Hypersensitivity Reactions

Question 1

Inappropriate/ exaggerated immune responses to •Harmless environmental antigens •Infections •Auto-antigens
causing tissue damage.
Is?

Answer 1

Hypersensitivity

Question 2

Four types according to mechanism of tissue damage ?

Answer 2

Type I (Immediate/ anaphylactic) “IgE- mediated” • 
Type II (cytolytic) ”IgG/ IgM   - mediated” 

Type III (immune-complex mediated) ”IgG/IgM-mediated

Type IV (delayed /cell-mediated)

Question 3

Exaggerated immune responses to harmless environmental antigens (allergens).
?

Answer 3

Type “I” hypersensitivity

Immediate/Anaphylactic

Question 4

Mediated by IgE ?

Answer 4

Type “I” hypersensitivity

Immediate / anaphylactic

Question 5

degranulation of Mast cells and eosinophils ?

Answer 5

Type “I” hypersensitivity

Immediate/ anaphylactic

Question 6

ffects are felt within minutes of exposure

Answer 6

Type “I” hypersensitivity

immediate hypersensitivity”

Question 7

Type” I” hypersensitivity

Mechanism: ?

Answer 7

A- Sensitization (1st Exposure):

B- Re-exposure to the same allergen:

Question 8

Type” I” hypersensitivity

Mechanism: A- Sensitization (1st Exposure): Normally, antigenic stimulation ? And condition ?

Answer 8

production of extremely low levels of IgE.
Certain individuals have a genetic predisposition to allergy, respond to certain antigens (allergens) by forming large amounts of IgE. ●IgE molecules bind to Fc receptors on mast cells & basophils
●Thus, 1st exposure to an allergen →
sensitization of Mast cells & Basophils

Question 9

1st exposure to an allergen →

sensitization of ?

Answer 9

Mast cells & Basophils

Question 10

Type “I” hypersensitivity

Mechanism: B- Re-exposure to the same allergen: ?

Answer 10

Antigen binds 2 adjacent IgE  molecules on
mast cells (cross-linking)   → Degranulation of mast cells        “release granules and mediators”.

Degranulation: release 2 kinds of mediators:
• Preformed mediators:
◦
Histamine and platelet activating factor (PAF)

Question 11

Which type of hypersensitivity and clinical form? symptoms are localized in one organ or system Urticaria (+ itching) Gastrointestinal symptoms
Bronchial asthma

Answer 11

Type “I” hypersensitivity Clinical Forms

1. Localized form (Atopy):

Question 12

Type and clinical form? insect venom (e.g., honey bee sting) Symptoms: ● Itching, severe bronchoconstriction and hypotension

shock

Answer 12

Type “I” hypersensitivity Clinical Forms

II. Systemic anaphylaxis:

Question 13

Detection of the antigen to which the individual is sensitive

extracts of various antigens are introduced into the skin of the patient.
Positive cases show
a wheal and flare reaction that appears
within 15-25 min.

Answer 13

Type “I” hypersensitivity Diagnosis

1- Skin test:

Question 14

Type “I” hypersensitivity Diagnosis through ?

Answer 14

1- Skin test

2- Measurement of serum levels of total IgE and IgE specific for a particular allergen.

Question 15

Mediated by IgG / IgM antibodies reacting with Cell-bound antigen (surface antigen).
?

Answer 15

Type “II” hypersensitivity / cytolytic / cytotoxic

Question 16

Mechanism of tissue damage 1. Complement activation
➢Lysis of target cells
2. Antibody-dependent cell-mediated cytotoxicity (ADCC) through the action of natural killer (NK) cells.
3. Opsonization of target cells
?

Answer 16

Type “II” hypersensitivity Mechanism

Cytotoxic/ cytolytic

Question 17

Type of hypersensitivity? 
Transfusion reactions        (Blood group ABO incompatibility).

Answer 17

Type 2 cytotoxic

Question 18

Hemolytic disease of the newborn (Rh incompatibility)

Type of hypersensitivity?

Answer 18

Type 2 cytotoxic

Question 19

A drug may become attached to a cell surface (e.g., RBCs/platelets) Antibodies to the drug reacting at the cell surface lead to destruction of the cell in presence of complement

Type hypersensitivity?

Answer 19

Type 2 hypersensitivity

Question 20

Autoimmune diseases
e.g., Autoimmune hemolytic anemia
(autoantibodies to an individual’s own red blood cells)
Gave’s Disease (antibodies against TSH receptors”agonist effect”)
4. Graft rejection

Type of hypersensitivity?

Answer 20

Type 2 cytotoxic

Question 21

When antibodies combine with their specific antigen,
immune complexes are formed
Type of reaction ?

Answer 21

Type “III” hypersensitivity IMMUNE-COMPLEX

Question 22

Antibodies (IgG or IgM) formed against ?

Answer 22

Type “III” hypersensitivity immune complex

Question 23

Formation of soluble immune complexes antigen and IgG / IgM.

Immune complexes penetrate the endothelium of blood vessel walls & become deposited on the vascular basement membrane.

Complement is activated
& C3a and C5a (anaphylatoxins) are released Platelets are aggregated →
Type of hypersensitivity?

Answer 23

Type “III” hypersensitivity immune complex

Question 24

Post-streptococcal glomerulonephritis / Autoimmune diseases e.g., SLE (systemic lupus erythematosis) / Graft rejection
Ex of ?

Answer 24

Type “III” hypersensitivity / immune complex

Question 25

Exaggerated cell-mediated immune response ?

Answer 25

Type “IV” hypersensitivity : delayed

Question 26

Antibodies have NO role

The main cell involved is the activated Th1

Answer 26

Type “IV” hypersensitivity delayed

Question 27

Sensitized Th1 cells recognize antigens and release •pro-inflammatory cytokines.?

Answer 27

Type “IV” hypersensitivity Mechanism

Question 28

Tuberculin skin test (TST):      A small amount of the antigen, purified
protein derivative (PPD) of tubercle bacilli, is injected intradermally into a person.

Interpretation of results: after 48-72 hours
This induration is due to accumulation of macrophages and lymphocytes.
(diameter !!)

Type of hypersensitivity?

Answer 28

Type “IV” hypersensitivity

Question 29

Granuloma formation

Type of hypersensitivity?

Answer 29

Type “IV” hypersensitivity Examples