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Immunology > Antigen processing/recognition by T lymphocytes > Flashcards

Antigen processing/recognition by T lymphocytes Flashcards

1
Q

B cells can bind to _____, while T cells need to be_____

A

Native antigens; introduced to antigens thru APCs

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2
Q

TCR antigen recognition

A

Only in the form of peptide bound to an MHC molecule on the surface of APC

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3
Q

Antigen processing

A

Pathogen-derived proteins must be degraded into peptides

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4
Q

Peptide:MHC complex

A

Displayed on APC surfaces, where they can be recognized by T cells

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5
Q

Antigen presentation

A

Binding of peptide:MHC complex and its expression on APC

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6
Q

2 classes of MHC

A

MHC molecules bind a variety of peptides in different intracellular compartments

  • CD8 binds alpha-3 domain of MHC class 1
  • CD4 binds the beta-2 domain of MHC class 2
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7
Q

TCR specifically binds ______

A

BOTH peptide and MHC molecules

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8
Q

Professional antigen-presenting cells

A
  • dendritic cells
  • macrphage
  • B cell
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9
Q

Dendritic cell

A
  • Cell type: viral
  • Location in lymph node: T cell area
  • Antigen uptake: macropinocytosis/phagocytosis (+++) universal antigen uptake
  • MHC expression: low on tissue DCs, high on lymphoid tissue DCs
  • Co stimulator delivery: constitutive, nonphagocytic lymphoid DCs (++++)
  • Antigen presented: peptides, viral, allergens
  • Location: ubiquitous
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10
Q

Macrophage

A
  • Cell type: bacterium
  • Location in lymph node: ??
  • Antigen uptake: phagocytosis (+++)
  • MHC expression: inducible by bacteria and cytokines (- to +++)
  • Co stimulator delivery: Inducible (- to +++)
  • Antigen presented: particulate antigens, intra/extracellular pathogens
  • Location: lymphoid tissue, connective tissue, body cavity
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11
Q

B cell

A
  • Cell type: microbial toxin
  • Location in lymph node: follicle
  • Antigen uptake: antigen-specific receptor (++++)
  • MHC expression: constitutive, increases on activation (+++ to ++++)
  • Co stimulator delivery: inducible (- to +++)
  • Antigen presented: soluble antigens, toxins, viruses
  • Location: lymphoid tissue, peripheral blood
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12
Q

What cell type is the best APC?

A

Dendritic cells

- are widely distributed in the body, can present any possible antigen derived peptide

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13
Q

What makes a cell “professional”?

A

Able to activate T cells

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14
Q

What is the difference between immature and mature cells?

A

Immature: uptake and process antigens (little MHC class 2)

Mature: present antigen (lots of MHC class 2)

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15
Q

How do DC mature?

A

DC take up bacterial antigens in the skin and then move to enter a draining lymphatic vessel –> DCs bearing antigen enter draining lymph node where they settle in the T cell areas
mature on taking antigen from infected sites to secondary lymphoid organs

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16
Q

Where is MHC located in immature T cells?

A

All MHC class 2 are inside, as MHC moves to the surface the cell matures

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17
Q

Classical model

A

Migration of immature DC from the periphery to the T cell areas of the lymph nodes only occurs in response to microbial stimulation
- pathogen induced migration

18
Q

Revised model

A

Steady state migration occurs constitutively in the apparent absence of microbial stimulation

  • mechanism by which DC can sample and engulf self proteins and food antigens to naive T cells to establish/maintain peripheral tolerance
  • pathogen induced migration
19
Q

Direct presentation

A

Peptides generated in cytosol are transported to ER, where they bind MHC class 1 molecules and presented to CD8+ T cells

20
Q

Direct presentation (CD4)

A

Peptides generated in acidified intracellular vesicles presented by MHC class 2 molecules to CD4+ T cells

21
Q

Cross presentation

A

Allows extracellular antigens to be processed and displayed within MHC class 1 molecules to CD8+ T cells (in addition to MHC class 2 and CD4+ T cells)

22
Q

Receptor mediated endocytosis of bacteria

A
  • MHC class 2

- CD4 T cell

23
Q

Marcopinocytosis of bacteria or viruses

A
  • MHC class 2

- CD4 T cell

24
Q

Viral infection

A
  • MHC class 1

- CD8 T cell

25
Q

Cross presentation of exogenous viral antigens

A
  • MHC class 1

- CD8 T cell

26
Q

Transfer of viral antigens from infected DC to resident DC

A
  • MHC class 1

- CD8 T cell

27
Q

Questions that only cross presentation can answer

A
  • How to CD8+ T cell responses are primed to infectious organisms that do not infect APCs?
  • How can DCs prime cytotoxic T cells against pathogens that are restricted to the endocytic pathway and never reach the cytosol?
  • Pathogen infected DCs are often functionally compromised, how can they present antigens efficiently?
28
Q

Autophagy

A

Presentation of cellular antigens by MHC class 2 molecules

29
Q

Exceptions to the rules of antigen presentation

A
  • cross presentation

- autophagy

30
Q

Why is yeast used in immunology research?

A

Can generate multiple clones quickly

31
Q

How does autophagy control innate and adaptive immunity?

A
  • direct pathogen elimination
  • regulation and effector function of PRRs
  • regulation of inflammasome activation and alarmin secretion
  • cytoplasmic Ag processing for MHC 2 presentation and T cell homeostasis
32
Q

Macroautophagy

A

immunological autophagy

33
Q

How are MHC 1 molecules expressed on APCs

A

+++ on T cells, B cells, macrophages, DC, and neutrophils

+ on thymic epithelium, liver hepatocytes, kidney epithelium, and brain

34
Q

How are MHC 2 molecules expressed on APCs

A

+++ on B cells and DC
+ on T cells
++ on macrophages

+++ on thymic epithelium

35
Q

Erythrocytes

A

Do not express either MHC 1 or 2

36
Q

Degenerate (promiscuous) binding specificity

A

MHC molecules have peptide binding sites that are capable of binding peptides of many different amino acid sequences
- MHC have germline configuration = less diversity, so they need to be promiscuous

37
Q

Peptide binding groove

A

Peptide binding site on the surface of the MHC molecule within which a single peptide is held tightly by non covalent bonds

38
Q

What do alpha/beta TCRs recognize?

A

Peptide presented at cell surfaces by MHC molecules

39
Q

Where do peptides bind to MHC class 1?

A

Endoplasmic reticulum

40
Q

Where are MHC class 2 peptides generated?

A

In acidified intracellular vesicles

41
Q

Cross presentation enables ____

A

Professional APCs to stimulate cytotoxic CD8 T cell responses against viruses that do not infect them directly

Immunology (28 decks)

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