B and T Lymphocyte Receptor Diversity Flashcards
compare and contrast BCRs and antibodies
BCRs and antibodies have the exact same structure, but antibodies are secreted and released by B cells while BCRs are membrane-bound
how many polypeptide chains make up a BCR? what 2 categories do they fall into?
4; 2 light (L) chains and 2 heavy (H) chains
what does the antigen-binding region of a BCR consist of and what is it referred to as?
consists of both light and heavy chains and is referred to as Fab (fragment antigen-binding)
how many Fab regions are on each BCR?
2 Fab regions on each BCR
what does the non-antigen-binding region of a BCR consist of? what is it referred to as?
consists of heavy chain only, referred to as Fc (fragment crystallizable)
how many antigens can each BCR bind at once?
2
what must be done to ensure that BCRs can bind lots of different antigens?
generate diversity at Fab region
what are the 2 regions of the Light chains of BCRs?
variable (VL) region and constant (CL) regions
describe the variable regions of Light chains of BCRs
hyper-variable from one cell to another
describe the constant regions of Light chains of BCRs
have either lambda or kappa genes
what two regions does the heavy chain AT THE Fab REGION of a BCR have?
has a variable (VH) and a constant (CH) region
describe the variable region of the heavy chain at the Fab region of a BCR
hyper-variable from one cell to the next
describe the constant region of the heavy chain at the Fab region of a BCR
is consistent from one cell to the next within a response, will be one of 5 options
what do the 5 heavy chain constant region classes correspond to?
the type of antibody produced
what are the 5 heavy chain classes and what type of antibody do they produce?
- mu: IgM
- delta: IgD
- gamma: IgG
- alpha: IgA
- epsilon: IgE
how is immunoglobulin/BCR diversity generated in the variable regions or light and heavy chains? (2)
- gene recombination
2. gene conversion
describe gene recombination to generate diversity in the variable regions of BCRs (4)
- 2 genes of L chain on the variable region are randomly selected
- 3 genes of H chain on the variable region are randomly selected
- combination of unique Vl and VH, which rearrange independently of each other create a unique combination that
- joins with the constant region during recombination to make super random and diverse BCRs
describe the gene recombination of the L chain of the BCR variable region
there are many versions of V genes and J genes and once of each is randomly selected
describe the gene recombination of the H chain of the BCR variable region
there are many versions of V genes, D genes, and J genes and one of each is randomly selected
describe the gene recombination of the constant region of the light chain of BCRs
random selection of either lambda or kappa genes
when does gene conversion occur in BCRs
when there are limited V gene options
what are pseudogenes?
sequences of DNA that are upstream of the V gene that do not code for anything but can be used to generate diversity
describe the process of gene conversion, which is mostly just for V genes (4)
- uracil will randomly be inserted in V gene
- uracil is then removed bc it is RNA, leaving a gap in the DNA
- randomly selected short segments from pseudogenes will be inserted to fill the gap
- now are left with different DNA sequence to make a different V gene
what will TCRs only bind to?
antigen expressed on MHC
what do T helper cells recognize?
antigen expressed on MHC II
what do cytotoxic T cells recognize?
antigen expressed on MHC I
what are the 2 classes of TCR?
- alpha:beta (the majority)
2. gamma:delta
describe the structure of TCRs
- 2 polypeptide chains
2. each chain has 1 variable and 1 constant region
which region of a TCR recognizes antigen/MHC complexes?
the variable region
how is diversity of TCRs achieved?
through gene recombination
describe gene recombination in alpha:beta TCRs
- alpha chain: has a V, J, and C (Constant) gene; the random selection of 1 V and 1 J gene are combined with the one constant gene of the alpha chain for diversity
- beta chain: random selection of 1 V, 1 D, and 1 J gene are combined with one of 2 possible C genes
give one big exception/cool thing about generation of TCR diversity in the beta chain that leads to more diversity
D gene selection is optional and you can also select for more than one D gene, increasing the number of possibilities
where does junctional diversity occur?
where the different selected genes join
what are the 2 types of junctional diversity?
- base insertion
2. base deletion
describe base insertion of junctional diversity
random nucleotides inserted at V, D, and J junctions
how many nucleotides can randomly be added between V and D genes in base insertion?
up to 5
how many nucleotides can randomly be added between D and J genes in base insertion?
up to 4
describe base deletion of functional diversity
random nucleotides may be removed
where is MHC I found?
on all nucleated cells
what is MHC I recognized by?
cytotoxic T cells
where is MHC II found? (3)
- dendritic cells
- macrophages
- B cells
what is MHC II recognized by?
helper T cells
what does MHC I do?
presents antigen from intracellular/endogenous locations
what is presented on MHC if normal cellular processes are occurring? what is the result?
self-antigen is presented and there is no immune response
what is presented on MHC I if a cell is infected with a virus or something? what is the result?
non-self antigen is present and initiates an immune response
what does MHC II do?
presents antigen from exogenous locations
describe MHC II’s present of mostly non-self antigen
antigen is phagocytosed/endocytosed, processed, then presented on MHC II
