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WEEK 10 SEM 4 > Antigen recognition by T cells > Flashcards

Antigen recognition by T cells Flashcards

1
Q

What is the difference between where B and T cells work?

A

Bcells- remove pathogens outside body cells

T cells- remove pathogens inside body cells

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2
Q

What things do T cells remove?

A

intracellular
virus
bacteria
malignant cells

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3
Q

How do B cells recognise antigens?

A

directly through their surface immunoglobin receptors

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4
Q

What happens when a B cell gets activated?

A

Proliferation- make lots of identical B cells that can recognise the antigen
differentiate to plasma cells or memory cells

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5
Q

How do the antibodies work to get rid of the microbes?

A

neutralization- prevents binding antogen to receptor
opsonization- more likely phagocytosis
complement activation- lysis of microbes

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6
Q

What are the types of T cells?

A

alpha beta T cell receptor T cells

gamma-delta T cell receptor T cell

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7
Q

What kind of antigens do alpha beta T cell receptor T cells recognise?

A

peptide antigens -they need to be cell bound and bound to the major histocompatibility complex of antigen presenting cells (ie the peptides cannot be soluble)

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8
Q

What kind of antigens do gamma-delta T cell receptor T cells recognise?

A

non-peptide antigens

recognize mostly lipid antigens that are bound to different types of MHC molecules

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9
Q

What do antigen presenting cells do?

A

process antigens into peptides (onlny alpha beta T cell receptor T cells)

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10
Q

What do the peptides do?

A
  1. bind to MHC molecules of the antigen presenting cells
  2. peptide-MHC complex is presented on the surface of the antigen presenting cell
  3. t lymphocytes scan it with their receptors
  4. if they recognize the peptide MHC-complex, they get activated and proliferate
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11
Q

What do CD4+ T helper cells recognise?

A

CD4+ T helper cells recognize peptides displayed by MHC II molecules

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12
Q

What do CD8+ T helper cells recognise?

A

and CD8+ cytotoxic T cells recognize peptides displayed by MHC I molecules (peptides combined with MHC I)

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13
Q

What is MHC restriction of antigen recognition by T cells?

A

T cells can only see antigens only when combined with MHC

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14
Q

What are antigen presenting cells?

A

dendritic cell
macrophage
b cell

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15
Q

How do CD8+ T lymphocytes work?

A

need to be activated
when activated, they can recognise antigens on ALL nucleated cells
fight viruses e.g. hepatitis

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16
Q

What does naive mean?

A

havent been activated

are still in the secondary lymphoid organs

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17
Q

How are dendritic cells antigen presenting cells?

A

these are the only cells that can activate naïve T cells (CD4+ or CD8+)

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18
Q

How are macrophages APCs?

A

present antigens to previously activated naive T cells and activate them (activate effector T cells)

usually these are Th1 cells

this also leads to co activation of macrophages which allows them to kill the antigen

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19
Q

How are B cells APCs?

A

present antigens to previously activated naïve T cells and activate them (activate effector Tcells)

occurs in germinal centres in the lymph nodes and spleen
leads to co activation of B cells, and leads to production of antibodies

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20
Q

What is a germinal centre?

A

areas of B cell proliferation

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21
Q

Where are dendritic cells present?

A

skin, mucosa, airways, gut

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22
Q

What do dendritic cells detect?

A

microbes present in tissue and capture them

23
Q

Where are naive T cells?

A

in spleen and lymph nodes

24
Q

What does a dendritic cell do?

A
  1. detect pathogen
  2. take up by phagocytosis
  3. transport microbe from tissue to lymph node or spleen (where naive T cells are- antigens need to be presented here)
    once pathogens are detected, they are taken up by phagocytosis
  4. whilst transporting- they process microbes into peptides and present antigens to naive T cells
25
Q

Why do dendritic cells transport microbes to lymph nodes/spleen?

A

this is where naive T cells are

antigens need to be presented here

26
Q

What is the priming of the adaptive T cell mediated immune response?

A

is the link between the innate and adaptive immune system

27
Q

What are the 2 signals needed to activate the T cell?

A

Signal 1= not enough to activate T cell
Signal 2= stong costimulatory signal by B7 family, CD80 and CD86 ACTING on CD28 receptors on T cells

THEN T cell activated and proliferates

28
Q

What is the third signal needed to help T cells differentiate after being activated?

A

cytokine release=
Th1= bacterial infection (IL12)
Th2= parasitic infection (IL4)
CD8+ cytotoxic lymphocytes= viral infection

29
Q

What does Th1 cooperate with?

A

macrophages- to eliminate bacteria

30
Q

What does Th2 cooperate with?

A

B cells and mast cells- to eliminate parasites and allergies

31
Q

What do macrophages do?

A

Macrophages phagocytose microbes and present antigens to effector CD4+ T cells in particular Th1 cells

32
Q

What does IFN-gamma leads to a switch to?

A

IgG

33
Q

What does IL4 lead to a switch to?

A

IgE

34
Q

What are cytotoxic CD8+ T cells specialised to do?

A

-recognize viral antigens and mutated proteins (from cancerous cells) presented in combination with MHC I – eliminate these cells that are infected with a virus or are malignant

35
Q

How does a T cell recognise antigen?

A

T cell receptor recognises a complex (MHC MOLECULE PLUS PEPTIDE FROM PATHOGEN)
Tcell has groves that allows it to interact with the amino acid residues

36
Q

What is the structure of the T cell receptor?

A

2 chains
most common T CEL= alpha and beta
Less common T cell= gamma and delta

each chain has constant and variable domain

3 hypervariable domains (contact with antigen peptides)

37
Q

How are different T cell receptors generated?

A

rearrangement of gene segments - cutting light and heavy chain genes by RAG (in immunoglobins)

38
Q

What is MHC 1?

A
  • these bind and present peptides to CD8+ T cells
  • composed of an alpha chain and a short beta 2 macroglobulin chain
  • present in all nucleated cells
39
Q

What is MHC II?

A
  • bind and present peptides to CD4+ T cells
  • they are composed of an alpha chain and a beta chain
  • present on only the professional antigen presenting cells like dendritic cells and macrophages
40
Q

MHC present antigens to what?

A

alpha beta T cells

not gamma delta

41
Q

What are human MHC molecules also called?

A

HLA

42
Q

What is the function of CD4 and CD8 receptors?

A

make sure that MHC I binds to cytotoxic cells, and MHC II binds to helper cells

43
Q

What are CD4 and CD8 receptors coupled to?

A

tyrosine kinase receptors

they decrease the threshold for T cell activation as they are coupled to tyrosine kinases−and thus the T cells need to make contact with fewer peptide-MHC complexes

44
Q

How do you eliminate exogenous bacteria?

A
  1. phagocytes and eliminate

2. antibodies eliminate (neutralisation, opsonisation, and complement activation)

45
Q

How is an antigen presented to CD4+ T cells?

A
  1. bacteria taken in phagosome
  2. fuse with lysosome- break down bacteria
  3. put peptides from bacteria with MHC II (so CD4+ can recognise)- MHC II (protein exported fromgolgi fuses with the phagolysosome)
  4. Low pH in phagolysosome so invariant chain breaks down but CLIP remains (fragment on chain) in groove
  5. another MHCII molecule (HLA- DM) has high CLIP affinity and takes it
  6. now groove is free peptide from bacteria can bind
  7. when peptide fits, MHCII is stabilised
  8. travels to plasma membrane
  9. CD4 recognises it
46
Q

How are viruses taken up?

A

Proteins derived from virus are tagged with ubiquitin so that they can be recognized by lytic complexes called proteasome

47
Q

What doe proteasomes do?

A

proteasomes take up ubiquitinated proteins and breaks them down into peptides

there will be peptides from these viral proteins present in the cytosol•these peptides need to get into the endoplasmic reticulum where the MHC I is synthesized

48
Q

What is TAP?

A

transporter in the membrane of the endoplasmic reticulum

which takes up these viral peptides from the cytosol and transports them into the lumen of the endoplasmic reticulum

49
Q

Why cant viral proteins bind to MHC II?

A

the invariant chain blocks the groove for MHC II, and thus viral proteins in the ER cannot bind to MHC II

MHCI doesnt leave ER until binds to viral protein

50
Q

What can mycobacterium tuberculosis do?

A

block expression of MHC II

51
Q

What does Neisseria meningitidis do?

A

lowers expression of MHCI and MHCII

52
Q

What does herpes simplex virus do?

A

produces proteins which bind to and inhibits TAP transporters which transport viral peptides into the ER to bind to MHC I

53
Q

What does adenovirus do?

A

produce proteins which binds to MHC I molecules and prevent it from leaving the ER to the plasma membrane

WEEK 10 SEM 4 (8 decks)

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