Cell Mediated Immunity

Question 1

What do CD4+ cells do?

Answer 1

Secrete cytokines to help other immune cells gain functional ability.

Question 2

What do CD8+ cells do?

Answer 2

CTL. Kill infected cells, tumor cells, and sometimes even healthy cells in an autoimmune response.

Question 3

How are naive T cells activated?

Answer 3

Activated by pAPC (macrophages, DC, active B cells). DCs activate naive T cells most efficiently due to their high levels of costimulators.

Question 4

What are the functions of cell adhesion molecules in immunity? What is an example of a cell adhesion molecule?

Answer 4

They glue t-cells and APC’s together so that TCRs can sample everything sufficiently. CD58 (on APC) and CD2 (on T cell).

Question 5

What molecules give T cells signal 2?

Answer 5

B7 (on APC) and CD28 (on T cell). Also, CD40 (on APC), and CD40L (on T cell).

Question 6

CTLA4

Answer 6

Can also bind to B7 on APCs with a higher affinity than CD28. Provides a suppressive signal to ensure proper T cell regulation. Gets upregulated when B7 binds to CD28.

Question 7

Where does T Cell activation occur?

Answer 7

Lymphoid organs, then they migrate to the site of infection.

Question 8

What happens if a T cell receives signal 1, but not signal 2?

Answer 8

Anergy, a state of partial paralysis, occurs.

Question 9

CD40 and CD40L

Answer 9

Costimulatory molecules that activate APC’s to continue activating T Cells (through cytokine release, upregulation of B7, etc.)

Question 10

What is signal 3?

Answer 10

Cytokines secreted following the delivery of signals 1 and 2 that determine the effector response.

Question 11

Why are DC’s such powerful APCs?

Answer 11

Because they have a lot of costimulatory molecules.

Question 12

TCR structure

Answer 12

Alpha and Beta chains, which, when bound, induce activation of the CD3 complex, a series of proteins that propagates the activation signals. CD3 complex also serves as a marker of mature T cells.

Question 13

Marker of mature T cells?

Answer 13

CD3 complex

Question 14

How do CD4 and CD8 participate in T Cell activation?

Answer 14

They stabilize the binding of the MHC to the TCR, and can stimulate ITAM phosphorylation which upregulates effector genes.

Question 15

What happens when a CD4 cell is activated by signals 1 and 2?

Answer 15

It creates Th Cell that upregulates IL2R and releases IL-2, which causes clonal expansion of both CD4 and CD8 cells.

Question 16

Th1 Cells

Answer 16

Secrete IL-2 and IFN-Gamma after signals 1 and 2 (MHC and CD40), promoting macrophage activation, T cell proliferation, antibody production.

Question 17

IL-2

Answer 17

Induces T-cell proliferation. Released from Th1 cells.

Question 18

IFN Gamma

Answer 18

Released from Th1 cells. Activates pAPCs by increasing expression of MHC and B7. This will activate both CTLs and Ths. Stimulates intra-APC destruction of pathogens. Also, helps B cells make antibodies, specifically IgG, which promote complement binding and opsonization.

Question 19

Th2 Cells

Answer 19

Secrete IL4 and IL5. Involved in allergy and helminth attack.

Question 20

IL-4

Answer 20

Induces production of IgE antibodies that mediate allergic responses.

Question 21

IL-5

Answer 21

Activates eosinophils involved in allergy.

Question 22

Th17 Cells

Answer 22

Secrete IL-17.

Question 23

IL-17

Answer 23

Induce inflammatory response by activating neutrophils, promote secretion of defensins, and increase epithelial barriers.

Question 24

Treg Cells

Answer 24

Suppress T cell responses by secreting TGF B and IL-10.

Question 25

IL-10 and TGFß

Answer 25

Suppressive cytokines for T cells.

Question 26

Immunological Tolerance

Answer 26

Unresponsiveness to an antigen induced by exposure of lymphocytes to that antigen.

Question 27

Central Tolerance

Answer 27

Immature, self-reactive T cells undergo negative selection in the Thymus.

Question 28

Peripheral Tolerance

Answer 28

Mature self-reactive T Cells that escape central tolerance and recognize self antigens can become anergic, can be killed, or suppressed. Occurs when signal 2 is absent.

Question 29

IL-1, TNF

Answer 29

Pro-inflammatory cytokines released from macrophages after activation via IFN gamma from Th1 Cells.

Question 30

How do Th1 and Th2 cells interact?

Answer 30

Their responses inhibit each other.

Question 31

How do Th1 cells directly and indirectly stimulate CTL activation?

Answer 31

Directly by releasing pro-CTL cytokines. Indirectly by increasing costimulators on pAPCs, which will then be more effective at activating CTLs.

Question 32

How do CTLs kill infected cells?

Answer 32

Activated CTLs can recognize any cell that expresses MHC class 1, even without costimulators like B7 and CD40. CTL will bind and release perforin and serine esterase granules. CTL detaches and target cell slowly dies.

Question 33

After CTL attack, do target cells die immediately?

Answer 33

No serine esterase and perforin take some time to kill the cell.

Question 34

How are CTLs deactivated?

Answer 34

By CTLA-4 on pAPCs.