Hypersensitivity 3

Question 1

what is a type 3 hypersensitivity reaction?

Answer 1

small soluble immune complexes

small soluble molecules + IgG deposited in the walls of small blood vessel or alveoli of the lungs

Question 2

give 4 examples of type 3 hypersensitivity

Answer 2

Arthus phenomenon

serum sickness

rheumatoid arthritis

SLE = systemic lupus erthematosus

Question 3

type 3 hypersensitivity is an immune complex disease caused by?

Answer 3

immune complexes formed from IgG and soluble antigens

Question 4

what are the 2 inflammatory mechanisms in type 3?

Answer 4

complement activation

• anaphylatoxins
• chemotactic factors

neutrophils attracted

• difficult to phagocytose tissue-trapped complexes
• > frustrated phagocytosis leads to tissue damage

Question 5

what happens in the early response?

Answer 5

little antibody + excess antigen

small immune complexes are formed that don’t fix complement and aren’t cleared from the circulation

Question 6

what happens in the late response?

Answer 6

lots of antibody + little antigen

larger immune complexes are formed that can fix complement and are cleared from the circulation via neutrophils

Question 7

explain what happens in Systemic Lupus Erythematosus

Answer 7

1. small immune complexes bind to surface of vascular tissues
2. activates complement locally
3. release of anaphylatoxins

-> increase vascular permeability
-> fluid leaks out
= edema

3. also release chemokine
   - > attract neutrophils which fail to phagocytose

-> lysosomal enzymes released from granules
= tissue damage

Question 8

how does SLE effect the kidneys and joints?

Answer 8

people make antibodies against all cellular antigens e.g. DNA etc

immune complexes circulate and clog up kidneys
-> can't get into urine 
-> complement activation 
-> neutrophils attack kidney 
= inflammation 

immune complexes also accumulate in the joints

Question 9

describe the process of Arthus reaction

Answer 9

1. locally inject antigen in immune individual with IgG antibody
2. local immune-complex formation
3. activation of complement releases inflammatory mediators
   = C5a, C3a, C4a
   -> attract neutrophils
4. local inflammation, movement of fluid + protein into tissue, and blood vessel occlusion

Question 10

how do you get serum sickness?

Answer 10

antigens in certain medications and antiserums cause the immune system to react

the antigens are from non-human sources

Question 11

describe what happens in serum sickness e.g. anti-venom

Answer 11

1. injected with foreign serum proteins
2. foreign antibodies destroy anti-venom antigens
3. foreign anti-venom antibodies now treated as antigens
4. self antibodies produced against anti-venom antibodies
5. leads to vasculitis = inflammation of blood vessels

Question 12

how are antivenoms produced?

Answer 12

1. extract venom from snakes
2. inject low dose into horses
3. horses produce antibodies against venom
4. collect horse blood
5. purify IgGs

(can remove Fc region of antibodies
-> limits epitopes)

Question 13

what are the 3 types of diseases resulting from immune complexes?

Answer 13

persistent infection e.g. TB

• microbial antigens
• > deposition of immune complexes in kidneys

autoimmunity e.g. SLE

• self antigens
• > deposition of immune complexes in kidneys, joints, arteries + skin

extrinsic factors e.g. Farmer’s lung

• environmental antigens
• > deposition of immune complexes in lungs