How the immune system recognises pathogens Flashcards

1
Q

What is an epitope?

A

Another name for a determinant- the part of an antigen bound by an immune cell

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2
Q

Which part of the immune system recognises the most amount of antigens?

A

The adaptive immune system- recognise millions - Innate immune system only recognise a few

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3
Q

Describe the recognition of antigens by B and T cell receptors

A

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

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4
Q

What do B cells use to recognise antigens?

A

Immunoglobulins (antibodies).

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5
Q

Describe the determinants recognised B cell receptors?

A

Usually conformational- shapes formed by protein folding

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6
Q

What happens when a B cell receptor is activated?

A
  1. They differentiate into plasma cells

2. They secrete antibodies with specificity identical to the B cell receptor

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7
Q

Draw and label the structure of a typical antibody- Describe what each part does

A

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

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8
Q

What is class switching?

A

When B cells are able to change the isotype of class of there antibody

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9
Q

Which class do B cell start with and what can it switch into?

A

B cells start with IgM- This can switch into IgG, IgA, or IgE

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10
Q

What happens to the specificity and function of an antibody when it switches?

A

Specificity stays constant

Biological effect and function may change

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11
Q

Which antibody class is made first in an immune response? Which can sometimes be made second?

A

IgM

Sometimes second- IgG

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12
Q

How is receptor diversity on B cells obtained?

A

Gene segments within heavy and light chain loci are mixed and matched

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13
Q

Name of gene segments which are mixed and matched to obtain B cell diversity. How many of each segment is there?

A

Variable region 40
Diversity region 25
Joining region 6

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14
Q

Describe the process of somatic DNA recombination

A

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

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15
Q

What must happen to an antigen before a T cell receptor recognises it?

A

Must be presented by an antigen presenting cell using MHC- Histocompatibility complex

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16
Q

Draw and label the structure of a T cell receptor

A

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

17
Q

When do T cells begin to express T cell receptors?

A

When they are still developing in the thymus

18
Q

Describe the generation of diversity in T cell receptors

A

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

19
Q

Which chromosome codes for the production alpha chain in T cells?

A

chr 14

20
Q

Which chromosome codes for the production Beta chain in T cells?

A

Chr 7

21
Q

What is the most potent antigen presenting cell?

A

Dendritic cells

22
Q

What does MHC and HLA stand for?

A

MHC: major histocompatability complex

HLA (Man): human leukocyte antigens

23
Q

Name the different types of MHC molecules, what do they present to

A
MHC class 1- CD8+ T cells
MHC class2- CD4+ T cells
24
Q

Where will you find MHC class 1 and MHC class 2 molecules?

A

Class 1- all cells

Class 2- antigen presenting cells only

25
Q

What is the main structural difference between MHC class 1 and MHC class 2 molecules

A

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

26
Q

On which chromosome is the alpha and beta parts of MHC molecules located?

A

Chr 6

27
Q

Which type of peptides do MHC class 1 and class 2 molecules bind to?

A

Any that can fit into the structural groove- not a single peptide- collection of peptides

28
Q

What two things determine MHC binding?

A

Fit between amino acid side chains of the pathogenic peptide and pockets in the peptide binding groove of MHC molecules

29
Q

Two properties of MHC which ensure the maximum number of peptides can be presented to it

A
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
30
Q

What is Coeliac disease? What genetic/ Immunological quality do people with the disease have?

A
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
31
Q

Why do people with Coeliac disease have veyr specific MHC molecules? What are these molecules?

A

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

32
Q

Which part of gluten initiates an immune response in people with Coeliac disease

A

Gliadin peptide

33
Q

What is immunological tolerance?

A

When the immune system attempts to eliminate or control potentially self reactive cells

34
Q

Describe the process of central tolerance

A

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

35
Q

Describe the process of peripheral tolerance

A

When self reactive lymphocytes escape deletion during development but can be controlled (killed) in the periphery by regulatory T cells (Treg)

36
Q

Describe the functions of regulatory T cells (Treg)

A

It has immunosurppressive effects-

Eliminates self reactive lymphocytes in the periphery