Lecture 6: B Cells and Antibodies Flashcards
draw an antibody with its heavy chains and light chains
check with fragment antigen binding site (FAB) and and fragment crystallisable region (Fc)
which chains are constant and which are variable
- heavy chain is constant
- light chain is variable
what is an epitope
a specific region on an antigen which interacts with an antigen binding site on an antibody. there are numerous epitopes on one antigen
on which region do antibodies attach to B cells
Fc region
how many types of antibody does each B cell produce?
just one, so all antibodies on the surface are he same
what are the different antibody isotopes
- IgM
- IgA
- IgD
- IgG
- IgE
IgM
- first antibody produced in immune response so present at birth
- has low affinity for antigens as it is immature
- forms pentamers which are held together by a joining chain (j chain)
IgA
- the only antibody that can cross mucosal surfaces
- found in secretions, but protected from digestion by secretory component (s chain)
- forms dimers with a joining chain (j chain)
- colostrum, a forerunner of breast milk is rich in IgA
IgD
like IgM is the first antibody produced by a B cell but has no known function
IgG
main mature antibody form, circulates as a monomer
IgE
- circulates as a monomer
- exact function not known but believed to be important in parasitic infection
- definitely important in allergies
describe neutralisation by antibody
- antitoxin antibodies bind to the toxin directly and neutralise it
- eg clostridium tetani releases a toxin that causes muscle contraction (tetanus)
describe receptor blocking by antibody
antibody binds to receptor on a virus so it can’t attch to host cell proteins
describe opsonisation
coating of bacteria by circulating antibodies to enhance phagocytosis
describe mast cell activation by antibodies
- mast cells found in the eye, skin, gut, lungs and nose
- have surface Fc receptors which get coated in IgE
- when the appropriate antigen binds to IgE and cross-links them, the mast cell “degranulates” releasing histamine
- inappropriately activated in allergy
describe antibody-dependent cellular cytotoxicity
natural killer cells have Fc receptors on their surface which recognise antibody coated bacteria and kill them by non-phagocytotic means
describe the complement response
- when an antibody interacts with an antigen it activates the complement system
- important for opsonisation, inflammation and terminal attack pathway
how are antibody receptors generated
somatic recombination
disadvantages of somatic recombination
- very energy intensive
- most receptors won’t be useful as they can’t fit biochemically or attack self antigens
- potential for autoimmune diseases as not all incorrect B cells can be destroyed properly
describe clonal selection
- we all start with a unique set of B cells, a small number of each B cell
- when exposed to an antigen, the B cell that responds to it is stimulated to divide and produce antibodies
describe class switch
when B cells divide in response to an antigen, IgM switches to IgG, so the variable region stays the same but heavy chain is swapped out
describe somatic hypermutation
- random mutations are introduced to the variable region of the antibody so daughter cells produce a slightly different antibody
- some may have higher or lower affinity to the antigens
- those with higher affinity go through clonal selection
- these B cells become long-lived memory cells
