1.1.2 Type III Hypersensitivity Reactions

Question 1

How long do type III hypersensitivity reactions take to develop?

Answer 1

3-8 hours after re-exposure

Question 2

What do type III hypersensitivity reactions involve?

Answer 2

Immune complexes between IgG or Igm and soluble antigens

Question 3

What do type III hypersensitivity reactions target?

Answer 3

Soluble antigens
-Foreign (infection)
-Endogenous (self antigens)

Question 4

How is damage caused by type III hypersensitivity reactions?

Answer 4

Deposition of immune complexes in blood vessels

Question 5

What are the key factors affecting immune complexes in type III reactions?

Answer 5

• Complex size - small and large ICs cleared by RES, intermediate are the problem
• Persistance of antigen - chronic infection or self antigens
• Host response - low affinity antibody or complement deficiency
• Local tissue factors - haemodynamic, physiochemical

Question 6

What happens in complement deficiency?

Answer 6

C2 and C3 protein absent

C3 binds to immune complex and RBCs have a C3b receptor, RBCs are then taken to the spleen and cleared

In a compliment deficiency there is not adequate clearance of these immune complexes

Question 7

Where do immune complexes deposit?

Answer 7

Blood vessels
Joints
Kidney
Skin
Heart

Question 8

What is the immune mechanism behind type III hypersensitivity reactions?

Answer 8

1. Intermediate-sized immune complexes deposited in the tissue
2. Complement activated
3. Neutrophil chemotaxis (movement towards chemical stimulus)
4. Neutrophil adherence and degranulation

Question 9

What are 3 examples of type III hypersensitivity reactions?

Answer 9

• Rheumatoid arthritis
• Glomeurlonephritis
• Systemic lupus erythematosus

Question 10

What is the antigen in rheumatoid arthritis?

Answer 10

Fc portion of IgG

Question 11

What are the features of rheumatoid arthritis?

Answer 11

• Articular and extra-articular features
• Episodes of inflammation/remission
• Rheumatoid nodules
• Joint deformity

Question 12

Prognosis factors of rheumatoid arthritis

Answer 12

Poor prognosis factors:
-< 30 year-old
-High titre of RF
-Female
-DR4 allele
-Joint erosions

Question 13

What is the antigen for glomerulonephritis?

Answer 13

Infectious microbes e.g. bacterial endocarditis or hepatitis B

Question 14

What is the antigen for systemic lupus erthematosus?

Answer 14

Double stranded-DNA

Question 15

Systemic lupus erythematosus features

Answer 15

• Most prevalent immune complexes disease
• Female:Male 9:1
• 40-60% of patients have cardiac, respiratory, renal, joint and nuerological features
• Repeated miscarriage
• Typical malar rash (butterfly rash)

Question 16

What is an immune complex?

Answer 16

Multi-molecular complex of antibodies and bound antigens