Type III Hypersensitivity reactions Flashcards
1
Q
What is an immune complex?
A
Formed by binding of antibody to antigen with or without complement proteins
2
Q
How can small immune complexes cause type II reactions?
A
Small immune complexes form when a soluble antigen is in excess, if it isn’t cleaved and is deposited in tissues it can cause type III reaction
3
Q
What can cause immune complex formation?
A
- Persistent infection from microbial agents
- Autoimmunity
- Inhaled antigens
4
Q
Which antibody primarily mediates type III reactions?
A
IgG
5
Q
How can immune complexes trigger inflammation?
A
- Interact with basophils and platelets and induce vasoactive amine production
- Induce C3a which activates mast cells which produce chemotactic factors
- IL-1 and TNF-alpha production by macrophages
- Increase vascular permeability
6
Q
What does an increase in vascular permeability cause in type III reactions?
A
- Leads to endothelial cells retracting
- Basement membrane is exposed
- Deposition of immune complexes onto basement membrane occurs
7
Q
What happens when immune complexes are deposited?
A
- Deposited complexes continue to trigger C3a and C5a formation
- Platelets aggregate on exposed collagen and cause microthromi
- Frustrated phagocytosis occurs causing local tissue damage
8
Q
What does complement deficiency lead to in context of immune complexes?
A
Deficiency leads to formation of relatively insoluble complexes which may deposite in tissues
