How the immune system recognises pathogens Flashcards
What is an epitope?
Another name for a determinant- the part of an antigen bound by an immune cell
Which part of the immune system recognises the most amount of antigens?
The adaptive immune system- recognise millions - Innate immune system only recognise a few
Describe the recognition of antigens by B and T cell receptors
B and T cells can recognise many different antigens but only a few of these cells can recognise each antigen. Once an antigen binds to one of the few B or T cells with the correct receptor, the cell will divide and produce daughter cells with the same receptor
What do B cells use to recognise antigens?
Immunoglobulins (antibodies).
Describe the determinants recognised B cell receptors?
Usually conformational- shapes formed by protein folding
What happens when a B cell receptor is activated?
- They differentiate into plasma cells
2. They secrete antibodies with specificity identical to the B cell receptor
Draw and label the structure of a typical antibody- Describe what each part does
Must have a variable regions where the antigen binds. Variable regions attached to the light chain
Must have a constant region- called heavy chains- controls what the antibody does
Light chain and heavy chain joined by a disulfide bonds
What is class switching?
When B cells are able to change the isotype of class of there antibody
Which class do B cell start with and what can it switch into?
B cells start with IgM- This can switch into IgG, IgA, or IgE
What happens to the specificity and function of an antibody when it switches?
Specificity stays constant
Biological effect and function may change
Which antibody class is made first in an immune response? Which can sometimes be made second?
IgM
Sometimes second- IgG
How is receptor diversity on B cells obtained?
Gene segments within heavy and light chain loci are mixed and matched
Name of gene segments which are mixed and matched to obtain B cell diversity. How many of each segment is there?
Variable region 40
Diversity region 25
Joining region 6
Describe the process of somatic DNA recombination
Region of germ line DNA is randomly spliced- D-J segments come together. Which segments come together is random
Another recombination event happens- region of DNA is spliced at random- V region joins D-J region
Transcription occures f the sequence, Messenger RNA is produced, Exons are removed from splicing, Translation occurs to produce heavy chain
What must happen to an antigen before a T cell receptor recognises it?
Must be presented by an antigen presenting cell using MHC- Histocompatibility complex
Draw and label the structure of a T cell receptor
has 2 chains, alpha and Beta
Held together by disulfide bonds
Have a cytoplasmic tail which penetrates the cytoplasm
Has 2 variable and 2 constant regions one on each chain.
Each variable and constant region has a carbohydrate molecule attached to it
When do T cells begin to express T cell receptors?
When they are still developing in the thymus
Describe the generation of diversity in T cell receptors
Conducted in germ line DNA for the alpha and beta loci on TCR
Recombination of VDJ segments in a random manner, with the addition of nucleotides to produce receptors
Which chromosome codes for the production alpha chain in T cells?
chr 14
Which chromosome codes for the production Beta chain in T cells?
Chr 7
What is the most potent antigen presenting cell?
Dendritic cells
What does MHC and HLA stand for?
MHC: major histocompatability complex
HLA (Man): human leukocyte antigens
Name the different types of MHC molecules, what do they present to
MHC class 1- CD8+ T cells MHC class2- CD4+ T cells
Where will you find MHC class 1 and MHC class 2 molecules?
Class 1- all cells
Class 2- antigen presenting cells only
