Hypersensitivity reaction

1. Dr. Sara
Sadiq

2. Hypersensitivity
 Exaggerated or
Inappropriate immune
response that is harmful to
the host

3. Atopy:
 Atopy is the term for the genetic trait to have a
predisposition for localized anaphylaxis
 Atopic individuals have higher levels of IgE and
Eosinophills

4. Allergens
• Allergens are nonparasite antigens that can
stimulate a type I hypersensitivity response.
• Allergens bind to IgE and trigger degranulation of
chemical mediators.

5. Hypersensitivity Reactions
 Immediate hypersensitivity refers to
antibody mediated reactions – symptoms
develop within minutes to hours
 Delayed hypersensitivity refers to cell
mediated immunity, symptoms not observed for
24 to 48 hours.

6. Four Classifications
 Type I (Immediate) Hypersensitivity
 Type II (cytotoxic) hypersensitivity
 Type III (immune complex mediated)
hypersensitivity
 Type IV (delayed) hypersensitivity

8. Type I Hypersensitivity
(Anaphylactic) Reactions/Allergy
 Occur within minutes of exposure to
antigen
 Antigens combine with IgE antibodies
 IgE binds to mast cells and basophils,
causing them to undergo degranulation
and release several mediators:
 Histamine
 Prostaglandins
 Leukotrienes
 Anaphylactic shock

9. Type I (Immediate) Hypersensitivity

10. Mast Cells and the Allergic Response

11. Mast Cells and the Allergic Response

12. Type I (Immediate) Hypersensitivity

13. Examples of type 1
 Allergic asthma
 Allergic conjunctivitis
 Allergic rhinitis
 Anaphylaxis
 Angioedema
 Urticaria (Hives)

14. Type II Hypersensitivity (Cytotoxic)
Reactions/antibody-dependent
 Involve activation of complement by IgG or
IgM binding to an antigenic cell.
 Antigenic cell is lysed
 Transfusion reactions:
 ABO Blood group system: Type O is
universal donor. Incompatible donor cells
are lysed as they enter bloodstream.

15. Hemolytic disease of the newborn is caused by type
II hypersensitivity reactions
When an Rh- mother carries an Rh+ fetus

16. Examples of type II
 Autoimmune hemolytic anemia
 Thrombocytopenia
 Erythroblastosis fetalis

17. Type III Hypersensitivity
(Immune Complex) Reactions
 Involve reactions against soluble antigens
circulating in serum.
 Antibody-Antigen immune complexes are
deposited in organs, activate complement, and
cause inflammatory damage.
 Glomerulonephritis: Inflammatory kidney damage.
 Occurs with slightly high antigen-antibody
ratio is present.

18. Type III (immune complex mediated)
Hypersensitivity

19. Immune Complex Mediated
Hypersensitivity

20. Examples of type III
 Serum sickness
 Arthus reaction
 Systemic lupus erythematosus (SLE)
 Post streptococcal Glomerulonephritis
 IgA nephropathy
 Rheumatoid arthritis

21. Hypersensitivity Type III Reactions
Systemic ReactionsLocal Reactions
 Arthus Reaction:
Inflammation caused
by the deposition of
immune complexes at a
localized site.
Clinical Manifestation
is :
Hypersensitivity
Pneumonitis
 Serum Sickness:
Systemic inflammatory
response to deposited
immune complexes at many
areas of body.
Clinical Manifestation is :
Fever, Urticaria, Artheralgia,
Eosinophila,
Spleenomegally, and Lymph
adenopathy

22. Type IV (delayed) Hypersensitivity
 Used to describe the signs and symptoms associated
with a cell mediated immune response.
 Results from reactions involving T lymphocytes.
 Characteristics of this phenomenon are:
 Delayed, taking 12 hours to develop.
 Causes accumulation of lymphs and
macrophages.
 Reaction is not mediated by histamine.
 Antibodies are not involved in the
reaction.

23. Type IV Mechanism
APC resident in the skin
process antigen and
migrate to regional lymph
nodes where they
activate T cells
Sensitised T cells migrate
back to the the skin
where they produce
cytokines which attract
macrophages which
cause tissue damage

24. Examples of Type IV
 Contact dermatitis
 Mantoux test
 Chronic transplant rejection

25.  An injection of tuberculin beneath the skin causes
reaction in individual exposed to tuberculosis or
tuberculosis vaccine
 Used to diagnose contact with antigens of
M. tuberculosis
 No response when individual not infected or
vaccinated
 Red, hard swelling develops in individuals
previously infected or immunized
The tuberculin response:
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26. A positive tuberculin test

27.  Cell-mediated immune response
 Results in an intensely irritating skin rash
 Triggered by chemically modified skin proteins that
the body regards as foreign
 Acellular, fluid-filled blisters develop in severe cases
Contact Dermatitis
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28. Contact dermatitis

30. Classification of Hypersensitivity
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33. Thank You