B Cell Activation, Affinity, Maturation & Class Switching Flashcards
When does a B cell become a mature B cell?
β When it is capable of making IgM and IgD
Once a mature circulating B cell encounters a pathogen what does it do?
β Migrated to the germinal center in the lymph node
Where does the mature B cell undergo affinity maturation and class switching?
β In the germinal center
What is the function of affinity maturation and class switching?
β Codes the heavy chain constant region of the B cell
What does affinity maturation do?
β further hones the variable fragment of the antibody to that particular pathogen
During affinity maturation what signals does the B cell receive and why?
β Receives signals from T cells about which pathogen the body is dealing with
β this is so it switches its heavy chain constant region to deal with the pathogen
What are the two things a B cell can differentiate into?
β Plasma cells
β Memory B cells
What is an antibody made up of?
β Two heavy chains and two light chains
What part of the antibody makes up the antigen binding variable fragment?
β The first domains of the light and heavy chain
What is the constant region of the antibody for?
β Biological effector functions
What is neutralisation and what does it do?
β Antibodies binding to the docking site of the virus
β It prevents the virus from entering the cells
β binds to the active site of toxins and neutralises the toxins
What is opsonisation used against and why?
β mostly bacteria because they are larger than viruses
How is opsonisation done?
β The antibody tags the surface of bacteria to recruit other cells such as macrophages
What happens once antibodies have opsonised a bacterium?
β The macrophage has Fc receptors on itβs membrane that bind to the CH2 region of the antibody
β The macrophage performs ADCP (antibody dependent cellular phagocytosis) for bacteria
How does opsonisation for tumor cells occur and what happens as a result of this?
β The antibody tags the tumor cell and recruits NK cells to perform ADCC (antibody dependent cellular cytotoxicity)
β NK cells produce chemicals to cause the tumor to apoptose because they are too large to be engulfed
What are the 4 functions of antibodies?
β Neutralisation
β Opsonisation
β Opsonisation for tumor cells
β Complement fixing
What are the two immune complexes formed by antibodies?
β A lot antibodies can bind to the surface of the bacteria and cause agglutination which gets cleared by macrophages
β complement molecules such as C1Q, C1s and c1r bind to the antibody and lead to phagocytosis and inflammation
What are the two ways complement fixing works?
β formation of MAC (membrane attack complexes) which punches holes in the tumor cells -lysing them
β antibodies can also form complexes with the complement (complement fixing) which leads to phagocytosis
How many classes of antibodies are there?
β 5
What determines antibody class?
β the difference in the heavy chain
What are 3 properties of IgG?
β 4 heavy chain domains
β stabilised by two disulfide bonds in between the heavy chains
What are disulfide bonds formed between?
β Two cysteine residues of amino acid
How is IgD different from IgG?
β it has a longer hinge that is stabilised by one disulfide bond
How many domains does IgE have?
β 5 domains
How is IgA different to IgG?
β similar but the third CH3 domain has a modification which allows interaction with the J chain so the two monomers can join together
β wrapped by secretory components to be secreted into the mucus
What is IgM similar to?
β IgD
How many domains does IgM have and how can it form a pentamer?
β 5 domains
β forms a pentamer with the help of the J chain
What is the function of IgM?
β Fixes complement
What is the heavy chain of IgM?
β Mu
What is the heavy chain of IgD?
β delta
What is the heavy chain of IgG?
β gamma
What is the heavy chain of IgA?
β alpha
What is the heavy chain of IgE?
β epsilon
Which Ig has the heaviest molecular weight and why?
β IgM
β it forms a pentamer