Humoral immunity

• What is the primary function of the humoral branch of the immune system?

  It involves the interaction of B cells with antigens and their differentiation into antibody-secreting plasma cells.

  
• What role do antibodies play in the humoral immune response?

  Antibodies function as the effector molecules of the humoral response.

  
• From where do B lymphocytes derive their designation?

  From their site of maturation in the bursa of Fabricius in birds.

  
• Where do B lymphocytes mature in most mammalian species?

  In the bone marrow.

  
• What are the membrane-bound immunoglobulins expressed on mature B cells?

  IgM and IgD.

  
• What is the function of Class II MHC molecules on B cells?

  They allow B cells to function as antigen-presenting cells (APCs).

  
• What are CR1 and CR2 receptors on B cells for?

  They are receptors for certain complement products.

  
• What is the role of CD40 in B cell activation?

  CD40 interacts with CD40 ligand on helper T cells, which is critical for the survival and development of B cells.

  
• What are the two types of B cell activation processes?

  Cross-linkage-dependent B-cell activation and cognate help.

  
• What is required for cross-linkage-dependent B-cell activation?

  Antigens with repetitive epitopes.

  
• What is cognate help in B cell activation?

  It provides co-stimulatory signals that rescue B cells from inactivation.

  
• How do receptor cross-linkage stimuli and cognate help work together?

  They synergize to yield more vigorous B-cell responses.

  
• What are the two outcomes of B cell activation?

  They can differentiate into antibody-secreting cells or memory cells.

  
• What are the components of an antibody molecule?

  Two identical heavy chains and two identical light chains.

  
• What is the significance of the variable regions in antibody chains?

  They contain hypervariable regions that bind to specific antigens.

  
• How many major classes of immunoglobulins are there?

  Five major classes: IgG, IgA, IgM, IgD, and IgE.

  
• What determines the class and subclass of an antibody molecule?

  The heavy chains' antigenic and structural properties.

  
• What types of light chains can be found in antibodies?

  Kappa (κ) and lambda (λ) chains.

  
• What is the composition of IgM in terms of its structure?

  IgM is a pentamer with 10 antigen-binding sites.

  
• What is the primary role of IgM in the immune response?

  It is the first immunoglobulin class produced in response to an antigen.

  
• How does IgM contribute to complement activation?

  IgM is more efficient at activating complement compared to other isotypes.
• What is the role of the J chain in IgM?

  It allows IgM to bind to receptors on secretory cells for transport across epithelial linings.

  
• What is the major isotype found in secretions?

  IgA.
• How does serum IgA differ from secretory IgA?

  Serum IgA is a monomer, while secretory IgA is a dimer stabilized by J chains.

  
• What are the two subclasses of IgA in humans?

  IgA1 and IgA2.

  
• What is the primary function of IgA in mucosal immunity?

  It acts as an important component of the first line of defense against organisms entering through mucosal routes.

  
• What is the role of IgA1 in serum?

  IgA1 has an extended hinge that allows it to bind antigens at various spacings.

  
• How does IgA protect against pathogens?

  By binding and cross-linking pathogens.

  
• What is the least abundant immunoglobulin?

  IgE.

  
• What is the primary role of IgE in the immune system?

  It is involved in the clearance of parasites and allergic responses.

  
• What is the most abundant immunoglobulin in the blood?

  IgG.

  
• How many subclasses of IgG are there?

  Four subclasses: IgG1, IgG2, IgG3, and IgG4.

  
• Which IgG subclasses can cross the placenta?

  IgG1, IgG3, and IgG4 can cross the placenta.

  
• Which IgG subclass is the most effective complement activator?

  IgG3 is the most effective complement activator.

  
• What is the role of IgD in B cells?

  IgD is a major membrane-bound immunoglobulin expressed by mature B cells, but its biological function is under investigation.

  
• What are polyclonal antibodies?

  They are a heterogeneous mixture of antibodies directed against various epitopes of the same antigen.

  
• How are monoclonal antibodies different from polyclonal antibodies?

  Monoclonal antibodies are a homogeneous population directed against a single epitope, while polyclonal antibodies are directed against multiple epitopes.

  
• Why are polyclonal antibodies typically more robust than monoclonal antibodies?

  Because they can recognize multiple epitopes on a single molecule.

  
• What is the difference between primary and secondary antibody responses?

  Primary responses result from naive B cell activation, while secondary responses are due to memory B cell stimulation.

  
• What happens to heavy chain isotype switching and affinity maturation with repeated exposure to protein antigens?

  They increase with repeated exposure.