Type 3 Hypersensitivity

Question 1

Which type of immunoglobulin is seen in type 3 hypersensitivity reactions?

Answer 1

IgG

Question 2

What mediates type 3 hypersensitivity reactions?

Answer 2

Immune complexes

Question 3

What makes up immune complexes?

Answer 3

Antibody (IgG) + Soluble antigen

This antigen is NOT bound to a cell

Question 4

What must the antigen be to make up the immune complex?

Answer 4

Soluble

Polyvalent

Question 5

Which immune complexes are likely to deposit?

Answer 5

Small - because they’re not picked up by the immune system

Question 6

where do immune complexes cause damage?

Answer 6

At the site of deposition, NOT the site at which they were made

Question 7

How long do symptoms take to show?

Answer 7

Hours - longer than type 1 and type 2 hypersensitivity reactions because immune complexes take a while to form.

Question 8

What type of antigen can make an immune complex?

Answer 8

Infectious
Environmental
Auto

Question 9

How are the immune complexes broken down in NORMAL physiology?

Answer 9

• The complement system breaks them into smaller chunks.
• The smaller chunks are carried by complement receptor 1 (CR1) which is bound to RBCs and are taken to phagocytes.

When this doesn’t happen we get type 3 hypersensitivity

Question 10

What type of immune response is type 3 hypersensitivity?

Answer 10

Innate

Question 11

How does this cause farmers lung?

Answer 11

The person has IgG against mould protein

If its inhaled then immune complexes are made, these are insoluble and form in the long tissue

Question 12

What type of infection commonly causes immune complex formation?

Answer 12

Hep B infection

Streptococcus infection

Question 13

How are type 3 hypersensitivity reactions mediated?

Answer 13

By immune complexes

Question 14

What is the pathophysiology of type 3 hypersensitivity reactions?

Answer 14

• Small complexes aren’t removed so they deposit into the basement membrane layer of blood vessels
• Once in the blood vessel they activate the compliment system
• The complement system tries to get neutrophils to phagocytose the immune complex and when it doesn’t the neutrophils degranulate and dump enzymes which cause inflammation and tissue necrosis and fluid leaking and vasculitis
• This cycle repeats

Question 15

What are common examples of type 3 hypersensitivity reactions?

Answer 15

Glomerulonephritis (slow developing renal failure)
Nephritis (fast developing renal failure)
Arthritis
Systemic lupus erythematosus

Question 16

What are the main differences between type 2 and type 3 hypersensitivity reactions?

Answer 16

Type 2:
Antibodies attach to antigens that are ATTACHED to cell walls
Complement proteins are used in small amounts
symptoms are related to where the attaching happens

Type 3:
Antibodies attach to antigens that are NOT attached to cell walls
Complement proteins are used in large amounts
symptoms are related to where the immune complex is deposited, not where its made