C4 Flashcards
- coined the term “complement” because it complements the action of antibody in destroying microorganisms.
Paul Ehrlich
Heat labile series of more than 30 plasma proteins
complement”
named with a (?) followed by a (?)
capital C
number
- results from the cleavage of a larger precursor by a protease
small letter
complement” example
C3a/ C3b
- designated as b
Larger fragment
- designated as a
Smaller fragment
Exception:
C2 fragments
Larger- (?), smaller fragment- (?)
C2a
C2b
Proteins and glycoproteins synthesized mainly by liver
COMPONENTS
Most circulate in the serum functionally inactive forms
COMPONENTS
Produces a cascade phenomenon where the product of one reaction is the enzymatic catalyst of the next
COMPONENTS
(?) soluble and cell-bound proteins
30
FUNCTIONS OF COMPLEMENT
- Lysis of cells, bacteria and viruses
- Opsonization
- Triggers specific cell functions, inflammation and secretion of immunoregulatory molecules
- Immune clearance: removal of immune complexes and deposition in the spleen and liver
Biological Functions
- Anaphylatoxin
- Increase Capillary Permeability
- Chemotaxis
- Virus neutralization
- Opsonization
Main Complement Component Involved Opsonization
C3b
Main Complement Component Involved Anaphylatoxin
C3a, C4a, C5a
Main Complement Component Involved Increase Capillary Permeability
Role of C2b fragment
Main Complement Component Involved Chemotaxis
C5a
Main Complement Component Involved Virus neutralization
C4
They bind to receptors on mast cells and basophils
Anaphylatoxin
Induce degranulation and release of influx mediators including histamine
Anaphylatoxin
small peptide that causes increased vascular permeability, contraction of smooth muscle, and release of histamine from basophils and mast cells.
Anaphylatoxin
Can lead to edema if complement is not controlled
Increase Capillary Permeability
Attract cells and play important role in recruitment of cells to an influx site
C5a
Enhances neutralization of viruses by homologous antibodies
C4
C3b on particles such as bacteria or an Ab-Ab complex promotes the attachment and ultimate ingestion of the particles.
C3b
CLASSICAL Initiated by:
Antigen-antibody complex
ALTERNATE/ALTERNATIVE/PROPERDIN Initiated by:
- Aggregates of IgA
- Yeast cell or zymogen
- CVF
- LPS
LECTIN Initiated by:
With mannose and other similar sugars in the cell wall
Recognition event which will initiate complement cascade
INITIATION PHASE
Classical and alternate pathway differ at this phase
INITIATION PHASE
Activation of early components culminate in activation of C3 which is the critical component
AMPLIFICATION/ ACTIVATION PHASE
Classical and alternate pathway differ at this phase
AMPLIFICATION/ ACTIVATION PHASE
Culminates in target cell lysis
MEMBRANE ATTACK PHASE
Classical and alternate pathway is the same at this phase
MEMBRANE ATTACK PHASE
Phases of Complement Activation
Initiation of Pathways
Activation of the Complement
Bonding of C1 complex (C1q, C1r, C1s) to antibodies bound to an antigen on the surface of a bacterial cell.
Classic Pathway
Contact with a foreign surface such as the polysaccharide coating of a microorganism
Alternative
Covalent bonding of a small amount of C3b to hydroxyl groups on cell surface carbohydrates and proteins.
Alternative
Activated by low-grade cleavage of C3 in plasma
Alternative
Binding of the complex of mannose binding lectin and associated serine proteases (MASP1 and MASP2) to arrays of mannose groups on the surface of a bacterial cell.
Mannose Binding
Major effector mechanisms of antibody-mediated immunity.
CLASSICAL PATHWAY
CLASSICAL PATHWAY
Principal components:
C1-C9
CLASSICAL PATHWAY
Activation:
C1, 4, 2, 3, 5, 6, 7, 8 and 9
present in the plasma in the largest quantities
C3
fixation of (?) is the major quantitative reaction of the complement cascade
C3
CLASSICAL PATHWAY
3 major stages:
- Recognition
- Amplification of proteolytic complement cascade
- Membrane attack complex (MAC)
Begins with the formation of soluble antigen-antibody complexes or with binding of antibody to antigen on a suitable target such as a bacterial cell
CLASSICAL PATHWAY
IgM or IgG
CLASSICAL PATHWAY
Ag-Ab-IgM : conformational change in Fc : exposing a binding site for C1
CLASSICAL PATHWAY
is the recognition unit that binds to the FC portion of two antibody molecules
C1qrs
C1s is activated and cleaves C4 and C2 to form (?), which is known as C3 convertase.
C4b2a
C3 convertase cleaves C3 to form (?), known as C5 convertase.
C4b2a3b
The combination of (?) is the activation unit.
C4b2a3b
(?) cleaves C5.
C5 convertase
C5b attracts (?), which bind together, forming the membrane attack complex.
C6, C7, C8, and C9
(?) polymerizes to cause lysis of the target cell.
C9
Antibody is not required
ALTERNATIVE PATHWAY
Innate immunity
ALTERNATIVE PATHWAY
ALTERNATIVE PATHWAY
4 serum proteins:
C3, factor B, factor D and properdin
Initiated by cell-surface constituents that are foreign to the host (gram + and gram – bacterial cell walls)
ALTERNATIVE PATHWAY
Factors capable of activating the alternative pathway
✓ Inulin
✓ Zymosan
✓ Bacterial polysaccharides and endotoxins
✓ Aggregated IgG2, IgA and IgE
: proteins that recognize and bind to specific carbohydrate targets
Lectins
After initiation proceeds thru action of C4 and C2 to produce C5 convertase
MANNOSE BINDING LECTIN PATHWAY
Activated by binding of mannose-binding lectin to mannose residues on glycoproteins or carbohydrates on the surface of microorganisms such as Salmonella, Listeria, Neisseria, Cryptococcus and Candida.
MANNOSE BINDING LECTIN PATHWAY
The binding of (?) to two antibody molecules activates the classical pathway, while the alternative pathway is started by hydrolysis of C3.
C1qrs
The (?) is triggered by binding of MBP to mannose on bacterial cell walls.
lectin pathway
(?) bind to form an activated C1-like complex.
MASP-1, MASP-2, and MASP- 3
(?) cleaves C2 and C4 and proceeds like the classical pathway.
MASP-2
(?) operate in the alternative pathway.
Factor B and factor D
While C3 convertase is formed differently in each pathway, (?) is a key component in each one.
C3
The C5 convertase in the alternative pathway consists of (?).
C3bBb3bP
In the classical pathway, C5 convertase is made up of (?).
C4b2a3b
After (?) is cleaved, the pathway is common to all.
C5
3 pathways: active C5 convertase to cleave C5 — [?] (initiates the final steps to form MAC)
C5a and C5b
Forms a large channel through the membrane of the target cell enabling ions and small molecules to diffuse freely across the membrane.
MEMBRANE ATTACK COMPLEX
Molecular wt.
410
C1q
Molecular wt.
85
C1r
C1s
Molecular wt.
205
C4
Molecular wt.
102
C2
Molecular wt.
190
C3
C5
Molecular wt.
110
C6
Molecular wt.
100
C7
Molecular wt.
150
C8
Molecular wt.
70
C9
Conc.(ug/mL)
150
C1q
Conc.(ug/mL)
50
C1r
C1s
Conc.(ug/mL)
300-600
C4
Conc.(ug/mL)
25
C2
Conc.(ug/mL)
1200
C3
Conc.(ug/mL)
80
C5
Conc.(ug/mL)
45
C6
Conc.(ug/mL)
90
C7
Conc.(ug/mL)
55
C8
Conc.(ug/mL)
60
C9
Binds to Fc region of IgM and IgG
C1q
Activates C1s
C1r
Cleaves C4 and C2
C1s
Part of C3 convertase (C4b)
C4
Binds to C4b—forms C3 convertase
C2
Key intermediate in all pathways
C3
Initiates membrane attack complex
C5
Binds to C5b in MAC
C6
Binds to C5bC6 in MAC
C7
Starts pore formation on membrane
C8
Polymerizes to cause cell lysis
C9
Molecular wt.
93
Factor B
Conc.(ug/mL)
200
Factor B
Binds to C3b to form C3 convertase
Factor B
Molecular wt.
24
Factor D
Conc.(ug/mL)
2
Factor D
Cleaves factor B
Factor D
Molecular wt.
55
Properdin
Conc.(ug/mL)
15-25
Properdin
Stabilizes C3bBb–C3 convertase
Properdin
Molecular wt.
200-600
MBL
Conc.(ug/mL)
0.0002-10
MBL
Binds to mannose
MBL
Molecular wt.
93
MASP-1
Conc.(ug/mL)
1.5-12
MASP-1
Unknown
MASP-1
Molecular wt.
76
MASP-2
Conc.(ug/mL)
Unknown
MASP-2
Cleaves C4 and C2
MASP-2
Lupus like syndrome; recurrent infections
C1 (q, r, or s)
Lupus like syndrome; recurrent infections; atherosclerosis
C2
Severe recurrent infections; glomerulonephritis
C3
Lupus like syndrome
C4
Neisseria infections
C5-C8
No known disease association
C9
Hereditary angioedema
C1INH
Paroxysmal nocturnal hemoglobinuria
DAF
Paroxysmal nocturnal hemoglobinuria
MIRL
Recurrent pyogenic infections
Factor H or factor I
Pneumococcal disease, sepsis, Neisseria infections
MBL
Neisseria infections
Properdin
Pneumococcal diseases
MASP-2
associated with inflammatory conditions, trauma, or acute illness
INCREASED COMPLEMENT LEVELS
Limited clinical significance
INCREASED COMPLEMENT LEVELS
Low levels of complement suggest one of the following biological effects:
• Complement has been excessively activated recently.
• Complement is currently being consumed.
• A single complement component is absent because of a genetic defect.
result from the complexing of IgG or IgM antibodies capable of activating complement
HYPOCOMPLEMENTEMIA
associated with diseases that give rise to circulating immune complexes.
HYPOCOMPLEMENTEMIA
The (?) is a series of more than 30 proteins normally found in serum that play a major role in phagocytosis and clearance of foreign antigens from the body.
complement system
While the end product of complement activation is lysis, other important events, such as (?) of monocytes and neutrophils take place along the way to enhance host defense mechanisms.
opsonization, increase in vascular permeability, and chemotaxis
Most of the proteins of the complement system are inactive enzyme precursors, or (?), that are converted to active enzymes in a very precise order.
zymogens
One means of activation is the (?), which is triggered by antigen–antibody combination and involves nine of the proteins.
classical pathway
(?) plays a major role in several disease states.
Complement
Decreased complement levels or a decline in lytic activity can indicate either (?)
hereditary deficiencies or extreme activation of the system
(?) are two conditions that result from missing or very low production of certain regulators.
Paroxysmal nocturnal hemoglobinuria and hereditary angioedema
Deficiencies of some components, especially that of C3, may cause an increased risk of (?) due to a lack of clearance of immune complexes.
lifethreatening infection or glomerulonephritis
Several laboratory assays have been devised to detect (?).
abnormal complement levels
One of these, the (?), uses 50 percent lysis of a standard concentration of antibody-sensitized sheep erythrocytes as an end point.
CH50 hemolytic assay
This measures the presence of all proteins involved in the classical pathway.
CH50 hemolytic assay
A similar assay, the (?), measures the functioning of the alternative pathway.
AH50 assay
Other assays using (?) measure levels of individual components.
RID or ELISA techniques
(?) is essential to ensure correct interpretation of laboratory testing.
Proper handling of specimens
(?) use complement as a reagent to detect the presence of antigen or antibody.
Complement fixation tests
(?) are allowed to combine with a measured amount of complement.
Antigen and antibody
Then indicator (?) are added.
sheep red blood cells
These are coated with (?) (antisheep cell antibody), and if complement has not been tied up in the first reaction, then lysis of the cells occurs.
hemolysin
Thus, (?) is a negative test, indicating that either antigen or antibody was not present.
lysis
As in all complement testing, the use of (?) is necessary for accurate results.
standards and control
