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
What is the main structural difference between MHC class 1 and MHC class 2 molecules
MHC class 1- 3 alpha units (1,2,3) nd 1 beta subunit (Beta 2) which is a microglobulin
MHC class2- 2 ebta and 2 alpha subunits
On which chromosome is the alpha and beta parts of MHC molecules located?
Chr 6
Which type of peptides do MHC class 1 and class 2 molecules bind to?
Any that can fit into the structural groove- not a single peptide- collection of peptides
What two things determine MHC binding?
Fit between amino acid side chains of the pathogenic peptide and pockets in the peptide binding groove of MHC molecules
Two properties of MHC which ensure the maximum number of peptides can be presented to it
It is polygenic- more than one type of MHC class 1 and 2 molecules- each can bind a different range of pepetides It is polymorphic- Multiple alleles for each MHC gene type- most likely heterozygous. Inherit different MHC alleles within the population
What is Coeliac disease? What genetic/ Immunological quality do people with the disease have?
Chronic inflammation of the small intestines Inappropriate immune response to gluten. Only occurs in people with the MHC class 2 molecules HLA- DQ2 and HLA-DQ8
Why do people with Coeliac disease have veyr specific MHC molecules? What are these molecules?
MHC class 2 molecules HLA- DQ2 and HLA-DQ8
Only these MHC molecules can present gliadin peptides (found in gluten) to T cells- causing the disease
Which part of gluten initiates an immune response in people with Coeliac disease
Gliadin peptide
What is immunological tolerance?
When the immune system attempts to eliminate or control potentially self reactive cells
Describe the process of central tolerance
As T cells develop in the thymus, and B cells in the bone marrow, their receptors are tested for reactivity to self antigens. If self reactivity is too strong the lymphocytes are killed
Describe the process of peripheral tolerance
When self reactive lymphocytes escape deletion during development but can be controlled (killed) in the periphery by regulatory T cells (Treg)
Describe the functions of regulatory T cells (Treg)
It has immunosurppressive effects-
Eliminates self reactive lymphocytes in the periphery
