ImmunoSero Lec (Midterms - Soluble Mediators) Flashcards
Part of the innate system that helps phagocytic cells to clear pathogens, lyse foreign cells, opsonize and tag invaders for clearance, direct the adaptive immune system to the site of infection.
Complement system
Amplify inflammatory response having 30 soluble and cell bound proteins
Complement system
Heat labile substance present in normal nonimmune serum
Complement system
Complement activation is also considered pro-inflammatory in its ability to (3)
- Increase vascular permeability
- Recruit monocytes and neutrophils
- Trigger secretion of regulatory molecules that amplify the immune response
In the pro-inflammatory role, this serves as an important link between innate and adaptive immunity
complement protein
A complex series composed of 30 soluble and cell bound proteins that interact in a very specific way to enhance host defense mechanisms against foregin cells including serum proteins, serosal proteins, and cell membrane receptors
Complement protein
This is where most plasma proteins are synthesized except C1
Liver
C1 are components which are mainly produced by these cells.
Intestinal epithelial cells
Tissue composition of Factor D of Alternative Pathway
Adipose tissue
Nobel prize laureate which elucidated their nature
Jules Bordet
Coined the term “complement” because it complements the action of antibody in destroying microorganisms.
Paul Erlich
3 Complement pathways
- Classical
- Alternative
- Mannose Binding Lectin
Originally called the properdin system, because the protein properdin was thought to initiate this pathway. However, it is know that properdin’s major function is to stabilize a key enzyme complex formed along the pathway.
Alternative Pathway
Oldest pathway which is another antibody-independent means of activating complement proteins.
Mannos Binding Lectin Pathway
The major constituent of the MBL Pathway that adheres to mannose found mainly in the cell walls or outer coating of bacteria, viruses, yeast, and protozoa.
Mannos- (mannan-) binding lectin
Naming system
- Designated as “b”
- Designated as “a”
b: larger fragment
a: smaller fragment
In this complement protein, “a” is designated as the larger fragment while “b” is the smaller fragment.
C2
Number of proteins triggered by antigen-antibody combination in the Classical Pathway
9 (C1-C9)
Immunoglobulins involved in the Classical Pathway
IgM, IgG1, IgG2, and IgG3
Initiation of Classical Pathway
- Antibody binding to the pathogen
- C1 protein binding to the FC receptor of antibody
Most efficient because it has multiple binding sites thus it takes only one molecule attached to two adjacent antigenic determinants to initiate the cascade.
IgM
Number of IgG molecules that must attach to antigen within 30 to 40 nm of each other before complement can bind.
At least how many IgG molecules would it tkae to ensure that it is close enough to initiate such binding?
2 IgG molecules;
At least 1000
Within the IgG group, IgG3 is the most effective, followed by these two:
IgG 1 then IgG2
Stablizes C1q, C1r, and C1s.
Calcium
First complement component of the classical pathway to bind.
C1
The ________________ unit is the part that binds to antibody molecules, whereas the ____________________ subunits generate enzyme activity to begin the cascade.
C1q;
C1r and C1s
Composed of 6 strands that forms the 6 globular heads with collagen tailed portion. This structure has been likened to a bouquet with six blossoms extending outward
C1q
As long as this is present in the serum, C1r and C1s remain associated with C1q
calcium
Recognizes the fragment crystallizable region of two adjacent antibody molecules.
C1q
At least how many globular heads of C1q must be bound to initiate the classical pathway?
two
Binding for IgG and IgM respectively
IgG - CH2 region
IgM - CH3 region
Once this complement is activated, the recognition stage ends
C1s
This complement is extremely specific because its only known subtrate is C1s
C1r
A complement that has a limited specificity with it only subtrates being C4 and C2
C1s
Formed by C4a + C2b
C4b2a (C3 convertase)
Second-most-abundant complement protein with a serum concentration of approximately 600 ug/mL.
C4
C1s cleaves C4 to split off how many amino acid fragment called C4a?
77-amino-acid fragment
C4b binds mainly to antigen in cluster that are within this radius of C1
40 nm radius
First amplification step in the cascade (The Activation Unit)
C4b binds to antigen in cluster that are within 40 nm radius of C1
For every one C1 attached, approximately how many molecules of C4 are split and attached?
30
Closely associated with the gene for factor B (alternative pathway) on Chromosome 6
C2
True or False.
C2 has a short half-life that serves to keep the reaction localized.
True
Written as C4b2a to indicate that complex is an active enzyme by which its half-life is estimated to be between 15 seconds - 3 minutes.
C3 convertase
Major and central constituent of the complement system
C3
a powerful opsonin
C3b
Most significant step in the entire process of complement activation
Cleavage of C3 to C3b
Half-life estimation of C3b if not bound to antigen.
60 microseconds
Written as C4b2a3b
C5 convertase
When this attaches to the cell membrane, formation of the (MAC) Membrane Attack Complex begins.
C5b
Most significant biological consequences of the complement system.
Splitting of C5 and the cleavage of C3
Forms the Membrane Attack Complex
C6-C9
The MAC is the complex of
C5b-C6-C7-C8-C9
In MAC, if the complex is soluble in circulation, it is called …
sC5b-9
Functional pore size of completed MAC unit which would allow ions to pass in and out of the membrane.
70 to 100A
This form of IgM is found in plasma
Planar form
Form of IgM that will bind to the cell
Staple form
Recognition unit
C1
activation unit
C2, C4, and C3
Forms the membrane attack complex
C5b, C6-C9
Activated by recognition of surface moieties that are found on pathogens and are independent of antibodies
Lectin pathway
Proteins that bind carbohydrates (manose)
Lectin
One key lectin binds to mannose or related surgars in this manner.
Calcium-dependent manner
Plays an important role as a defense mechanism in infancy, during the intercal between the loss of maternal antibody and the acquisition of a full-fledged antibody response to pathogens.
Lectin Pathway
Acute phase protein produced in the liver that binds to mannose or related sugars
MBL
Bacteria that has mannose in their cell wall
Neisseria
Candida
Salmonella
Its deficiency is associated with neonatal pneumonia and sepsis.
MBL
MBL-associated serine proteases
MASPs
The most common MASP because it will be the one to cleave C4 and C2 to form the C3 convertase
MASP-2
Non-antibody initiated pathway that is slower than the classical pathway and stabilizes the C3 convertase.
Alternative pathway
First step in Alternative Pathway
Conversion of C3
In plasma, this is not stable.
Native C3
> A serine protease
Its only substrate is bound Factor B
Lowest (2 ug/ml)
It cleaves Factor B into two pieces: Ba and Bb
Factor D
> Alternative pathway convertase
Capable of cleaving additonal C3 into C3a and
C3b
C3bBb
Has a high affinity for C5 and exhibits C5 convertase activity
C3bBb3bp
True or False.
C3bBb cannot cleave C5, and is only efficient at cleaving C3.
False. C3bBb can also cleave C5, but it is much more efficient at cleaving C3.
Where all the pathways meet.
C3
> Inactivates C1 by binding to the active sites of C1r and C1s
> Inactivates MASP-2 binding to the MBL-MASP
complex
C1 inhibitor (C1-INH)
A serine protease that inactivates C3b and C4bs only when bound to these regulators:
C4 binding protein (C4BP)
Complement receptor type 1 (CR1)
Membrane cofactor protein (MCP)
Decay-accelerating factor
Factor 1
Causing the cessation of the classical pathway
When C4BP attaches to cell-bound C4b (it can dissociate it from C4b2a complexes)
Also known as CD35, which is a large polymorphic glycoprotein found mainly on peripheral blood cells, including neutrophils, monocytes, macrophages, erythrocytes, eosinophils, B lymphocytes, some T lymphocytes, and follicular dendritic cells.
Complement receptor type 1 (CR1)
Ability of cells to bind complement coated particles
Immune adherance
Also known as CD46; found on virtually all epithelial and endothelial cells except erythrocytes
Membrane cofactor protein (MCP)
> third main receptor, and it has a wide tissue distribution
> found on peripheral blood cells, on endothelial cells and fibroblasts, and on numerous types of epithelial cells
> capable of dissociating both classical and alternative pathway C3 convertases
Decay-accelerating factor
Its presence on host cells protects them from bystander lysis and is one of the main mechanisms used in discrimination of self from nonself, because foreign cells do not possess this substance.
DAF
Acts by binding to C3b, preventing the binding of Factor B and as a cofactor that allows Factor I to break down C3b
Factor H
Accelerates the dissociation of the C3bBb complex because when this binds to C3bBb, Bb becomes displaced.
Factor H
Vitronectin
S protein
CD59, also acts to block formation of the MAC and is widely distrubuted in all cells.
Membrane Inhibitor of Release Lysis (MIRL)
Biological functions of Complement Proteins
- Amplifying the inflammatory response
- Antigen presentation
- B cell activation
- Immunologic memory
Effector molecules that causes increased vascular permeability, contraction of smooth muscle, and release of histamine and mast cells.
Anaphylatoxin
Most potent anaphylatoxin
C3a and C5a
Direct cells to the source of antigen concentration
Chemotaxin
Most common chemotaxin
C5a
Most common complement deficiency
C2
Most serious complement deficiency
C3
These individuals may be more prone to recurrent streptococcal and staphylococcal infections.
C2-deficient individuals
Individuals with this deficiency are prone to developing severe, recurrent life-threatening infections with encapsulates bacteria and may also be subject to immune complex diseases which can be lodged in the kidney and result in glomerulonephritis
C3 deficiency
Its deficiency is associated with lupuslike syndrome
C4 deficiency
Its deficiency has no known disease association
C9 deficiency
Its deficiency is associated wtih neisseria infections
C5-C8
Properdin
Its deficiency is associated with paroxysmal nocturnal hemoglobinuria
DAF and MIRL
Its deficiency is associated with recurrent pyogenic infections
Factor H or Factor I
Its deficiency is associated with pneumococcal diseases
MASP-2
Its deficiency is associated with hereditary angioedema
C1INH (C1 inhibitor)
Cells are subject to lysis by means of the bystander effect once the complement system has been triggered
DAF Deficiency
Acquired autoantibody
C3NeF (C3 Nephrotic Factor)
Medium used for radial immunodiffusion into which specific antibody is incorporated.
Agarose gel
This serves as the antigen in radial immunodiffusion.
Serum
Radial immunodiffusion is commonly performed for this complement
C3
Routinely measured in most clinical labs
C3 and C4
Measures concentration according to the amount of light scattered by a solution containing a reagent antibody and a measured patient sample
Nephelometry
Test with high degree of accuracy
Nephelometry
Measurement of C1 inhibitor (C1-INH)
ELISA
Measures the amount of patient serum required to lyse 50% of a standardized concentration of antibody-sensitized sheep erythrocytes
CH50
Tested by doing a serial dilution adding it to sensitized sheep red blood cells.
CH50
Tubes in CH50 are then incubated at what temperature?
37C
Best screen for complement abnormalities
ELISA
alternative pathway assay
AH50
Added to the buffer for AH50
Magnesium Chloride & Ethlylene Glycol Tetraacetic Acid (EGTA)
Can detect C3bBbP or C3bP
ELISA
In one test system, what coats the strip for classical, alternative, and mannose-binding lectin pathway?
Classical -IgM
Alternative - lipopolysaccharide
Mannose-binding Lectin - mannose
If not tested within 1 to 2 hours, serum should be
frozen or placed on dry ice
Both the CH50 and AH50 are low
Terminal pathway
CH50 low, AH50 normal
Classical Pathway
CH50 normal, AH50 low
Alternative
secrete specific antibodies
B lymphocytes
secrete soluble mediators, such as interleukin-2 (IL-2) and other ILs, granulocytemonocyte, colony-stimulating factor (GM-CSF), interferon-γ (IFN-γ) and tumor necrosis factor-β (TNF-β)
T lymphocytes
lymphocytes that secrete IFN-α 4
NK lymphocytes
secrete IFN-α, IL-1, and other ILs, TNF-α, and GM-CSF and monocyte colony-stimulating factor (M-CSF)
Monocytes an macrophages
Induces fever, proinflammatory
IL-1
Induces production of CRP
IL-6
Potent stimulator of neutrophils in chemotaxis
IL-8
Enhances NK cell function
IL-12
Mediate actopms between leukocytes
Interleukins
Interferes with viral replication
Interferon
Principal mediator of the acute inflammatory response to gram-negative bacteria & other infectious microbes
Tumor necrosis Factor
TNF produced by macrophages, lmphocytes and NK cells when encountering bacteria, viruses, tumor cells, toxins and complement protein C5a
TNF-a
TNF produced by CD4 and CD8 positive cells after
exposure to specific antigen
TNF-Beta
a cytokine that interacts with a tyrosine kinase membrane receptor, the protein product of the cellular oncogene c-kit
Stem cell factor
may also play a role in** sustaining the viability and proliferative capacity of immature T cells** in the thymus and mast cells in mucosal tissues
Stem cell factor
provide a link between the lymphoid and hematopoietic systems
Colony stimulating factor
identified as products of virally transformed cells
Transforming Growth Factor
It inhibits the proliferation and differentiation of T
cells and the activation of macrophages
Transforming growth factor
These factors were found to induce phenotypic transformation in nonneoplastic cells
Transforming Gtowth Factor
