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Immunity, Infection and Haematology > Recognition of antigen by the adaptive immune system > Flashcards

Recognition of antigen by the adaptive immune system Flashcards

1
Q

What are the cells of the adaptive immune system?

A

B cells, T cells

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2
Q

What are antigens?

A

Molecules that induce an immune response through the activation of antigen specific lymphocytes

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3
Q

What are the three groups of molecules that work together to recognise antigen for the adaptive immune system?

A

MHC, B cell receptors, T cell receptors

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4
Q

What is combinatorial diversity?

A

Diversity achieved through a process of gene rearrangement of the different parts encoding the receptor

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5
Q

How do B cell receptors achieve further diversity and specificity for antigen?

A

Through a process of rapid mutation called hypermutation

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6
Q

What do T lymphocytes recognise?

A

Short peptide sequences from antigens, not whole pathogens

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7
Q

What does an APC have to do in order for a T lymphocyte to be able to recognise a pathogen?

A

Break down the pathogen and process into smaller peptides within the APC

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8
Q

How do T lymphocytes recognise peptides?

A

The peptides must be presented on the APC cell surface

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9
Q

How are peptides presented on the APC cell surface for recognition by T cells?

A

By a peptide-presenting molecule - Major histocompatibility complex (MHC)

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10
Q

What do B lymphocytes recognise?

A

whole antigen

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11
Q

How do B lymphocytes recognise antigen?

A

Through their B cell receptor which binds to cell surface molecules or patterns.

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12
Q

What is the difference between a B cell receptor and an antibody/immunoglobulin?

A

Antibodies/immunoglobulins are soluble antigen receptors secreted from terminally differentiated B cells (plasma cells)

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13
Q

What do B cells/antibodies do once they have bound to antigens?

A

Present to T cells

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14
Q

What does MHC class I recognise?

A

Peptides derived from endogenous proteins

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15
Q

What does MHC class II recognise?

A

Peptides processed from exogenous proteins

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16
Q

Where are MHC class I molecules found?

A

All nucleated cells, except neurones

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17
Q

What is a proteosome?

A

A large cytoplasmic complex involved in the breakdown of proteins

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18
Q

Where do the broken down peptides (antigens) go?

A

Through the endoplasmic reticulum to the surface and loaded into the peptide-binding groove of a MHC class I molecule

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19
Q

What type of cell recognises the MHC class I: peptide complex?

A

Cytotoxic T cells

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20
Q

What do cytotoxic T cells express that facilitate the interaction between the T cell and the MHC class I?

A

CD8 - a co-receptor for the T cell receptor (TCR)

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21
Q

What does the process of specific antigen recognition trigger the cytotoxic T cell to do?

A

Kill the virally infected cell by inducing apoptosis

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22
Q

What does the TAP protein do?

A

Controls the movement of these intracellular proteins into the endoplasmic reticulum

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23
Q

What two proteins assist the folding of MHC?

A

calnexin and calreticulin

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24
Q

Why are calnexin and calreticulin needed?

A

Because the protein is relatively unstable before it has bound peptide

25
Q

What retains a pool of MHC in the ER?

A

Protein Tapasin

26
Q

Why is there a need for a pool of MHC to be retained in the ER?

A

So that a rapid increase in surface peptide/MHC complexes can occur following peptide bonding

27
Q

Which cells express MHC class II on their surface?

A

Antigen presenting cells e.g. dendritic cells, monocytes/macrophages, B cells

28
Q

What is the peptide binding groove of the MHC class II complexed with, before it reaches the ER?

A

Invariant chain

29
Q

Where is the invariant chain degraded?

A

in the ER

30
Q

What does HLA-DM do?

A

Catalyse the insertion of the antigenic peptide or epitope into the peptide binding groove of an MHC class II molecule

31
Q

What does MHC class II interact with?

A

CD4 receptor on T cell

32
Q

What does the cytokine environment following interaction with CD4 cause the T cell to do?

A

Polarise to become either a memory cell or one of a number of effector cell phenotypes

33
Q

What are the commonest effector cell phenotypes for T cells?

A

Th1, Th2, Tregulatory and Th17 cells

34
Q

Where do B cells develop?

A

Firstly within the bone marrow and then secondly in secondary lymphoid organs when they encounter antigen

35
Q

What is a molecule of immunoglobulin composed of?

A

a pair of identical heavy chains and a pair of identical light chains

36
Q

What type of bond connects the pair of heavy chains?

A

Disulphide bond

37
Q

What type of bond connects each heavy chain to a light chain?

A

Disulphide bond

38
Q

What is the gross structure of IgG molecule?

A

three globular regions linked together by a flexible hinge region

39
Q

What enzyme digests the globular regions?

A

papain

40
Q

What do accessory/signalling molecules do?

A

Required to signal the inside of the cell when antigen is bound

41
Q

Why can’t surface Ig molecules signal the inside of the cell when antigen is bound?

A

The cytoplasmic tail is too short

42
Q

What is the best known accessory molecule often used in labs to identify B cells?

A

CD19

43
Q

How many hypervariable regions does each variable domain have?

A

3

44
Q

What forms the surface that binds to the antigen on an immunoglobulin molecule?

A

The hypervariable regions

45
Q

What are the two types of light chain?

A

Kappa or lamda

46
Q

What are the five types of heavy chain?

A

mu, gamma, delta, epsilon, alpha

47
Q

What do the constant domains determine?

A

the function of the antibody molecule

48
Q

What is a TCR compose of?

A

two non-identical Ig-domain polypeptide chains

49
Q

What are the two types of T cells distinguished by?

A

Expression of either alpha and beta TCR chains or gamma and delta chains

50
Q

What accessory signalling molecule is used by the TCR?

A

CD3 complex

51
Q

What is somatic recombination?

A

Mechanism by which the immune system can combat the diversity of pathogens

52
Q

What are the gene segments encoding for variable regions of the heavy and light chains of Ig and the alpha-beta or gamma-delta chains of the TCR?

A 
Variable domain gene (V)
Diversity gene (D)
Joining gene (J)
Constant domain genes (C)
53
Q

What enzymes are required for gene rearrangement?

A

RAG-1 and RAG-2

54
Q

What happens in the absence of RAG-1 and RAG-2?

A

Neither B nor T cells develop and infants suffer severe life threatening infections due to Severe Combined Immunodeficiency Disease

55
Q

What is the first step of gene rearrangement?

A

Combine the D and J segments of the heavy chain or TCRβ chain

56
Q

What is the second step of gene rearrangement?

A

Join the V segment to the DJ.

57
Q

What happens once the mRNA for the V and C segments have been synthesised?

A

They are spliced together and translated

58
Q

What is different about the gene rearrangement for the light chain and TCRα chain?

A

There are only V and J segments for the variable region

59
Q

How is additional diversity created in the light chain and TCRα chain?

A

By the addition of nucleotides at the junctional site by the enzyme terminal deoxynucleotidyl transferase (tdt)

Immunity, Infection and Haematology (6 decks)

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