Huma immunity Flashcards
What are the types of light chain in an antibody?
→κ or λ chain
How many types of heavy chains?
→5
→μ,δ,γ,α or ε chain
What is the hinge region made from?
→disulphide bonds
→between the cystine groups
What Bcells have antibodies?
→activate Bcells- membrane bound
→plasma
Which regions make the antigen binding domain?
→variable region of H and L
What do all chains have at the beginning and end and why?
→NH3 at the beginning
→COO3 at the end
→chains are a string of amino acids
Where is the hinge region and why?
→between CH1 and CH2 for flexibility
What group is added to the antibody to allow interaction of immune cells?
→CHO glycosylation on CH2
Which fragments make the Fc fragment?
→CH2 and CH3 domain
Which fragments make the Fab fragment?
→variable and 1st constant domain
What is the function of Fab fragment?
→binds to antigens
→antigen-binding site
What is the function of the Fc region?
→interacts with Fc receptors on macrophages and some proteins of the complement system
→bear a highly conserved N-glycosylation site
What is the Fv region?
→the smallest fragment that maintains the full binding capacity of the intact antibody
What are hypervariable regions?
→3 of them
→on heavy and light chains
What are the functions of antibodies?
→Virus & toxin neutralization- prevents pathogen-host binding →Opsonization+ ADCP →Complement fixing/+ MAC formation (CDC)-Phagocytosis or lysis →Opsonization \+ ADCC leads to NK-induced apoptosis
What is ADCC and ADCP?
→ADCC: an excess of engaged CD16A induces the release of cytotoxic granules which kill the target
→ADCP: an excess of engaged CD32A induces the phagocytosis of the microbe or target cell
What gene region fixes light chain?
→VD-J
Describe IgM
→3rd most common →heaviest →fixes complement →does not cross placenta →pentameric
What is the function of IgM?
→Main Ab of primary response
→ best at forming immune complexes fixing complement;
→monomer serves as BCR
What are the functions of IgD?
→BCR;
→indicates mature B cells
→only Ab not secreted
What are the functions of IgG?
→Main Ab of secondary responses
→neutralize toxins;
→opsonization
What are the functions of IgA?
→Secreted into mucous, tears, saliva, colostrum
What are the functions of IgE?
→allergy
→parasite
Which Igs can cross the placenta?
→IgG
Which Igs fixes complement?
→IgM
→IgG
Which Igs is heaviest?
→IgM
How many types of IgG?
→1-4
How many types of IgA?
→2
Which Igs is involved in primary response?
→IgM
What joins the two IgA monomers?
→J chain
What is another structure found in IgA?
→secretory component
What is the only Ab not secreted?
→IgD
What are the major changes in heavy chain class switching?
→DNA recombination
→IgM to IgG, IgA, IgE
→IgG to IgA, IgE
What are the minor heavy chain changes in class switching?
→: Differential splicing (mRNA level)
→IgM and IgD
→Does not affect the DNA of Bcell itself
What does clas switching recombination require?
→Cytokine signal
→Switch regions- infront of constant gene segments constant
→AID and DSB repair proteins
What happens to the gene code after class switching occurs?
→other regions are removed
Before recombination what does the Bcell express?
→expresses gene in two forms: IgM and IgD
Compare secreted and membrane-bound Abs
secreted
→has cytoplasmic tail
→has a tail piece
membrane bound
→hydrophobic transmembrane region
→cytoplasmic tail
Which gene regions codes for transmembrane region of membrane bound Ab?
→M1 and M2
heavy chain
What is unique about transcription of membrane bound Ab?
→whole gene region is transcribed
What is involved in somatic recombination of Ab?
→V(D)J recombination
→Tdt nucleotide addition
→Somatic hypermutation
→Class switching
What molecules are involved in class switching recombination?
→AID
→DSB repair proteins
Which Ab do immature Bcells express?
→IgM
What are the gene changes that occur between pro-Bcell and mature Bcell?
→D to J, heavy chain variable region
→V to DJ
→V to J, light chain variable and constant
Where in the antibody does affinity chain maturation occur?
→heavy chain constant region
What is IgD considered as?
→quality control
How many Abs genes are inherited?
→none
→only gene segments
Compare the gene segments of light and heavy chain
→heavy chain has D region but light chain doesn’t
What do J or D/J region code for?
→Codes for CDR3
→Most variable region of Ab
What are the genetic loci encoding Ig?
→Two for light chain: kappa (κ)- chromosome 2
→lambda (λ) locus- chromosome 22
→One for heavy chain- chromosome 14
How many variable region segments does the kappa light have on chromosome 2?
→40
How many joining segments does kappa light chain have?
→5
Describe the proximity of V and J and C regions in germline DNA
→J segments far from V segment
→J segments closer to C segment than V segment
How many variable segments present on gamma heavy chain genes?
→51
How many D segments on gamma heavy chain?
→27
How many J segments on gamma heavy chain genes?
→6
What are RSS?
→recombination signal sequences
→conserved sequences upstream or downstream of gene segments
What is the function of RSSs?
→Turns’ consisting heptamer and nonamer with a 12 or 23 bp spacer
→Recombination only occurs between a segment with a 12bp
spacer and a 23bp spacer
→One turn two turn rule prevents V fragments and V/J fragments from combining
What factors are involved in the generation of antibody diversity?
→Multiple germline V, D and J gene segments
→Combination V-J and V-D-J joining
→Junctional flexibility
→ P-nucleotide addition
→ N-nucleotide addition
→ Combinatorial association of heavy and light chains
→ Somatic hypermutation during affinity maturation
What is a disadvantage of junctional diversity?
→incorrect reading frame –
wasteful process eg loss of stop codon
What is the difference between minor and major hairpin?
→Major hairpin=hole DNA folded in half
→Minor hairpin=between two strands of DNA
What is Artemis?
→endonuclease
→resolution of hairpin coding ends
Describe the junctional diversity process
→Once hairpin is formed, the Artemis enzyme nicks on end of the dsDNA
→Nicked ends linearise
→Repair enzymes adds nucleotides P nucleotides
→Tdt adds N nucleotides before the ends are ligated
→P and N nucleotides shifts reading frame
Which chain does Tdt mostly work on?
→heavy chain
How is Ab allele expression different from normal expression?
→Two copies of each Ig gene – one from mother and one from father
→ In other cells, both genes are expressed
→Only one heavy chain allele and one light chain allele is expressed
State the order of rearrangement in antibody rearrangement
→Heavy>kappa>lambda; 1st allele then 2nd
→Ensure each B cell makes one type of antibody
Where does class switching occur?
→spleen
→lymph node
→light zone
What are the two types of Bcell activation?
→Tcell independent
→Tcell independent
Describe Tcell independent Bcell activation
→production of IgM by plasma cells and
→does not produce memory B cells
→clonal expansion
Describe Tcell dependent activation
→BCR recognise antigen
→Th cell MHC: TCR and CD40 interaction
→cytokines
What does SyK do?
→phosphorylates signal molecule for Bcell activation
Describe affinity maturation
→Initially, the antibody binds weakly- low affinity so antigen takes longer to bind to antigen or quickly falls away
→When Bcell is activated, there is mutations in variable region genes and selects for antibodies with best affinity
→occurs in germline centre
Which is the only cell that can enter germline centres?
→T follicular helper cells (Tfh)
Which cells present antigens in the germline centre?
→Follicular Dendritic Cells (FDC)
Where do activated Bcells go to make clones?
→germline centre
What changes occur before Bcells turn into plasma or Bcells?
→class switching
What is the role of AID?
→generate point mutation in variable region- somatic hypermutation in dark zones
What do Bcells compete for in the light zone?
→compete to bind on the FDC and present it to Tfh cells
→Bcells then return to dark zones until affinity is high enough.
→Cells that don’t survive undergo apoptosis
