B cells Flashcards
What is the antibody (immunoglobulin) structure made of?
4 polypeptide - two identical heavy chains (H) and two identical light chains (L) each containing a variable and constant region
What is Fab?
fragment, antigen-binding region
What is Fc?
fragment, crystalline
What are the 5 isotypes of antibodies?
IgM, IgD, IgG, IgA, IgE
What are the Fc receptors for IgG?
FcγR
What are the Fc receptors for IgE?
FcεR
What are the Fc receptors for IgA?
FcαR
What are the Fc receptors for IgM?
FcμR
What antibody class is predominant in blood?
IgG and IgM
What are major antibodies in extracellular fluid?
IgG and IgA
What antibody is usually predominant in secretions across epithelia?
IgA
What antibody is usually provided to the foetus by the mother?
IgG
What antibody is associated with mast cells just beneath epithelial surfaces?
IgE
What is the function of IgA?
protect epithelial surfaces from infectious agents
What do IgM and IgG activatye?
classical complement pathway
What do Fcγ receptors facilitate?
phagocytosis of antibody-bound cells
The main functions of all antibodies is?
- neutralisation
- opsonisation
- antibody dependent cellular cytotoxicity (ADCC)
- complement activation
What makes up the B cell receptor (BCR)?
membrane bound immunoglobulin (IgM/IgD) with unique specificity
surface single antibody molecule (Igα or Igβ)
What are the distinct roles in B cell activation?
performs first signal of activation - binding to cognate antigen
internalise antigen (APC function) to present MHC class II molecules
What is an immunoreceptor tyrosine-based activation motif?
highly conserved region in the cytoplasmic domain
activated when receptors are ligated and produces an intracellular signal
What are P nucleotides?
inserted nucleotides as a result of imprecise joining during V(D)J recombination
What are N nucleotides?
are random nucleotides inserted at each VDJ joint by the enzyme terminal deoxynucleotidyl transferase (TdT)
What increases diversity of B cell receptor?
N and P nucleotides
What are the two types of B cell activation?
non protein antigens without T cell help
protein antigens require T cell help
What antibodies are mostly produced by non protein antigen activating B cells?
IgM
What antibodies are typically produced from protein antigens requiring T cell help?
antibodies with isotype switching and high affinity
What are characteristics of T-independent B cell activation?
antigens are multivalent
response = fast
short-lived plasma cells
What are characteristics of a T-dependent B cell activation?
antigen = protein component
two received signals
response = slower
memory B cells and long-lived plasma cells
What are the two responses B cell receives during T-dependent activation?`
- through antigen receptor
- CD4+ T helper cell interaction (recognition of same antigens)
What are the two responses B cell receives during T-dependent activation?`
- through antigen receptor
- CD4+ T helper cell interaction (recognition of same antigens)
What can activated B cells act as?
professional APCs
What is linked recognition?
see same parts of the same antigen
but B cells see it as naive
and T cells = “chopped up”
What interaction is important between B cells and T cells?
CD40 and CD40 ligand on T cell
What is affinity maturation?
process by which the affinity of antibodies produced in response to a protein antigen increases with prolonged or repeated exposure to that antigen
What causes affinity maturation?
point mutations in V regions
