ch 17 pt 2

• Antibodies can activate complement (IgG and IgM)
• Antibodies bind to and neutralize a bacterial toxin
• Antibodies coat the pathogen (opsonization) which promotes phagocytosis
• The ultimate goal for antibodies it to target pathogens and their products for elimination by phagocytes
• antibodies are the secreted form of the BCR and are specific
• antibodies consists of:

  • 2 identical light chains
  • 2 identical heavy chains

  
• in an antibody, each light chain is joined to a heavy chain by a disulfide bond and noncovalent linkages
• each light chain/heavy chain dimer is joined to a light chain/heavy chain dimer by disulfide bonds
• Each light chain contains one variable region and one constant region (of one domain)
• Each heavy chain contains one variable reigon and one constant region (of 3 or 4 domains)
• Fab fragment: fragment antigen binding

  • composed of the light chain
  • part of the heavy chain

  
• Fc fragment: fragment crystalizable

  • portion of the constant region of the heavy chain

  
• Antibodies (immunoglobulins) are the secreted form of the B-cell receptor and are specific for one antigen binding site (epitope)
• Epitope: antigenic determinant

  • portion of an antigenic molecules
  • bound by an antibody

  
• One B cell and its clones will produce many antibody molecules
• Monoconal: all antibody molecules from a B cell and its clones will have the same specificity for their own epitope
• Polyclonal response: the generation of multiple monoclonal antibodies with unique epitopes generated to a particular antigen
• CDRs: complementary determining regions

  • hypervariable regions flanked by framework regions
• Antibodies are the secreted form of the BCR and are specific

  
• The six hypervariable regions of heavy chain and light chain form the antigen binding site
• one V segment and one J segment are joined to synthesize the variable region in a light chain.
• one v segment, one d segment, and one J segment are joined to synthesize the variable region in a heavy chain
• Junctional diversity: addition of new and random nucleotides at the V and J segments of light chain and D and J segments of heavy chain
• In the bone marrow, the heavy chain of a B cell is generated in 3 steps

  • somatic recombination
  • junctional diversity
  • addition of u constant region
• combinatorial diversity: different light chains combine the already generated heavy chain
• B-cells that do not encounter antigen will undergo apoptosis
• The five classes of antibodies on the constant region of their heavy chain

  
• Before leaving the bone marrow, B-cells undergo a selection process so they do not have a strong recognition of self
• Clones of mature B-cells are synthesized and released from the bone marrow have one antigen specificity and express IgM receptors
• The first class of antibodies produced during an infection are IgM antibodies
• Class switching takes place in lymph nodes following B cell activation with help from T cells
• B-cells that depart the bone marrow circulate between blood and lymph
• B-cells that encounter and phagocytose an antigen are activated
• In order for a B-cell to secrete antibodies, it needs the assistance of a T-cell in the lymph node
• A B-cell will phagocytose the antigen and present pieces of it to a helper T-cell in the context of an MHC molecule
• Not all activated B-cells will secrete IgM antibodies, some will migrate deeper into a lymph node and form a germinal center
• The germinal center (GC) is a specialized microstructure that forms in secondary lymphoid tissues
• B-cells that enter the germinal center of a lymph node undergo somatic hypermutation with the intention to generate antibodies of higher affinity for the antigen
• B-cells that display higher affinity are selected for and undergo class switching with the help of a helper t-cell
• Through class switching, some B-cells become plasma cells, while others become memory cells