Adaptive Immunity 3

Question 1

Why do T-cells need antigen presentation?

Answer 1

• Unlike B cells, T cells do not recognise native antigen!
• Antigen must be processed and presented to them before they can see antigen and then respond to that antigen in the appropriate way

Question 2

There are three main types of professional antigen-presenting cell: these are…

Answer 2

• Dendritic cells (DCs), which have the broadest range of antigen presentation, and are probably the most important APC. Activated DCs are especially potent TH cell activators because, as part of their composition, they express co-stimulatory molecules such as CD80 and CD86.
• Macrophages are very effective at engulfing pathogens and then processing them into immunogenic peptides
• B cells can internalize the antigen, which binds to its BCR and present it incorporated to MHC II molecule, but are inefficient APC for most other antigens

Question 3

… cells, which have the broadest range of antigen presentation, and are probably the most important APC. Activated … are especially potent TH cell activators because, as part of their composition, they express co-stimulatory molecules such as CD80 and CD86.

Answer 3

Dendritic cells (DCs), which have the broadest range of antigen presentation, and are probably the most important APC. Activated DCs are especially potent TH cell activators because, as part of their composition, they express co-stimulatory molecules such as CD80 and CD86.

Question 4

… are very effective at engulfing pathogens and then processing them into immunogenic peptides

Answer 4

Macrophages are very effective at engulfing pathogens and then processing them into immunogenic peptides

Question 5

B cells can internalize the antigen, which binds to its BCR and present it incorporated to … … molecule, but are inefficient APC for most other antigens

Answer 5

B cells can internalize the antigen, which binds to its BCR and present it incorporated to MHC II molecule, but are inefficient APC for most other antigens

Question 6

Activation of T cells

• … (APCs) determine which peptides will be presented on Class I and Class II … during initial activation
• T cells need to be able to distinguish between external antigens (taken up by APCs) and internal antigens (infected cell)

Answer 6

• Antigen presenting cells (APCs) determine which peptides will be presented on Class I and Class II MHC during initial activation
• T cells need to be able to distinguish between external antigens (taken up by APCs) and internal antigens (infected cell)

Question 7

Activation of T cells

• Antigen presenting cells (APCs) determine which peptides will be presented on Class I and Class II MHC during initial activation
• T cells need to be able to distinguish between external antigens (taken up by …) and internal antigens (… cell)

Answer 7

• Antigen presenting cells (APCs) determine which peptides will be presented on Class I and Class II MHC during initial activation
• T cells need to be able to distinguish between external antigens (taken up by APCs) and internal antigens (infected cell)

Question 8

What is Antigen Processing?

• Enzymatic process of degrading … through … which results in breaking down of proteins into … peptides
• Antigen processing requires … (…) and movement of endocytic vesicles

Answer 8

• Enzymatic process of degrading proteins through proteolysis which results in breaking down of proteins into antigenic peptides
• Antigen processing requires energy (ATP) and movement of endocytic vesicles

Question 9

What is Antigen Processing?

• Enzymatic process of degrading proteins through proteolysis which results in breaking down of proteins into antigenic …
• Antigen processing requires energy (ATP) and movement of endocytic …

Answer 9

• Enzymatic process of degrading proteins through proteolysis which results in breaking down of proteins into antigenic peptides
• Antigen processing requires energy (ATP) and movement of endocytic vesicles

Question 10

Cellular Compartments - Exogenous Antigens vs Endogenous Antigens

• Before antigen can be presented, it must be processed (protein into antigenic peptides)
• MHC Class I - … antigen (E…) - Peptides are made by proteases in proteosome - transported into endoplasmic reticulum to be further processed - Antigens presented in context of MHC Class I are recognised by … … T cells
• MHC Class II - … antigen (E…) - Endocytosis of antigen - once inside cell, encased within endosomes - become acidic and activate proteases to degrade the antigen - MHC Class II are then exported to endocytic vesicles where the bind peptide antigen and travel to cell surface - recognised by … cells

Answer 10

• Before antigen can be presented, it must be processed (protein into antigenic peptides)
• MHC Class I - Intracellular antigen (Endogenous) - Peptides are made by proteases in proteosome - transported into endoplasmic reticulum to be further processed - Antigens presented in context of MHC Class I are recognised by CD8 cytotoxic T cells
• MHC Class II - Extracellular antigen (Exogenous) - Endocytosis of antigen - once inside cell, encased within endosomes - become acidic and activate proteases to degrade the antigen - MHC Class II are then exported to endocytic vesicles where the bind peptide antigen and travel to cell surface - recognised by CD4 T helper cells

Question 11

Cellular Compartments - Exogenous Antigens vs Endogenous Antigens

• Before antigen can be presented, it must be processed (protein into antigenic …)
• MHC Class I - Intracellular antigen (Endogenous) - Peptides are made by … in proteosome - transported into endoplasmic reticulum to be further processed - Antigens presented in context of MHC Class I are recognised by CD8 cytotoxic T cells
• MHC Class II - Extracellular antigen (Exogenous) - Endocytosis of antigen - once inside cell, encased within endosomes - become acidic and activate … to degrade the antigen - MHC Class II are then exported to … vesicles where the bind peptide antigen and travel to cell surface - recognised by CD4 T helper cells

Answer 11

• Before antigen can be presented, it must be processed (protein into antigenic peptides)
• MHC Class I - Intracellular antigen (Endogenous) - Peptides are made by proteases in proteosome - transported into endoplasmic reticulum to be further processed - Antigens presented in context of MHC Class I are recognised by CD8 cytotoxic T cells
• MHC Class II - Extracellular antigen (Exogenous) - Endocytosis of antigen - once inside cell, encased within endosomes - become acidic and activate proteases to degrade the antigen - MHC Class II are then exported to endocytic vesicles where the bind peptide antigen and travel to cell surface - recognised by CD4 T helper cells

Question 12

There are two alternative pathways for antigen processing; the … pathway and … pathway

Answer 12

There are two alternative pathways for antigen processing; the exogenous pathway and endogenous pathway

Question 13

Exogenous antigens - pathogens that are processed via the exogenous antigen presentation pathway.

• This pathway involves the … of the pathogen and the subsequent breakdown of its proteins into peptides in a phagolysosome. These peptides are complexed with MHC … molecules and shuttled to the cell surface where they are presented to …+ T cells

Answer 13

• This pathway involves the endocytosis of the pathogen and the subsequent breakdown of its proteins into peptides in a phagolysosome. These peptides are complexed with MHC II molecules and shuttled to the cell surface where they are presented to CD4+ T cells

Question 14

Endogenous antigens

• Broken down in the … before being transported via the TAP proteins to the endoplasmic reticulum. They are complexed with MHC … … molecules in the golgi prior to presentation on the cell surface to …+ T cells

Answer 14

• Broken down in the proteasome before being transported via the TAP proteins to the endoplasmic reticulum. They are complexed with MHC class I molecules in the golgi prior to presentation on the cell surface to CD8+ T cells

Question 15

MHC class … complexed peptides are recognised by CD4+ T cells and MHC class … complexed peptides are recognised by CD8+ T cells

Answer 15

MHC class II complexed peptides are recognised by CD4+ T cells and MHC class I complexed peptides are recognised by CD8+ T cells

Question 16

Antigens require … before they can be “seen” by T cells

Answer 16

Antigens require processing before they can be “seen” by T cells

Question 17

The professional antigen presenting cells include … cells, … and … cells

Answer 17

The professional antigen presenting cells include dendritic cells, macrophage and B cells

Question 18

• There are two alternative pathways for antigen processing; the exogenous pathway and endogenous pathway:
  
  • Endogenous antigens inside the cell are presented on Class … MHC molecules to CD…+ T cells
  • Exogenous antigens in endosomes presented on Class … MHC molecules to CD…+ T cells

Answer 18

• There are two alternative pathways for antigen processing; the exogenous pathway and endogenous pathway:
  
  • Endogenous antigens inside the cell are presented on Class I MHC molecules to CD8+ T cells
  • Exogenous antigens in endosomes presented on Class II MHC molecules to CD4+ T cells

Question 19

• There are two alternative pathways for antigen processing; the exogenous pathway and endogenous pathway:
  
  • … antigens inside the cell are presented on Class I MHC molecules to CD8+ T cells
  • … antigens in endosomes presented on Class II MHC molecules to CD4+ T cells

Answer 19

• There are two alternative pathways for antigen processing; the exogenous pathway and endogenous pathway:
  
  • Endogenous antigens inside the cell are presented on Class I MHC molecules to CD8+ T cells
  • Exogenous antigens in endosomes presented on Class II MHC molecules to CD4+ T cells

Question 20

Endogenous Antigens - Generation of Class I MHC Peptides

• Endogenous antigens are from proteins produced … the cell
• These includes … protein antigens and … protein antigens
• Class I MHC antigens activate cytotoxic … T-cells for killing infected cells and tumour cells

Answer 20

• Endogenous antigens are from proteins produced inside the cell
• These includes self protein antigens and foreign protein antigens
• Class I MHC antigens activate cytotoxic CD8 T-cells for killing infected cells and tumour cells

Question 21

Endogenous Antigens Proteasome

• There are different proteasomes that generate peptides for MHC class-I presentation: …S proteasome (or standard proteasome), which is expressed by most cells; the … proteasome, which is expressed by many immune cells; and the …-specific proteasome expressed by … epithelial cells.

Answer 21

• There are different proteasomes that generate peptides for MHC class-I presentation: 26S proteasome (or standard proteasome), which is expressed by most cells; the immunoproteasome, which is expressed by many immune cells; and the thymic-specific proteasome expressed by thymic epithelial cells.

Question 22

Endogenous Antigens - transported by TAP proteins

• TAP proteins (… associated with … …)
• TAP 1 and TAP 2 form … in membrane of ER to facilitate selective transport of peptides from cytoplasm into lumen of ER
• TAP pump preferentially transport peptides with a length of 8–16 amino acids

Answer 22

• TAP proteins (Transporters associated with Antigen Processing)
• TAP 1 and TAP 2 form heterodimer in membrane of ER to facilitate selective transport of peptides from cytoplasm into lumen of ER
• TAP pump preferentially transport peptides with a length of 8–16 amino acids

Question 23

Endogenous Antigens - transported by TAP proteins

• TAP proteins (Transporters associated with Antigen Processing)
• TAP 1 and TAP 2 form heterodimer in membrane of … to facilitate selective transport of peptides from cytoplasm into lumen of …
• TAP pump preferentially transport peptides with a length of …-… amino acids

Answer 23

• TAP proteins (Transporters associated with Antigen Processing)
• TAP 1 and TAP 2 form heterodimer in membrane of ER to facilitate selective transport of peptides from cytoplasm into lumen of ER
• TAP pump preferentially transport peptides with a length of 8–16 amino acids

Question 24

MHC class I molecules are expressed on the cell surface of all … cells and present peptide fragments derived from intracellular proteins

Answer 24

MHC class I molecules are expressed on the cell surface of all nucleated cells and present peptide fragments derived from intracellular proteins

Question 25

MHC class … molecules are expressed on the cell surface of all nucleated cells and present peptide fragments derived from intracellular proteins

Answer 25

MHC class I molecules are expressed on the cell surface of all nucleated cells and present peptide fragments derived from intracellular proteins

Question 26

MHC class … molecules are selectively expressed on antigen-presenting cells (APC) including dendritic cells (DC), macrophages, and B cells.

Answer 26

MHC class II molecules are selectively expressed on antigen-presenting cells (APC) including dendritic cells (DC), macrophages, and B cells.

Question 27

MHC class II molecules are selectively expressed on …-… … (…) including dendritic cells (DC), macrophages, and B cells.

Answer 27

MHC class II molecules are selectively expressed on antigen-presenting cells (APC) including dendritic cells (DC), macrophages, and B cells.

Question 28

The peptide-loading complex

• MHC Class I molecules are assembled in the ER and consist of two types of chain - polymorphic heavy chain and beta 2 microglobulin
• The heavy chain is stabilized by calnexin until beta 2 binds. Without peptides - further stabilized by … proteins.
• A Protein Loading Complex assembly consists of seven subunits, including the transporters associated with antigen processing (TAP1 and TAP2 – jointly referred to as TAP), the oxidoreductase ERp57, the MHC-I heterodimer, and the chaperones tapasin and calreticulin.
• Tapasin interacats with TAP - translocates peptides from cytoplasm to ER - prior to entering peptides are derived from degradation of proteins which can be viral or self originating

Answer 28

• MHC Class I molecules are assembled in the ER and consist of two types of chain - polymorphic heavy chain and beta 2 microglobulin
• The heavy chain is stabilized by calnexin until beta 2 binds. Without peptides - further stabilized by chaperone proteins.
• A Protein Loading Complex assembly consists of seven subunits, including the transporters associated with antigen processing (TAP1 and TAP2 – jointly referred to as TAP), the oxidoreductase ERp57, the MHC-I heterodimer, and the chaperones tapasin and calreticulin.
• Tapasin interacats with TAP - translocates peptides from cytoplasm to ER - prior to entering peptides are derived from degradation of proteins which can be viral or self originating

Question 29

CD8+ Tc Activated by Endogenous or Intracellular Antigens

• Effector CD8+ Tc (CTLs) are primarily needed for the eradication of … cells
• CTLs can also be activated against … cells (…) targets “neo antigens”

Answer 29

• Effector CD8+ Tc (CTLs) are primarily needed for the eradication of infected cells
• CTLs can also be activated against cancer cells (tumour) targets “neo antigens”

Question 30

CD8+ Tc Activated by Endogenous or Intracellular Antigens

• Effector CD8+ Tc (CTLs) are primarily needed for the eradication of infected cells
• CTLs can also be activated against cancer cells (tumour) targets “… antigens”

Answer 30

• Effector CD8+ Tc (CTLs) are primarily needed for the eradication of infected cells
• CTLs can also be activated against cancer cells (tumour) targets “neo antigens”

Question 31

CTL (Effector CD8+ Tc) Killing of Infected Target Cells

• Viruses must replicate … cells and many bacteria and parasites live … host cells
• Therefore antigens for stimulating CTLs come from … the cell because they signal an intracellular infection

Answer 31

• Viruses must replicate inside cells and many bacteria and parasites live inside host cells
• Therefore antigens for stimulating CTLs come from inside the cell because they signal an intracellular infection

Question 32

Immune Evasion

• Viruses can interfere with Class … MHC expression to escape killing by CTLs
• Herpes Simplex Virus (HSV) protein ICP47 can selectively bind to … and inhibit the transfer of peptides into ER
• Some parasites invade de-nucleated red blood cells, which do not express MHC …

Answer 32

• Viruses can interfere with Class I MHC expression to escape killing by CTLs
• Herpes Simplex Virus (HSV) protein ICP47 can selectively bind to TAP and inhibit the transfer of peptides into ER
• Some parasites invade de-nucleated red blood cells, which do not express MHC I

Question 33

How are peptides generated? - Exogenous Antigen Pathway

• Antigen is taken up into intracellular vesicles via endocytosis or phagocytosis - endosome has … pH - … when endosome fuses with … - activates proteases - digested into peptides in the phagolysosome - Vesicles containing peptide fuse with vesicles containing MHC Class … molecules - allows peptides to be loaded onto MHC Class …

Answer 33

• Antigen is taken up into intracellular vesicles via endocytosis or phagocytosis - endosome has neutral pH - acidification when endosome fuses with lysosome - activates proteases - digested into peptides in the phagolysosome - Vesicles containing peptide fuse with vesicles containing MHC Class II molecules - allows peptides to be loaded onto MHC Class II

Question 34

How are peptides generated? - Exogenous Antigen Pathway

• Antigen is taken up into intracellular vesicles via endocytosis or phagocytosis - … has neutral pH - acidification when endosome fuses with lysosome - activates proteases - digested into peptides in the … - Vesicles containing peptide fuse with vesicles containing MHC Class II molecules - allows peptides to be loaded onto MHC Class II

Answer 34

• Antigen is taken up into intracellular vesicles via endocytosis or phagocytosis - endosome has neutral pH - acidification when endosome fuses with lysosome - activates proteases - digested into peptides in the phagolysosome - Vesicles containing peptide fuse with vesicles containing MHC Class II molecules - allows peptides to be loaded onto MHC Class II

Question 35

How are peptides generated? - Exogenous Antigen Pathway

• Peptides bound to MHC Class … molecules are derived from … pathogens (and internalised TM proteins)
• … of endocytic vesicles activates proteases that degrade proteins into fragments
• These peptide fragments are loaded onto MHC class … molecules

Answer 35

• Peptides bound to MHC Class II molecules are derived from engulfed pathogens (and internalised TM proteins)
• Acidification of endocytic vesicles activates proteases that degrade proteins into fragments
• These peptide fragments are loaded onto MHC class II molecules

Question 36

Trafficking of MHC class II molecules

• MHC class II … and … chains associate in the ER
• In the trans golgi network, MHC class II is sorted into …
• These … deliver MHC class II to specialised compartments where peptide loading occurs

Answer 36

• MHC class II alpha and beta chains associate in the ER
• In the trans golgi network, MHC class II is sorted into vesicles
• These vesicles deliver MHC class II to specialised compartments where peptide loading occurs

Question 37

What prevents MHC Class II from binding “self” peptides in the ER?

Answer 37

• Invariant chain blocks binding of peptides to MHC Class II molecules in the ER
• Complex of MHC Class II and Invariant chain is transported through the golgi into a compartment terms MHC Class II compartment - Invariant chain is digested, leaving CLIP - Class II associated Invariant chain polypeptide
• CLIP blocks binding of peptides to MHC Class II in vesicles
• Exchanged for an antigen peptide derived from a protein degraded in endosomal pathway - requries chaperone HLA-DM or HLA-DO (B cells) - MHC Class II molecules loaded with foreign peptide are transported to cell membrane to present to CD4 T cells

Question 38

Exogenous Pathway - Class II MHC Peptide Loading

• Class II MHC loading takes place in endosomes where acidic pH is required for protein degradation into peptides
• … Chain is degraded and CLIP is exchanged with … peptide

Answer 38

• Class II MHC loading takes place in endosomes where acidic pH is required for protein degradation into peptides
• Invariant Chain is degraded and CLIP is exchanged with foreign peptide

Question 39

Exogenous Pathway - Class II MHC Peptide Loading

• Class II MHC loading takes place in endosomes where acidic pH is required for protein degradation into peptides
• Invariant Chain is degraded and … is exchanged with foreign peptide

Answer 39

• Class II MHC loading takes place in endosomes where acidic pH is required for protein degradation into peptides
• Invariant Chain is degraded and CLIP is exchanged with foreign peptide

Question 40

CD4+ Th Activated by Exogenous Antigens

• Foreign antigens/extracellular pathogens need to be taken up by … to get noticed by … cells of the immune system
• This leads to activation of macrophage and the production of secreted antibody by plasma cells

Answer 40

• Foreign antigens/extracellular pathogens need to be taken up by APCs to get noticed by Th cells of the immune system
• This leads to activation of macrophage and the production of secreted antibody by plasma cells

Question 41

CD4+ Th Activated by Exogenous Antigens

• Foreign antigens/extracellular pathogens need to be taken up by APCs to get noticed by Th cells of the immune system
• This leads to activation of … and the production of secreted … by plasma cells

Answer 41

• Foreign antigens/extracellular pathogens need to be taken up by APCs to get noticed by Th cells of the immune system
• This leads to activation of macrophage and the production of secreted antibody by plasma cells

Question 42

Immune Evasion Class II MHC

• Viral Inhibition of Class II MHC
  
  • … interferes with Class II upregulation in APCs
  • The … viral envelope protein, glycoprotein B, reduces MHC Class II processing and inhibits the production of invariant chain peptide
  • … interferes with Class II processing
• Pathogens that evade lysosomes
  
  • Leishmania & mycobacteria (tuberculosis) prevent phagosome-lysosome fusion

Answer 42

• Viral Inhibition of Class II MHC
  
  • Adenovirus interferes with Class II upregulation in APCs
  • The HSV viral envelope protein, glycoprotein B, reduces MHC Class II processing and inhibits the production of invariant chain peptide
  • HIV interferes with Class II processing
• Pathogens that evade lysosomes
  
  • Leishmania & mycobacteria (tuberculosis) prevent phagosome-lysosome fusion

Question 43

Immune Evasion Class II MHC

• Viral Inhibition of Class II MHC
  
  • Adenovirus interferes with Class II upregulation in APCs
  • The HSV viral envelope protein, glycoprotein B, reduces MHC Class II processing and inhibits the production of … chain peptide
  • HIV interferes with Class II processing
• Pathogens that evade lysosomes
  
  • Leishmania & mycobacteria (…) prevent phagosome-lysosome fusion

Answer 43

• Viral Inhibition of Class II MHC
  
  • Adenovirus interferes with Class II upregulation in APCs
  • The HSV viral envelope protein, glycoprotein B, reduces MHC Class II processing and inhibits the production of invariant chain peptide
  • HIV interferes with Class II processing
• Pathogens that evade lysosomes
  
  • Leishmania & mycobacteria (tuberculosis) prevent phagosome-lysosome fusion

Question 44

How are T-cell antigens kept apart?

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through … to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires …, Tapasin, etc control
  • Class II requires low pH for removal

Answer 44

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, Tapasin, etc control
  • Class II requires low pH for removal

Question 45

How are T-cell antigens kept apart?

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, Tapasin, etc control
  • Class II requires low pH for removal

Answer 45

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, Tapasin, etc control
  • Class II requires low pH for removal

Question 46

How are T-cell antigens kept apart?

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, Tapasin, etc control
  • Class II requires low pH for removal

Answer 46

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, Tapasin, etc control
  • Class II requires low pH for removal

Question 47

How are T-cell antigens kept apart?

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, …, etc control
  • Class II requires low … for removal

Answer 47

• Location, Location, Accessory Proteins
• Class I and Class II MHC molecules both traverse through ER to cell surface but load peptides in different cell compartments
• Control is through accessory proteins
  
  • Class I requires TAP, Tapasin, etc control
  • Class II requires low pH for removal

Question 48

Recap: T-cell dependent B-cell response

• Sequence of events:
  
  • Antigen binding to BCR provides “Signal 1” to B cell.
  • Antigen is internalised, processed and antigenic peptides are displayed on MHC for T cell recognition.
  • TH (helper T cell) recognises antigen-MHC complex via the T cell antigen receptor (TCR): provides “Signal 1” to T-cell.
  • CD80 on B-cell binding to CD… on T-cell provides “Signal 2” to T cell.
  • T-cell activation leads to up-regulation of CD40L which bind to CD40 providing “Signal 2” to B-cell.
  • Cytokine production by activated T cell also help to activate B-cell.
  • B-cell proliferates and differentiates into antibody secreting B-cell (plasma cell).

Answer 48

• Sequence of events:
  
  • Antigen binding to BCR provides “Signal 1” to B cell.
  • Antigen is internalised, processed and antigenic peptides are displayed on MHC for T cell recognition.
  • TH (helper T cell) recognises antigen-MHC complex via the T cell antigen receptor (TCR): provides “Signal 1” to T-cell.
  • CD80 on B-cell binding to CD28 on T-cell provides “Signal 2” to T cell.
  • T-cell activation leads to up-regulation of CD40L which bind to CD40 providing “Signal 2” to B-cell.
  • Cytokine production by activated T cell also help to activate B-cell.
  • B-cell proliferates and differentiates into antibody secreting B-cell (plasma cell).

Question 49

Recap: T-cell dependent B-cell response

• Sequence of events:
  
  • Antigen binding to BCR provides “Signal 1” to B cell.
  • Antigen is internalised, processed and antigenic peptides are displayed on MHC for T cell recognition.
  • TH (helper T cell) recognises antigen-MHC complex via the T cell antigen receptor (TCR): provides “Signal 1” to T-cell.
  • CD80 on B-cell binding to CD28 on T-cell provides “Signal 2” to T cell.
  • T-cell activation leads to up-regulation of CD…L which bind to CD… providing “Signal 2” to B-cell.
  • … production by activated T cell also help to activate B-cell.
  • B-cell proliferates and differentiates into antibody secreting B-cell (plasma cell).

Answer 49

• Sequence of events:
  
  • Antigen binding to BCR provides “Signal 1” to B cell.
  • Antigen is internalised, processed and antigenic peptides are displayed on MHC for T cell recognition.
  • TH (helper T cell) recognises antigen-MHC complex via the T cell antigen receptor (TCR): provides “Signal 1” to T-cell.
  • CD80 on B-cell binding to CD28 on T-cell provides “Signal 2” to T cell.
  • T-cell activation leads to up-regulation of CD40L which bind to CD40 providing “Signal 2” to B-cell.
  • Cytokine production by activated T cell also help to activate B-cell.
  • B-cell proliferates and differentiates into antibody secreting B-cell (plasma cell).