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Questions and Answers
What are antibodies primarily composed of?
Which type of light chain is found in immunoglobulins?
T cell dependent activation of B cells primarily occurs with which type of antigen?
What is the Fab fragment of an antibody composed of?
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Which of the following statements is true regarding T cell independent activation?
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What constitutes the basic unit of an immunoglobulin?
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Which heavy chain type is NOT found in antibodies?
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How are the heavy and light chains of antibodies connected?
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What is the major immunoglobulin present in serum, constituting 75% of serum immunoglobulin?
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Which immunoglobulin class is primarily involved in the primary immune response?
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Which feature distinguishes IgG from IgM?
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What structural form does IgA take when found in secretions?
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What role do Fc regions of immunoglobulins play?
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Which immunoglobulin class is associated with anti-parasitic activity?
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Which immunoglobulin class is known for its agglutinating properties?
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What percentage of serum immunoglobulin does IgA normally constitute?
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What protects secretory IgA from digestive enzymes?
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Which immunoglobulin is primarily involved in Type I hypersensitivity?
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What is the main type of antibody produced during the primary immune response?
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What characterizes the secondary immune response?
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How are monoclonal antibodies produced?
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What is the role of eosinophils in relation to IgE?
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Which immunoglobulin is generally found in low levels in serum and acts as an antigen receptor on B cells?
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What is the function of secretory IgA in mucosal immunity?
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Study Notes
Humoral Immunity (HI)
- Definition of Antibody: Glycoproteins found in serum and tissue fluids, binding specifically to the antigen that triggered their production.
- Humoral Immunity: Mediated by antibodies produced by B lymphocytes and secreted by plasma cells.
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B Cell Activation:
- T cell dependent activation: Antigen is protein-based, B cells act as antigen-presenting cells (APCs), requiring T lymphocytes for activation.
- T cell independent activation: Antigen is non-protein based, these molecules are not processed by APCs and do not activate helper T cells.
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Structure of Immunoglobulins:
- Basic unit (monomer): Four polypeptide chains – two light chains and two heavy chains.
- Light chains: Two antigen types: Kappa (K) and Lambda (A). Only one type found in an individual molecule.
- Heavy chains: Five types: Gamma (γ), Alpha (α), Mu (µ), Delta (δ), and Epsilon (ε).
- Disulfide Bonds: Connect between heavy and light chains, the two heavy chains, and within polypeptide chains.
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Variable (V) and Constant (C) Regions:
- Light chain: Variable (VL) and Constant (CL)
- Heavy chain: Variable(VH) and 3 Constant (CH)
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Hinge Region: Where the arms of the antibody molecule form a Y shape.
- Fab: Fragment containing antigen binding sites.
- Fc: Fragment containing the remainder of the two H chains (mediates effector functions).
Functions of Immunoglobulins
- Antigen Binding: Specific binding to antigens.
- Activation of Complement: Leads to cell lysis.
- Opsonization: Coating of organisms with antibodies, enhancing phagocytosis.
- Antibody-dependent Cellular Cytotoxicity (ADCC): Destruction of antibody-coated target cells by NK cells, macrophages, neutrophils, eosinophils.
Classes of Immunoglobulins
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IgG:
- Gamma heavy chains
- Structure: Monomeric unit
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Properties & Functions:
- Major serum immunoglobulin (75% of serum Ig).
- Major Ig in secondary immune response.
- Only Ig that crosses the placenta.
- Activates complement.
- Opsonization.
- Rh antibodies are IgG.
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IgM:
- Mu heavy chains
- Structure: Pentamer with a J chain (monomer on B lymphocytes as an antigen receptor).
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Properties & Functions:
- Third most common serum Ig (7% of serum Ig).
- Major Ig in primary immune response.
- Cannot cross the placenta.
- Activates complement.
- Good agglutinating Ig.
- Antibodies of ABO blood groups.
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IgA:
- Alpha heavy chains
- Structure: Serum IgA - monomer; Secretory IgA in secretions - dimer with a J chain and secretory piece.
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Properties & Functions:
- Second most common serum Ig (15% of serum Ig).
- Secretory IgA present in secretions (tears, saliva, colostrum, mucus), essential for mucosal immunity.
- Inhibits binding of pathogens to mucosal cells.
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IgD:
- Delta heavy chains
- Structure: Monomer
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Properties & Functions:
- Found in low levels in serum.
- Found on B cell surfaces as an antigen receptor.
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IgE:
- Epsilon heavy chains
- Structure: Monomer
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Properties & Functions:
- Least common serum Ig, binds tightly to Fc receptors on basophils and mast cells.
- Involved in Type I hypersensitivity reactions.
- Plays a role in parasitic infections.
- Eosinophils have Fc receptors for IgE, leading to killing of parasites through ADCC.
Primary Immune Response
- First exposure to a foreign antigen.
- Lag phase of 1-2 weeks for detectable antibody levels (mainly IgM).
- Antibody levels decline rapidly.
Secondary Immune Response
- Second exposure to the same antigen after primary immunity.
- Rapid and steep rise in antibody levels (mainly IgG) that persists for weeks or months.
- Due to the presence of immunological memory cells.
- Faster and stronger response than the primary response.
Monoclonal Antibodies
- Definition: Highly specific antibodies produced against a single epitope.
- Formation: Obtained by fusing a B cell producing antibodies against a single epitope with a myeloma cell (malignant plasma cell). The fused cell is called a hybridoma cell.
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Description
Test your knowledge on humoral immunity and antibodies in this quiz. Explore B cell activation processes, the structure of immunoglobulins, and their roles in the immune response. Perfect for students studying immunology!
