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
