4. Complement Flashcards
Complement System: Roles
1. Direct lysis of cells, bacteria and enveloped viruses 2. Assist with Opsonization to facilitate phagocytosis 3. Produce peptide fragment split products which can mediate inflammatory and immune responses
Complement System: Definition
The complement system a) A series of proteins (called factors) b) Amplifies the immune response c) Factors circulate in inactive forms d) Upon activation they attach in an exact sequence
(1) Recognition (C1)
(2) Enzymatic activation (C2-4)
(3) Membrane attack (C5 – 9)
Complement: What is the end result?
Destruction of the membrane at the site of the activation (CELL LYSIS)
Classical Pathway (Ag-Ab complex)
1-C4-C2-C3-C5->C9
** Requires calcium
** Requires 2 or more IgG molecules or 1 IgM molecule
** Detection of complement bound to the RBC membrane - In vivo vs In vitro (anti-C3bC3d)
•Specimen
Fresh source of complement – Red Top tube
Calcium - EDTA chelates Ca+
Alternate Pathway
Contact with a surface such as the polysaccharide coating of a bacteria (C3-C5->C9 )
Lectin Pathway
Activated by mannose binding proteins bound to macrophages.
Membrane Attack Complex is the same for both – the binding of C3b is
the pivotal stage of the pathway
** C3b is cleaved to C3d – which is detected in
** Anti – Complement reagents
Why is the complement system important in BB?
Leads to destruction of the organism or cell
e.g. Hemolytic RXNs can cause death
Poor therapeutic response
Complement System: Effects
a) Cytolysis or hemolysis
b) Cell activation
c) Opsonization (makes cells easier to phagocytize)
Heat Lability: Meaning
Inactivation of complement - Heat-labile
* * Storage of specimens important * * Think about VNA collected specimens
Inhibitors
- C1 inhibitor
- Factor H
- Factor I
- C4-binding protein (C4BP)
- Anaphylatoxin inhibitor
- Anaphylatoxin inactivator
- MAC Inhibitor
- C3 Nephritic Factor (NF)
