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Immunology 436 > Chapter 4 Pt II T Cell Activation > Flashcards

Chapter 4 Pt II T Cell Activation Flashcards

1
Q

What are the two steps to naive T cell activation?

A
  1. Antigen binding
  2. Co-stimulation
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2
Q

Describe co-stimulation. What happens if there is no co-stimulation?

A

Happens to only inactivated/naive T cells. Two signals are given to T cell. First signal is antigen-MHC binding to TCR. Second signal is the B7 (expressed on DC and macrophages) proteins interacting with CD28 on T cell surface. If no co-stimulation, meaning only 1 signal is received, then anergy results, meaning lack of immunity.

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3
Q

Which cytokines trigger proliferation and differentiation of T cell?

A

IL-1 and IL-2 from APCs or other T cells

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4
Q

What happens when anergy occurs?

A

Lack of immunity:
-tolerance to antigen
-unable to divide
-no cytokine secretion

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5
Q

What do activated T cells do?

A

-Enlarge and proliferate in response to cytokines
-Differentiate and perform functions according to T cell class

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6
Q

Describe steps of clonal selection/activation of T cells

A
  1. DC or macrophage phagocytoses antigen and presents fragments to naive T cell
  2. T cell recognizes antigen-MHC complex and TCR/CD4 or 8 proteins bind antigen-MHC complex. Also, co-stimulators molecules bind
  3. Clone formation: activated T cells become memory and effector cells
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7
Q

Primary T cell response peaks within a _____.

A

Week

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8
Q

T cell apoptosis occurs between _____ and ____ days

A

7 and 30 days

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9
Q

Why do T cells apoptose after 1 week to 1 month?

A

Because activated T cells are hazardous if around too long. They produce a large amount of inflammatory cytokines, which leads to hyperplasia (too much proliferation) or cancer

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10
Q

Are B cells hazardous?

A

No, they stay in body for long amounts of time. So, they last longer than T cells

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11
Q

T cell effector activity wanes when?

A

Amount of antigen declines

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12
Q

What are the fates of effector and memory T cells as antigen wanes?

A

Effector activity declines and eventually T cells apoptose
Memory cells remain and mediate secondary response

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13
Q

Helper T cells activate which parts of adaptive immunity?

A

Both humoral and cellular arms

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14
Q

Without helper T cells _______

A

There is no immune response

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15
Q

What do helper T cells help to do?

A

-activate T and B cells
-Induce T and B cell proliferation
-secrete cytokines to recruit other immune cells
-amplify innate defenses (activate macrophages, mobilizes lymphocytes and macrophages, attract other types of WBCs)

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16
Q

Why is there no co-stimulators protein on Th cell activating B cell?

A

Because helper T cell is already activated. Co-stimulation only happens to naive/inactivated T cells

17
Q

Do B cells necessarily need helper T cells to become activated?

A

No, they can be activated by binding T cell-independent antigens. Their response is weak and short-lived. However, most antigens need helper T cell co-stimulation to activated B cells

18
Q

Describe B cell activation by helper T cell

A
  1. Helper T cell binds with antigen displayed on MHCII
  2. Helper T cell releases IL-4 and other cytokines as co-stimulators signals to complete activation
19
Q

Cytotoxic T cells require which cell for activation? How does this cell help?

A

Helper T cells, which cause DCs to express co-stimulators molecules required for CD8 activation

20
Q

Describe CD8 cell activation

A
  1. Helper T cell binds DC
  2. Helper T cell stimulates it to express co-stimulators molecules
  3. DC activates CD8 cell while helper T cell secretes IL-2 to further help activation

*Note that helper T cell binds MHCII on DC while CD8 binds MHCI on same APC

21
Q

List and describe the subsets of helper T cells

A

-TH1: mediate most aspects of cellular immunity
-TH2: defend against parasitic worms and mobilize eosinophils, promote allergies
-TH17: link adaptive and innate immunity by release in IL-17, may play role in autoimmune disease

22
Q

Where to activated cytotoxic T cells reside?

A

Circulate in blood, lymph, and lymphoid organs

23
Q

Targets of cytotoxic T cells?

A

-virus-infected cells
-cells with intracellular bacteria/parasites
-cancer cells
-foreign cells from transfusions or transplants

24
Q

Two methods of direct killing by cytotoxic T cells?

A
  1. Exocytose perforins to create pores, also exocytose granzymes to enter pores and stimulate apoptosis
  2. T cell binds receptor on target cell and stimulates apoptosis
25
Q

how do granzymes trigger apoptosis?

A

By activating enzymes that trigger apoptosis

26
Q

Describe T reg function

A

-reduce immune response by direct cell contact or releasing inhibitory cytokines (IL-10 and TGF-beta)
-prevents autoimmunity by suppressing lymphocytes in periphery. Can induce tolerance to transplanted tissue

27
Q

Together, which two cell types launch direct attack on Ag?

A

Effector T cells and non-specific killers (macrophages and NK cells)

28
Q

What does TGF-beta stand for?

A

Transforming growth factor beta

29
Q

Define cross-reactivity

A

When two antigens appear similar to immune system such that same Ab bind to both

30
Q

Why can tetanus toxoid be used to immunize?

A

Because it cross-reacts with its toxin

31
Q

How much tetanus toxin kills a mouse? How much toxoid required for immunization?

A

10^-12 g to kill mouse
10^-6 for immunization

32
Q

Human blood group A cross-reacts with antiserum against ____ or ____

A

Streptococcus capsule
Influenza virus

33
Q

Human blood group B cross reacts to serum against _____

A

E.coli

34
Q

What are adjuvants used for? Examples?

A

To enhance immune response to immunogen. Example is aluminum potassium sulfate (alum) in USA. Causes immunogen to precipitate resulting in slow time-release so that immune system can develop memory and phagocytose easier

35
Q

Adjuvants used in USA? Europe? Animals?

A

USA = alum
Europe = BCG (bacille Calmette-Guerin) as TB vax. Contains attenuated M. Boris, Corynebacterium, and Bordetella pertussis. Good at activating macrophages to phagocytose and present to T cells
Animals = Freund’s complete adjuvant that has killed Mtb

Immunology 436 (11 decks)

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