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Questions and Answers
What defines the specificity of an antibody's immune response?
Which characteristic is true of the constant region of antibodies?
What is the function of the hinge region in antibodies?
Which statement regarding isotypes of antibodies is accurate?
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Which of the following best describes the variable region of an antibody?
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What type of antibody is produced after exposure to antigens or infections?
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What mechanism do antibodies use to facilitate the destruction of infected cells?
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Which type of antibody is produced to protect the organism's own species?
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What does the term 'agglutination' refer to in immunology?
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Which class of antibodies is specifically responsible for coating antigens to enhance phagocytosis?
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What is the primary characteristic of precipitins?
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Which of the following is TRUE about lysins?
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Which two types define the light chain in antibodies?
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What is a characteristic feature of complete antibodies?
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Which of the following is NOT true about the heavy chain of an antibody?
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What function does the Fab (Antigen binding fragment) perform?
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Which statement is correct regarding incomplete antibodies?
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What is the role of blocking inhibitory antibodies?
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In terms of antibody structure, which chain is responsible for stability?
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Which type of antibody has a univalent nature?
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What helps to bind the antigen to the antibody?
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Which antibody type has a hinge region?
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What is the result of papain digestion on antibodies?
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In the antibody classification, which type is associated with the epsilon heavy chain?
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What does IgG4 possess that is unique compared to other IgG subclasses?
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Which type of antibody is formed from the mu heavy chain?
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In terms of genetic polymorphisms, what do allotypes represent?
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According to Ehrlich's side chain theory, what happens to specific cells when exposed to antigens?
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What is true regarding IgM and IgE with respect to hinge regions?
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What is the primary role of IgA in the immune response?
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Which class of antibody is known for being the predominant immunoglobulin in humans?
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What is the half-life of IgA?
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Which antibody class participates in agglutination and precipitation reactions?
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Which subclass of IgA is mainly found in serum?
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What is a unique feature of IgM compared to other immunoglobulins?
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Which of the following statements about IgG is true?
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How does repeated exposure to an antigen affect lymphocyte populations?
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Study Notes
Immune Functions
- Neutralize toxic substances
- Facilitate phagocytosis and kill microbes
- Combine with antigens on cellular surfaces and cause destruction of these cells
Antibody Classes
- Acquired antibodies are produced by B cells after exposure to antigens or infections.
- Natural antibodies are present at birth and naturally occurring.
- Isoantibodies are produced to protect the organism itself.
- Heterophile antibodies are produced for other species.
Antibody Classification Based on Reaction with Antigen
- Agglutinins and Agglutinoids: Antibodies that cause agglutination when an antigen is bound to a cell (ex: blood typing).
- Precipitins: Antibodies that form a precipitate when they bind to a soluble antigen.
Antibody Classification Based on Sedimentation
- Hemagglutinins: Antibodies that cause the clumping of red blood cells.
- Lysins: Antibodies that cause lysis (bursting) of cells.
- Opsonins: Antibodies that coat antigens, making them easier for phagocytes to engulf.
- Neutralizing antibodies: Antibodies that bind to and neutralize toxins.
- Allergic antibodies: Antibodies that trigger allergic reactions by binding to antigens and releasing histamine and heparin.
- Antitoxins: Antibodies that neutralize toxins (same as neutralizing antibodies).
- Complement fixing antibodies: Antibodies that activate the complement pathway.
- Blocking of inhibitory antibodies: Antibodies that block the action of other molecules.
Antibody Structure
- Antibody is a tetrapeptide molecule with four chains: two heavy chains and two light chains.
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Heavy chain:
- Five principal antigenic types (gamma, alpha, mu, delta, epsilon)
- Determines the antibody's class and effector functions.
- Has three constant domains and one variable domain.
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Light chain:
- Two main types: kappa and lambda (not both present in the same antibody).
- Two domains: one constant and one variable domain.
- The variable region of the light chain, together with the variable region of the heavy chain, forms the antigen-binding site.
- Disulfide bonds: Bind the heavy and light chains together.
- Antigen-binding site: Location where antigens bind to the antibody.
Antibody Regions
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Variable region:
- Located at the amino terminal end (NH2).
- Amino acid sequence varies and is responsible for antigen specificity.
- Contains unique antigenic determinants (idiotypes).
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Constant region:
- Located at the carboxyl terminal end (COOH).
- Amino acid sequence is fixed and unchanging.
- Involved in binding to host tissues.
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Hinge region:
- Flexible region located in the heavy chains between the CH1 and CH2 regions.
- Allows for flexibility in antigen binding.
- Papain acts here to produce Fab and Fc portions.
- Determines the half-life of the antibody.
Isotype
- Refers to the class of antibodies, which is defined by the constant region of the heavy chains.
- Examples: IgG, IgA, IgD.
- IgG, IgA, and IgD have hinge regions.
- IgM and IgE lack hinge regions.
Allotype
- Small differences in the constant regions of the heavy or light chains within a species.
- These variations do not affect the overall function of the antibody class.
- Important in transplantation and blood transfusions.
Antibody Digestion
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Pepsin:
- Cuts the antibody below the hinge region.
- Produces two fragments: one Fab and one small Fc prime fragment.
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Papain:
- Cuts the antibody above the hinge region.
- Produces three fragments: two Fab fragments and one whole Fc fragment.
Theories of Antibody Production
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Ehrlich's Side Chain Theory:
- Cells have specific surface receptors for antigens that are present before exposure to the antigen.
- The immune system selects cells with the proper receptors, the combination takes place, and receptors are released as antibody molecules.
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Clonal Selection Theory:
- Each lymphocyte is genetically programmed to produce one specific type of immunoglobulin.
- The immune system selects lymphocytes capable of responding to a specific antigen, causing them to proliferate.
- Repeated exposure to the antigen increases the pool of lymphocytes producing antibodies against that specific antigen.
Classes of Antibody
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IgG:
- Smallest monomer (1).
- Predominant immunoglobulin in humans (75% to 80% of total Ig).
- Longest lifespan of 23 to 25 days.
- Functions: provides immunity for newborns (crosses the placenta), starts complement pathway, coats antigens for phagocytosis, neutralizes toxins and viruses, participates in agglutination and precipitation.
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IgA:
- Dimer (2).
- Synthesized at a greater rate than IgG.
- Synthesized in plasma cells found in mucosal-associated lymphoid tissue (MALT).
- Half-life: 6 days.
- Cannot start complement pathway.
- Functions: patrols and guards mucosal surfaces, prevents adherence of organisms on mucosal surfaces, protects the infant digestive tract, acts as the first line of defense, neutralizes toxins.
- Two subclasses: IgA1 (mainly found in serum) and IgA2 (usually found in mucus membranes and surfaces).
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IgM:
- Pentamer (5).
- Star-shaped when free.
- Half-life is 10 days (6 days).
- Functions: starts complement pathway, activates B cells, participates in agglutination, neutralization, and precipitation reactions.
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Description
This quiz explores the diverse functions of the immune system and the classification of antibodies. Learn about acquired, natural, isoantibodies, and various types of antibody actions. Test your knowledge on how these antibodies interact with antigens and their roles in immune response.
