Antibody Structure and Function

• What happens to B cells when they are stimulated by an antigen?

  B cells undergo differentiation and produce antibodies.
• What is another name for antibodies?

  Immunoglobulins.
• What is the early name for antibodies?

  Gamma globulin.
• What is the composition of antibodies?

  86-98% polypeptide and 2-14% carbohydrates.
• What percentage of plasma protein do antibodies constitute?

  At least 20%.
• Why is serum used in serology?

  Because it is where the antibody resides.
• What are the properties of antibodies?

  • Protein in nature (glycoprotein)
  • High molecular weight
  • Present in serum/plasma, saliva, semen, CSF, and other body fluids
• What are the classifications of immunoglobulins according to sedimentation constant?


  • IgG: 7s, 150,000 Da
  • Serum IgA: 7s, 160,000 Da
  • Secretory IgA: 9s; 11s; 13s, 170,000 Da
  • IgM: 19s, 900,000 Da
  • IgD: 7s, 180,000 Da
  • IgE: 8s, 190,000 Da
• What does the Svedberg Unit (s) indicate?

  It indicates sedimentation rate in analytical ultracentrifuge.
• What is the largest antibody?

  IgM.
• What is the molecular weight of IgM?

  900,000 Da.
• How many monomers does IgM have?

  Five monomers.
• What is the typical shape of an antibody?

  1. shaped (monomer).
• How do antibodies react according to temperature?

  • Cold antibodies: IgM (react in cold environment)
  • Warm antibodies: IgG (react at 37 degrees Celsius)
• What are the two types of antibodies according to occurrence?


  • Natural antibodies: Normally produced by the body
  • Immune antibodies: Produced in response to a particular antigen
• What are isoantibodies and heterophile antibodies?

  • Isoantibodies: From the same species
  • Heterophile antibodies: From other species
• What is the structure of immunoglobulin made up of?

  • Four chain tetrapeptides
  • Two heavy chains and two light chains
• What are the principal antigenic types of heavy chains?

  IgG = gamma, IgA = alpha, IgM = mu, IgD = delta, IgE = epsilon.
• What are the two antigenically defined types of light chains?

  Kappa and lambda.
• Who discovered Bence-Jones Protein?

  Dr. Henry Bence Jones.
• What happens to Bence-Jones Protein when heated at 60°C?

  It precipitates in the urine.
• What is the hinge region of an antibody?

  A flexible part located in the heavy chains.
• What accounts for the flexibility of the antibody?

  Proline content.
• Which chains contain the hinge region?

  Gamma, alpha, and delta chains.
• What is the role of carbohydrates in immunoglobulins?

  • Increase solubility of immunoglobulin
  • Provide protection against degradation
  • Enhance functional activity of the Fc domains
• What are the two types of disulfide bonds in antibodies?

  Interchain and intrachain.
• What are the domains in an antibody molecule?

  • Globular regions on polypeptide chain
  • Stabilized by intrachain disulfide bonds
  • A typical antibody has 12 domains
• How many light chains are in a typical antibody?

  Two light chains.
• How many heavy chains are in a typical antibody?

  Two heavy chains.
• What are the regions on the polypeptide chain of antibodies?

  • Variable region: changes amino acid sequence, binds to antigen
  • Constant region: fixed amino acid sequence, binds to host tissue
• What is a polymer in the context of immunoglobulins?

  Ig composed of more than a single basic monomeric unit.
• What is the J chain in immunoglobulins?

  A polypeptide chain that holds polymeric Ig.
• What is the secretory component in immunoglobulins?

  A substance attached to polymeric Ig found on secretions.
• What does papain enzyme do to IgG?

  It cleaves IgG into 2 Fab and 1 Fc.
• What does pepsin enzyme do to antibodies?

  It cuts antibodies after the hinge region forming F(ab)2 and 1 Fc.
• What is immunoglobulin variability?

  • Variability means variation or differences of the antibody
  • Isotypic variation: Same heavy chain for each class
  • Allotypic variation: Variations in constant regions
  • Idiotypic variation: Variations in variable regions
• What are the characteristics of Immunoglobulin G (IgG)?

  • Codes for gamma chain
  • Predominant immunoglobulin in humans (70-75%)
  • Longest half-life (23 days)
  • Appears later than IgM in primary response
  • Major antibody of secondary immune response
  • Maternal IgG transfers across the placenta
• What are the major functions of IgG?

  • Provides immunity in newborns
  • Fixing complement
  • Coating antigen for enhanced phagocytosis
  • Neutralizing toxins and viruses
  • Participating in agglutination and precipitation reactions
• What are the functions of IgM?

  • Complement fixation
  • Agglutination
  • Opsonization
  • Toxin neutralization
  • Defense against bacterial diseases
• What are the characteristics of Immunoglobulin A (IgA)?

  • Represents 10-15% of all immunoglobulins
  • Found in mucosal areas, such as saliva and tears
  • Plays a crucial role in mucosal immunity