Lecture 9

Question 1

What are the 2 major populations of T cells mediate cellular immunity?

Answer 1

CD4 cells (helper T cells) and CD8 cells (cytotoxic cells) that destroys cells harboring foreign antigens

Question 2

T cells are best suited for _____________, and target: (3)

Answer 2

cell-to-cell interactions;
Cells infected with viruses, bacteria, or intracellular parasites, Abnormal or cancerous cells, Cells of infused or transplanted foreign tissue

Question 3

What are the basic steps of cell-mediated immunity?

Answer 3

1. Recognition of antigen presented by an antigen-presenting cell by T cell receptors (TCR’s)
2. Co-stimulation of the T cell
3. Production of a clone of identical effector T cells capable of recognizing initial activator (antigen)
4. Elimination of the foreign intruder

Question 4

Describe antigen binding (step1)
How is TCRs activated?

Answer 4

Mobile APCs (Langerhans/dendritic cells) alert the body to the presence of antigen by migrating to the lymph nodes and presenting antigen.
T cell antigen receptors (TCRs) are activated by binding to an antigen-MHC protein complex.

Question 5

In MHC restriction, what does Tc and TH bind to?

Answer 5

Tc binds to endogenous antigens complexed with class I MHC.
TH binds to exogenous antigens complexed with class II MHC.

Question 6

Class I MHC proteins are found where? Recognized by what?

Answer 6

Found on all cells, except RBCs; Always recognized by cytotoxic TC cells (CD8)

Question 7

Endogenous proteins are… (4)
Degraded by…
Transported into…
Loaded onto…
Displayed on…

Answer 7

Degraded by proteases.
Transported into the ER via TAP (Transporter associated with Antigen Processing).
Loaded onto class I MHC molecules.
Displayed on the cell surface in association with a class I MHC molecule.

Question 8

Describe Class II MHC proteins are found where? Synthesized where?

Where are they inserted and loaded onto?

Answer 8

Found only on mature B cells, some T cells, and APCs; Synthesized in the ER;

Inserted into the phagosomes where the antigen is degraded and the invariant chain is removed for peptide loading. Then, the loaded class II MHC molecules are moved to the cell membrane and display antigenic peptide for recognition by CD4 TH cells.

Question 9

What happens in co-stimulation of T Cell activation? What is a crucial co-stimulatory signal?
After, cytokines like ___ & ___ stimulate proliferation and differentiation of T cells.

Answer 9

T cells must bind to other surface receptors on an APC
B7 binding with the CD28 receptor on the surface of T cells is a crucial co-stimulatory signal

IL-1, 2

Question 10

Without co-stimulation, T cells become…

Answer 10

Become tolerant/respond to that antigen (anergy), are unable to divide and do not secrete cytokines.

Question 11

Helper T cells are __________ cells that play a central role in the ______________.
Once primed by _________________ of antigen, they:
chemically or directly stimulate __________ of other __ cells.
OR
Stimulate __ cells that have already become bound to __________.

Answer 11

regulatory; immune response;

APC presentation;

proliferation; T

B; antigen

Question 12

There is no immune response without _________.

Answer 12

Helper T cells

Question 13

Helper T cells (TH) cells interact directly with __ cells that have antigen fragments on their surfaces bound to ______ receptors.

TH cells stimulate _____ to divide more rapidly and begin ___________.

B cells may be activated without TH cells by binding to ___________________.

Most antigens, require ____________ to activate B cells.

Cytokines released by TH amplify ________________.

Answer 13

B; MHC II

B cell; antibody formation

T cell–independent antigens

TH co-stimulation

nonspecific defenses

Question 14

Cytotoxic T cell (TC cells), or _________, are the only T cells that can directly ________ and ____ other cells.

They circulate throughout the body in search of _________ that display the _______ to which they have been sensitized.

Their targets include: (4)

Answer 14

killer T cells; attack; kill

body cells; antigen

Virus-infected cells
Cells with intracellular bacteria or parasites
Cancer cells
Foreign cells from blood transfusions or transplants

Question 15

Cytotoxic T cells bind to __________ complexes on all ___ cells.

Infected or abnormal cells can be destroyed as long as appropriate antigen and ____________ (e.g., ____) are present.

Answer 15

self-antiself; body

co-stimulatory stimuli; IL-2

Question 16

Natural killer cells activate their killing machinery when they bind to _____________.

MICA receptor is a ____-related cell surface protein in cancer cells, ______-infected cells, and cells of _____________.

Answer 16

MICA receptor

MHC; virus; transplanted organs

Question 17

The mechanisms of Tc action includes Tc cells to bind to the target cell and release ________ into its ________.
In the presence of ____, perforin causes _______ by creating _____________.

Answer 17

perforin; membrane; Ca2+; cell lysis; transmembrane pores

Question 18

During Cell-Mediated Immunity, the primary ____ response peaks within a _____ after signal exposure.

T cells then undergo _________ between days __ and __.

Effector activity wanes as the amount of antigen ________.

The disposal of activated ____________ is a ________ mechanism for the body.

Memory T cells remain and mediate _______________ to the same ________.

Answer 18

T cell; week

apoptosis; 7; 30

declines

effector cells; protective

secondary responses; antigen

Question 19

Other Tc cells induce cell death by:
Secreting __________, which fragments the target cell’s ____.
OR
Secreting _____________, which stimulates _________ by _________.

Answer 19

lymphotoxin; DNA

gamma interferon; phagocytosis; macrophages

Question 20

Suppressor T cells (TS) are __________ cells that release _______, which suppress the activity of both __ cells and __ cells.

Answer 20

regulatory; cytokines; T; B

Question 21

What is the importance of cell mediated immunity?

Answer 21

Since antibodies are useless against intracellular antigens, cell-mediated immunity is needed.

Question 22

What are MHC proteins? When are they ignored?

Answer 22

Antigen holders that comprise the self antigen that indicate the presence of intracellular infectious microorganisms when complexed with endogenous or exogenous antigenic peptides; Ignored by T cells if they are loaded with self protein fragments.

Question 23

What is the significance of MHC molecules.
Why is MHC restricted antigen presentation essential?

Answer 23

Help distinguish between self and non-self. Acting as “antigen holders,” they present peptide fragments on cell surfaces to signal the presence of pathogens or abnormal cells. MHC-restricted antigen presentation is essential for activating T cells only when a true threat is detected, ensuring precise immune responses while preventing inappropriate reactions against the body’s own cells.