage and physiological change caused by type II hypersensitivity reactions

26

Importance of the complement pathways

Deficiency in complement can lead to hypersensitivity

27

Type II Treatment options

Cell tissue damage

• Anti-inflammatory drugs e.g. oral prednisolone

• Plasmapheresis

• Splenectomy

• Intravenous immunoglobulin (IVIG)

Physiological change

• Correct metabolism

• Replacement therapy

28

An example of disease caused by type II hypersensitivity (IgM)

 

  • Haemolytic transfusion reaction

29

Immune mechanism of haemolytic transfusion reaction

 

  • Incompatibility in the ABO or rhesus D antigens
  • Donor RBC destroyed by recipient’s immune system
  • RBC lysis induced by type II hypersensitivity involving by the naturally occurring antibodies (IgM)

30

 

An example of disease caused by type II hypersensitivity (IgG)

 

Haemolytic disease of newborn