L4: AR - B cells and Antibody

what is the role of b cells in adaptive immunity

to recognise specific antigens and produce antibodies

what is clonal selection theory

each b cells has one specific receptor - when it binds, its antigen proliferates and produces identical cells

why is diversity of receptors important

to recognise a huge range of different pathogens

what is an antigen

a molecule recognised by immune receptors (BCR/TCR)

is antigen binding covalent or non covalent

non-covalent (reversible)

what forces are involved in antigen binding

• hydrogen bonds

• electrostatic

• hydrophobic

• van der waals

what is the basic structure of an antibody

2 heavy chains

2 light chains

what types of light chains exist

Kappa (k) and lambda (y)

what regions do antibody chains have

variable and constant

which region binds antigens

variable region

what determines antibody specificity

amino acid sequence in variable region

what is BCR

membrane bound antibody on b cells

which antibodies are expressed on naive b cells

IgM and IgD

what is special about IgM structure

monomer when membrane-bound, pentamer when secreted

what molecules help BCR signal inside the cell

Iga and Igb

why can different b cells recognise different antigens

variable regions differ in amino acid sequence

how many antigens can one b cell recognise

one specific antigen

what is V(D)J recombination

process that generates antibody diversity by rearranging gene segments - variable, diversity and joining segment

do light chains have D segments

no, only V and J

when does VDJ recombination occur

during b cell development in bone marrow

which enzymes mediate VDJ recombination

RAG1 and RAG2

what sequences do RAG enzymes recognise

RSS - recobination signal sequences

how does VDJ recombination generate diversity

random selection of VDJ segments

what increases diversity at junctions

imprecise joining (deletions and additions)

which enzymes add nucleotides randomly

TdT (terminal deoxynucleotidyl transferase

what happens if recombination is defective

severe combined immunodeficiency (SCID)

what are CDRs

regions in antibody variable domain that bind antigen

how many CDRs per chain

3

which CDR is most variable

CDR3

what is somatic hypermutation

mutation of antibody gene after exposure to improve binding

where does somatic hypermutation occur

germinal centre

which enzyme is involved in SH

AID (activation-induced deaminase)

what is the result of somatic hypermutation

increased antibody affinity (affinity maturation)

what happens after antigen binds BCR

signal transduction → b cell activation

what do activated b cells become

plasma cells (antibody secretion) or memory B cells