Chapter 8: T Cell-Mediated Immunity

Question 1

Two Stages of T Cell Mediated Immunity

Answer 1

• T-cell priming

- Effector function

Question 2

Who activates cells

Answer 2

• immature dendritic cells (Langerhans cells) take up antigen and migrate to a lymph node
• in lymph node they settle in the T cell areas and differentiate into mature dendritic cells with long fingers (dendrites)

Question 3

Dendritic cells change their function during their journey to the lymph node. T or F

Answer 3

• T
• immature dendritic cells are good at antigen up-take at the site of infection and mature dendritic cells are good at presenting to T cells in the lymph node

Question 4

Dendritic cells are adept and versatile at processing antigen from pathogens. Use several pathways to process and present antigens.

Answer 4

• uptake of antigens by phagocytosis which delivers antigen to endocytic vesciles for presentation by MHC class 2 molecules to CD4 T cells
• Viral infection of the dendritic cell delivers peptides processed in the cytosol to the ER for presentation by MHC class 1 molecules to CD8 T cells
• cross presentation of antigen between MHC 1 and 2 (poorly understood)
• antigens tale up on by one dendritic cell can be delivered to a second dendritic cell for presentation by MHC class 1 molecules to CD8 T cells

Question 5

Naive T cells first encounter antigen presented by ___________ cells in ______________ lymphoid tissues.

Answer 5

• dendritic
• secondary
• naive T cells encounter antigen during their recirculation through secondary lymphoid organs
• they leave the blood at high endothelial venules and enter the lymph-nod cortex, where they mingle with professional APC

Question 6

Who are the professional APC?

Answer 6

• dendritic cells, macrophages, and B-cells in that order

Question 7

T cells that do not encounter their specific antigen….

Answer 7

• leave the lymph node in the efferent lymph and eventually rejoin the bloodstream

Question 8

T cells that encounter antigen on APC…

Answer 8

• are activated to proliferated and differentiate into effector cells

Question 9

Effector cells can also leave the lymph node in the…

Answer 9

• efferent lymph and enter the cirsulation

Question 10

Naive T cells can enter lymph nodes int he afferent lymph as well as from the blood. T or F

Answer 10

• T

Question 11

Recirculation of the T cells can occur through two different ways.

Answer 11

• the blood

- through the lymphatic system

Question 12

Activation of naive T cells requires a co-stimulatory signal delivered by the 3 kinds of professional APC found in the secondary lymphoid tissues

Answer 12

• principle co-stimulatory molecules on professional APC are B7 molecules, which bind CD28 proteins on the T-cell surface
• binding of TCR and co-receptor CD4 to the peptide occurs
• this signals clonal expansion of T cells only when the co-stimulatory signal is given by the binding of CD28 to B7
• both CD28 and B7 are members of the immunoglobulin superfamily
• microbial substances induce co-stimulatory activity in macrophages
• in absence of infection, macrophages express no B7 and few MHC molecules

Question 13

3 types of professional APC populate different parts of the…

Answer 13

• lymph node
• dendritic are situated in the T cell areas of the lymph-node cortex
• macrophages are distributed throughout the lymph node
• B cells populate mainly the follicles

Question 14

Proliferation and differentiation of activated T cells are driven by the cytokine _________

Answer 14

• IL-2
• activation by a APC initiates a program of differentiation in the T cell that starts w/ burst of cell division and then leads to the acquisition of effector function
• IL-2 controls this and is synthesizes by the activation of T-cell itself

Question 15

Antigen recognition by a naive T cell in the absence of co-stimulation leads to the T cell becoming nonresponsive. Otherwise called…

Answer 15

• Peripheral tolerance

- (anergic)

Question 16

T-cell tolerance to antigens expressed on nonprofessional APC results from antigen recognition in the absence of co-stimulation. T or F

Answer 16

• T

Question 17

On activation, CD4 T cells acquire distinctive helper functions. There are two types of helper cells:

Answer 17

• Th1: drives cellular mediated immunity
• Th2: drives humoral immunity
• third type of CD4 T cell: regulatory T cell (Treg): regulated Th1 and Th2

Question 18

Naive CD8 T cells are activated to become cytotoxic effector cells in several different ways

Answer 18

• activation of naive CD8 T cells to become cytotoxic effector cells (CTL- cytotoxic T lymphocyte) which generally requires stronger co-stimulatory activity than is needed to activate CD4 T cells
• only dendritic cells, the most potent of the APC, provide sufficient co-stimulation
• when APC offers suboptimal stimulation, CD4 T-helper 1 cells can help out to activate naive CD8 T cells
• activity of IL-2 in the proliferation and differentiation of CD8 T cells to effector cells

Question 19

Effector T-cells responses to infection do not depend on ____________________ signals

Answer 19

• co-stimulatory
• unlike naive T cells, effector T cells can respond without the need for co-stimulatory molecules
• most human cells don’t express the B7 co-stimulatory molecule
• means CD8 cytotoxic T cells can kill any virus-infected cell because of this relaxation in requirement

Question 20

Effector T-cell functions are carried out by ____________ and _____________

Answer 20

• cytokines
• cytotoxins
• the effector T cell produce distinct sets of effector molecules

Question 21

Cytotoxic CD8 T cells are selective and serial killers of target cells at sites of infection

Answer 21

• when cytotoxic T cells recognize specific antigen, the delivery of cytotoxins is aimed directly at the target cell
• effector cytotoxic T cells contain stored lytic granules, which are modified lysosomes contain a mixture of specialized protein called cytotoxins
  1. Granzymes, perforins, granulysin, and serglycin
  2. Producing the Fas ligand

Question 22

Cytotoxic T cells (CD8 T cells) kill their target cells by inducing apoptosis by 2 methods

Answer 22

• lytic granules

Question 23

Th1 CD4 cells induce ____________ to become activated

Answer 23

• macrophages
• principle function of Th1 cells is to help the resident macrophages at the sites of infections become more proficient in the phagocytosis nd killing pathogens
• Th1 cells leave the secondary lymphoid tissue to do this (activate macrophages)

Question 24

Macrophages needed to signals for activation from TH1 cells

Answer 24

• TNF-gamma and CD40 ligand

- TH1 cells coordinate the host response to pathogens that live in macrophages

Question 25

The immune response to intravesicular bacteria is coordinated by activated TH1 cells

Answer 25

• The activation of TH1 cells by infected macrophages results in the synthesis of cytokines that activate the macrophage and coordinate the immune response to intravascular pathogen

Question 26

CD4 TH2 (and TFH) cells activate only those B cells that recognize the same antigen microbe as they do

Answer 26

• main function of TH2 cells are to help B cells mount an antibody response against parasitic infectious agents
• upon interacting with a naive B cell the T cell response by synthesizing CD40 ligand
• B cells have a CD 40 receptor on them
• this cooperation is only effective if the B and T cells are specific for the same antigens

Question 27

Th2 effector (and especially TFH) cells _______ ______ _______ the secondary lymphoid tissue

Answer 27

• do not leave
• the specific interaction of an antigen-binding B cell with a helper TH2 cell leads to the expression of CD40 ligand (CD40L) and the secretion of IL-4, IL-5, and IL-6.
• in concert, these TH2 products drive the proliferation of B cells and their differentiation to form plasma cells dedicated to the secretion of antibody