Laboratory Activity 3a – Basic Concepts of Antigen, Antibody, and Complement Flashcards
A substance with the ability to combine with an antibody
ANTIGEN
• The ability of the antigen to react specifically with the antibodies or cells it provoked
Specific Reactivity
• The ability to provoke an immune response by stimulating the production of antibodies, proliferation of specific T cells, or both
Immunogenicity
• Substance that is capable of inducing an immune response
Immunogen
• No immunogenicity but has reactivity
Hapten
Two (2) kinds of haptens :
o Simple or nonprecipitating
o Complex or precipitating
Can combine with antibody; cannot produce precipitates
o Simple or nonprecipitating
Can combine with the antibody; produces precipitates
o Complex or precipitating
• Larger molecules attached to haptens that confer new antigenic specificities
Carrier/ Schlepper Molecules
o Capable of stimulating antibody synthesis in the host and can also react with homologous antibodies
Complete antigen
o Bacterial cells and proteins
Complete antigen
o Cannot by themselves stimulate an immune response
Hapten/Incomplete Antigen
o Can react specifically with homologous antibodies
Hapten/Incomplete Antigen
• Substance produced in response to antigenic stimulation that is capable of specific interaction with provoking immunogen
ANTIBODY or IMMUNOGLOBULIN (Ig)
ANTIBODY or IMMUNOGLOBULIN (Ig) General functions:
o Neutralize (?)
o Facilitate (?) and kill microbes
o Combine with antigens on cellular surfaces and cause the destruction of these cells either (?) (outside of the blood vessels within the mononuclear-phagocyte system) or (?) (within the blood vessels through the action of the complement)
toxic substances
phagocytosis
extravascularly; intravascularly
o A four-chain polypeptide unit that consists of two (2) heavy chains and two (2) light chains held together by disulfide bonds
Basic structure
4 polypeptide chain:
• 2 heavy chains: each consists of about _____ amino acids
• 2 light chains: each consists of about _____ amino acids
450
220
are always of the same type
The two (2) heavy chains
o They determine the immunoglobulin class: α, γ, δ, ε, µ
Heavy chains
o κ or λ
Light chains
o Both (?) are found in all classes of immunoglobulins, but only one type is present in a given molecule
κ or λ
o Holds each light chain to a heavy chain
Disulfide bonds
o Link the mid-region of the two heavy chains
Disulfide bonds
o Fragment antigen-binding
Fab fragment
o Consists of one (1) light chain and one-half (½) of a heavy chain
Fab fragment
o The intact immunoglobulin has (?), each representing one (1) antigen binding site
two (2) Fab fragments
o Fragment crystalline
Fc fragment
halves of the two heavy chains
carboxy-terminal end
o This portion of the molecule has no antigen binding ability
Fc fragment
o The carboxy-terminal end of the immunoglobulin molecule, where the amino acid sequence is the same for all chains of that type
Constant region
o Responsible for the type and antigen-antibody reaction that occurs
Constant region
o (?) of heavy chain differs from one antibody class to the other
Constant region
o The amino-terminal end of the immunoglobulin molecule, where the amino acid sequence varies
Variable region
o This part of the molecule is responsible for the specificity of a particular immunoglobulin
Variable region
Variable region is also known as the
ANTIGEN-RECOGNITION UNITS
o Different for each antibody molecule
Variable region
o Regions within the variable region that actually form the antigen-binding site
Hypervariable region
o Through changes in the (?), an immense diversity of antigen-binding sites can be created
Hypervariable region
o number of binding sites
Valence
o The flexible portion of the heavy chain, located between the first and second constant regions
Hinge region
o This allows the molecule to bend to let the two (2) antigen-binding sites operate independently
Hinge region
o A glycoprotein that serves to link immunoglobulin monomers together
Joining chain
Joining chain is only found in __________ and _________________________
IgM and IgA2
• Predominant immunoglobulin in humans comprising approximately 75-80% of the total serum immunoglobulins
IgG
• 7S molecule with a molecular weight (MW) of approximately 150,000 Daltons
IgG
• Made up of one basic structural unit known as a monomer consisting of two heavy and two light chains, which may be kappa or lambda (but not both)
IgG
• Has the longest half-life, approximately 23-25 days
IgG
• Functions of IgG:
o Providing (?) for the newborn
o (?) of the complement
o (?)
o (?) of toxins and viruses
o Participation in (?) reactions
immunity
Fixation
Opsonization
Neutralization
agglutination
• Most primitive; first to appear in phylogeny and the last to leave in senescence
IgM
• First to appear after a primary antigenic stimulus
IgM
• Made up of five basic structural units (pentamer) in circular arrangement, 10 heavy chains and 10 heavy light chains
IgM
• Possess J chain (MW: approximately 15,000 Daltons)
IgM
• 19S molecule with a MW of approximately 900,000 Daltons
IgM
IgM Functions:
o Complement fixation .
o Agglutination
o Opsonization
o Neutralization of toxins
• In the serum, it primarily appears as a monomer
IgA
• is also found as a dimer in body secretions along the respiratory and intestinal mucosa and in milk, saliva, tears and sweat
IgA (IgA2)
• The dimer consists of two monomers held together by a J chain
IgA
is synthesized in the plasma cells found mainly in mucosal-associated lymphoid tissue (MALT) and it is released in dimeric form
Secretory IgA
Secretory component
Secretory IgA
is found on the surface of immunocompetent but unstimulated B lymphocytes
IgD
• Postulated to be an anti-idiotypic antibody (antibody to antibody) and as such may be involved in the feedback mechanism to switch off B cells
IgD
• Function of IgD:
o Immunoregulation
• Least abundant immunoglobulin in the serum
IgE
• Heat-labile antibody
IgE
o Mediates some types of hypersensitivity (allergic reaction), allergies, and anaphylaxis and is generally responsible for an individual’s immunity to invading parasites
IgE
o Binds strongly to a receptor on mast cells and basophils and together with antigen, mediates the release of histamine and heparin from these cells
IgE
• A defensive system consisting of over 30 proteins produced by the liver and found in circulating blood serum
COMPLEMENT SYSTEM
o Serum proteins that interact to enhance the host defense reactions
COMPLEMENT SYSTEM
o Most are inactive enzyme precursors that are converted to active enzymes in a precise order
COMPLEMENT SYSTEM
• It works as a cascade system: when one reaction triggers another reaction which triggers others and so on; these types of systems can grow exponentially very fast
COMPLEMENT SYSTEM
o Following activation, opsonization occurs as complement components coat pathogenic organisms or immune complexes, facilitating the process of phagocytosis
- Opsonization
o Activation of the complement system results in induction of histamine release from mast cells and basophils, and stimulation of inflammatory response
- Inflammation
o In the final stage of the complement cascade membrane attack of target cells (e.g. bacteria and tumor cells) occur, leading to cell death
- Cytotoxic
Nomenclature:
1. ([?] for complement, [?] for the components)
2. The peptide chains
3. Cleaved peptides
4. If further proteolysis results in the loss of fragment activity
5. When a complement protein acquires enzymatic activity
“C”, 1 to 9
Greek letters (e.g. C3-α, C4-β)
lower case Arabic letters (e.g. C3a)
subscript “i”
horizontal bar
• Complement components are serum proteins produced by the __________ EXCEPT:
o ____________________________________________________
o ____________________________________________________
• Present in HIGHEST concentration in plasma: _____
• Key component of the pathways: _____
o Involves a more recently evolved mechanism of specific adaptive immunity
Classical Pathway
o It is initiated by the presence of antigen-antibody complex (immune complex)
Classical Pathway
o Classical pathway normally requires suitable antibodies bound to an antigen, complement components 1, 4, 2 and 3, and calcium (Ca++) and magnesium (Mg++) cations
Classical Pathway
Binds to Fc of IgM and IgG
C1q
Activates C1s
C1r
Cleaves C4 and C2
C1s
Part of C3 convertase
C4
Binds to C4b
C2
Key intermediate in all pathways
C3
Initiates membrane attack complex (MAC)
C5
Binds C5b in MAC
C6
Binds to C5bC6 in MAC
C7
Starts pore formation on membrane
C8
Polymerizes to cause cell
C9
It requires the interaction of all nine (9) major complement components
Classical Pathway
• A trimolecular complex (C1q, C1r, and C1s) held together by Ca+2 ions
C1: Recognition Unit
• C1q is the largest and consists of 6 globes held on slender shafts that fuse a common base
C1: Recognition Unit
o The 6 globes act as the recognition units that bind to the Fc region of IgM and IgG
C1: Recognition Unit
• For C1q to initiate the cascade, it must attach to two Fc fragments from IgG and/or IgM
C1: Recognition Unit
attaches to the immunoglobulin and initiates complement activation
C1q
initiates C1r
C1q binding
cleaves C1s
C1r
• C4 is a beta globulin originates from a proC4 synthesized by the macrophage
C4: First activation unit
• It consists of 3 peptide chains (C4-α, C4-β, C4-γ) joined by disulfide bonds
C4: First activation unit
• C4 is cleaved into C4a and C4b by C1s
C4: First activation unit
mediates cleavage of C4 into C4a and C4b
C1s
is bound to cell membrane while C4a is released into the fluid phase
C4b
• C2 is cleaved into C2a and C2b by C1s in the presence of C4b
C2: Second activation unit
in the presence of C4b (C14b) cleaves C2 units into C2a and C2b
C1s
is bound to the cell-bound C4b while C2b is released in the fluid phase
C2a
• It is the most abundant complement component in the serum.
C3: Third activation unit
• It is cleaved by C3 convertase into C3a and C3b.
C3: Third activation unit
is cleaved by C3 convertase into C3a and C3b
C3
remains unbound C3b is bound to the cell bound C4b2a (C4b2a3b: _______________)
C3a
• C5 is cleaved by C5 convertase into C5a and C5b
C5: First membrane attack unit
is cleaved by C5 convertase into a smaller C5a and a larger C5b
C5
is released into the surrounding fluid medium
C5a
is the first component of the membrane attack complex. It is the receptor of C6 and C7
C5b
binds to C6 forming a stable C5b6 complex
C5b
: Second membrane attack unit
C6
: Third membrane attack unit
C7
binds to C7 forming the stable C5b67 that is bound to the target cell membrane
C5b6
: Final membrane attack unit
C8
binds to C5b67 complex and leakage of membrane begins.
C8
Cell lysis can occur by the C5b678 complex in the absence of
C9
: Final membrane attack unit
C9
binds to C5b678 complex and accelerates cytolysis by producing circular lesions in the membrane
C9
induces the formation of hollow cylinders (tubules) in the bilipid layer of the cell membrane allowing exit of electrolytes and water out of the cell
C5b6789 complex
o Provides nonspecific innate immunity
Alternate Pathway
o It is considered a primitive defense mechanism, a bypass mechanism that does not require C1, C4 and C2 interaction
Alternate Pathway
o An antigen-antibody complex is not required for it to take place
Alternate Pathway
Binds C3b to form C3 convertase
Factor B
Cleaves Factor B
Factor D
Stabilizes C3 convertase
Properdin
Begins with the activation of C3 and requires Factors B and D, and magnesium cation (Mg++), all present in normal serum
Alternate Pathway
The initial recognition necessary for the alternative pathway is the presence of C3, specifically (?) which is probably continuously generated in small amounts in the circulation
C3b
C3 activation: o Non-immunologic
• Lipopolysaccharide (LPS)
• Endotoxin from the cell walls of gram-negative bacteria
• Cell walls of some bacteria
• Cell walls of yeasts (zymosan)
• Cobra venom factor (CVF)
C3 activation: o Immunologic
• IgA
• Other antibodies
exists in trace amounts in normal serum
C3b
interacts with Factor B (C3 proactivator) to form C3bB, which is a magnesium ion-dependent complex
C3b
is cleaved by Factor D (C3 proactivator convertase) into 2 fragments, Ba and Bb Ba is released and Bb is bound to C3b forming the C3bBb complex: amplification C3 convertase
C3bB
When stabilized by (?), the C3bBb complex becomes the C3 convertase that cleaves C3 into C3a and C3b
Properdin (P)
As more (?) is generated, the complex expands (C3bnBb) and becomes a C5 convertase
C3b
cleaves C5 into C5a and C5b initiating the membrane attack pathway
C5 convertase
Membrane attack complex
(C5b6789)
• Involved attachment of mannose-binding lectin to mannose residues on glycoproteins or carbohydrates on surface of microorganisms
Mannose-Binding Lectin (MBL) Pathway
Binds to mannose
Mannose Binding Lectin (MBL)
Helps cleave C4 and C2
MBL-associated Serine Protease-1 (MASP-1)
Cleaves C4 and C2
MBL-associated Serine Protease-2 (MASP-2)
Macrophages that digest microbes release chemicals that cause the liver to produce (?): proteins bind to carbohydrates on the microbe surface
lectins
is produced by liver in acute phase inflammatory reactions
MBL
binds to mannose on many bacterial cells
MBL (mannose-binding lectin)
Once MBL binds to target cell, (?) bind to bacterial surface Acts like C1
2 serine proteases (MASP-1, MASP-2)
Cleaving of C4 and C2 forming
C3 convertase
Cleaving C3 forming
C5 convertase
Cleaving of C5 initiates the formation of the
membrane attack complex (C5b6789)
are the key elements in a serologic reaction.
Antigens and antibodies
The study of the properties and types of antigens and antibodies are essential in the understanding of (?)as well as the (?) of the immune system.
serologic reactions ; responses
usually are present in humans as well as in animal serum. They may participate in serologic reactions, although some tests in serology, human complement is often inactivated, and an exogenous complement is used.
complement proteins
are activated in a cascade of reactions when these participate in a serologic reaction
complement proteins
The pathogens capable of causing infectious diseases in humans include bacteria, viruses, fungi, parasites and infectious proteins. (?) are usually associated with these pathogens.
Antigens
The J chain is found only in the following immunoglobulins
Activation Sequence: C1q attaches to the immunoglobulin and initiates complement activation ® C1q binding initiates C1r ® C1r cleaves C1s
C1: Recognition Unit
Activation Sequence: C1s mediates cleavage of C4 into C4a and C4b ® C4b is bound to cell membrane while C4a is released into the fluid phase
C4: First activation unit
Activation sequence: C1s in the presence of C4b (C14b) cleaves C2 units into C2a and
C2b ® C2a is bound to the cell-bound C4b while C2b is released in the fluid phase ® C4b2a complex is now attached on the surface of the cell membrane
C2: Second activation unit
Activation sequence: C3 is cleaved by C3 convertase into C3a and C3b ® C3a remains
unbound ® C3b is bound to the cell-bound C4b2a ® C4b2a3b complex is now attached on the surface of the cell membrane
C3: Third activation unit
Activation Sequence: C5 is cleaved by C5 convertase into a smaller C5a and a larger
C5b ® C5a is released into the surrounding fluid medium ® C5b is the first component of the membrane attack complex that is bound on the surface of the cell membrane that serves as the receptor of C6 and C7
C5: First membrane attack unit
Activation Sequence: C6 binds to cell-bound C5b forming a stable C5b6 complex
C6: Second membrane attack unit
Activation Sequence: C7 binds to cell-bound C5b6 forming the stable C5b67 that is bound to the target cell membrane
C7: Third membrane attack unit
Activation Sequence: C8 binds to C5b67 complex and leakage of membrane begins ® Cell lysis can occur by the C5b678 complex in the absence of
C8: Final membrane attack unit
Activation Sequence: C9 binds to cell-bound C5b678 complex accelerates cytolysis by
producing circular lesions in the membrane ® C5b6789 complex induces the formation of hollow cylinders (tubules) in the bilipid layer of the cell membrane allowing exit of electrolytes and water out of the cell
C9: Final membrane attack unit
where C3b that exists in trace amounts in normal serum becomes membrane bound on the surface of target cells
C3 activation
The membrane-bound (?) interacts with Factor B (C3 proactivator) to form C3bB, which is a magnesium ion-dependent complex
C3b
is cleaved by Factor D (C3 proactivator convertase) into 2 fragments, Ba and Bb
C3bB
is released, and Bb is bound to C3b forming the C3bBb complex: amplification C3 convertase
Ba
When stabilized by (?), the C3bBb complex becomes the C3 convertase that cleaves C3 into C3a and C3b
Properdin (Factor P)
As more (?) is generated, the complex expands (C3bnBb) and becomes a C5 convertase (e.g., C3bBb3b)
C3b
MBL acts like (?) of the classical pathway but binds to mannose on many bacterial cells
C1q
Once MBL binds to the target cell, (?) bind to the bacterial surface. MASP-1 and MASP-2 act like C1r and C1s of the classical pathway, respectively
two serine proteases (MASP-1, MASP-2)
