1) Hypersensitivity Reactions

Question 1

Define Hypersensitivity

Answer 1

Antigen Specific immune response that are either inappropriate or excessive and result in harm to host.

Question 2

List some exogenous antigens which can cause hypersensitivity

Answer 2

> Non infectious Substances
Infectious Microbes => Sepsis
Drugs => Penicillin

Question 3

List some endogenous antigens which can cause hypersensitivity

Answer 3

> Infectious Microbes (Mimicry)

> Self antigens (Auto - immunity)

Question 4

List the different types of Hypersensitivity Reactions

Answer 4

Type I (Immediate) => Allergy (IgE)
Type II => Antibody Mediated (IgG)
Type III => Immune Complex Mediates (IgG)
Type IV (Delayed) => Cell Mediated

Question 5

What are the two phases that leads to Hypersensitivity Reactions ?

Answer 5

> Sensitisation Phase
- 1st encounter with the antigen
- Activation of APCs and memory effector cells.
Effector Phase
- Pathological reaction upon re exposure to the same antigen and activation of memory cells of the adaptive immunity

Question 6

How does Type 2 Hypersensitivity Reactions cause different outcomes.
> Tissue / Cell Damage
> Physiological Change

Answer 6

Tissue / Cell Damage 
> Complement Activation 
- Cell Lysis 
- Neutrophil Recruitment (C3a / C5a)
- Opsonisation (C3b) 
> Antibody Dependent Cell Cytotoxicity (NK Cell) 

Physiological Changes 
> Receptor Stimulation 
- Graves' Disease 
> Receptor Blockade 
- Myasthenia Gravis

Question 7

Give an Example of disease caused by Type II Hypersensitivity (IgM)
> Immune Mechanism

Answer 7

Haemolytic Transfusion Reaction
=> Shock, Kidney Failure, Circulatory Collapse and Death
Immune Mechanism:
> Incompatibility of ABO or Rhesus D Antigen
> Donor RBC is destroyed by recipient Immune System by Naturally occurring IgM

Question 8

Give an Example of disease caused by Type II Hypersensitivity (IgG)
> Immune Mechanism

Answer 8

Haemolytic Disease of New born Disease
Immune Mechanism:
> Rh + Father and Rh - Mother first child is Rh+ (Sensitisation Phase)
> During Delivery Antigens from fetus can enter maternal blood
> Anti Rh Antibodies are produced
> If Mother becomes pregnant again with another Rh+ Fetus, antibodies will cross the placenta and damage fetal RBC

Treatment => RhoGam Immunoglobulin administer 72 hours after birth of first child

Question 9

List the Therapeutic Approaches for Type II Hypersensitivity

Answer 9

1) Anti inflammatory Drugs
- Complement Activation
2) Plasmapheresis
- Circulating Antibodies and Inflammatory Mediators
3) Splenectomy
- Opsonisation
4) IV Immunoglobulin
- IgG Degradation
5) Graves’ - Anti thyroid medication
6) Myasthenia Gravis - Pyridostigmine - Acetylcholiesterase inhibitor

Question 10

What serious complication can occur in Haemolytic Disease of the Newborn ?

Answer 10

Kernicterus - Permanent Neurological Damage in the babies that survive

Question 11

What test can you carry out to diagnose HDN ?

Answer 11

Coombs Test

Question 12

What key factors can affect IC Pathogenesis ?

Answer 12

> Complex Size

• Small and Large ICs cleared
• Intermediate size ICs

> Host Response

• Low affinity Antibody
• Complement Deficiency

> Local Tissue Factors

• Haemodynamic Factors
• Physiochemical Factors

Question 13

How does Type III Hypersensitivity cause damage in patients ?

Answer 13

Immune complexes between IgG and IgM and antigens.
Deposited in Host tissue 
-Joints
-Kidney 
-Small Vessels 
-Skin

Question 14

Outline the immune mechanism of Type III hypersensitivity ?

Answer 14

1) Intermediate sized Immune Complex deposited in the tissue
2) Complement Activated
3) Neutrophil Chemotaxis
4) Neutrophil adherence and degranulation

Question 15

List 3 Examples of diseases caused by type III hypersensitivity

Answer 15

Rheumatoid Arthritis (Self Antigen)
Glomerulonephritis (Infectious)
SLE

Question 16

What are some common symptoms of SLE

Answer 16

Systemic:

• Low Grade Fever
• Photosensitivity

Physiological

• Fatigue
• Loss of Appetite

Mouth Ulcers 
Muscle Aches 
Butterfly Rash 
Inflammation of Pleura and Pericardium 
Arthritis 
Poor Circulation

Question 17

What does Type IV hypersensitivity involve ?

Answer 17

Lymphocytes and Macrophages

Question 18

Give examples of diseases which is caused by Type IV hypersensitivity to Exogenous Antigens

Answer 18

Contact Hypersensitivity:
> 48 - 72 hours post exposure 
- Nickel 
- Poison Ivy 
- Organic Chemicals 
> Epidermal Reaction 

Granulomatous Hypersensitivity 
> 21-48 post exposure 
- TB
- Leprosy 
- Schistosomiasis 
- Sarcoidosis 
> Tissue Damage

Question 19

Give examples of disease caused by Type IV Hypersensitivity to Endogenous Antigens

Answer 19

• Pancreatic Islet Cells => Insulin Dependent DM
• Thyroid Gland => Hashimoto’s
• Fc portion of IgG => RA

Question 20

What therapy is used to treat Type III and IV ?

Answer 20

Anti inflammatory drugs 
- Non Steroidals
- Corticosteroids (Predisnolone)
- Steroid Sparing Agents:
> Azathioprine 
> Mycophenolate Mofetil 
> Cyclophosphamide 

MAB

Question 21

Outline the features of Myasthenia Gravis
> Signs and Symptoms
> Pathophysiology
> Treatment

Answer 21

Signs and Symptoms:
> Muscle Paralysis
> Ptosis
> Diplopia

Pathophysiology
> AchR - Antibodies are produced which circulate the blood, which binds to Nicotinic Receptors on the muscle end plates
> This prevents Ach from binding and thus no Depolarisation of muscle end plates

Treatment:
> Pyridostigmine - Acetylcholinesterase inhibitor that binds to Acetylcholinesterase and thereby reduces binding and degradation of Ach at the muscle end plate and thus increases concentration prolonging its action