chapter 12

Question 1

What are the 6 antibody-mediated effector functions?

Answer 1

1. Neutralization
2. Agglutination
3. Opsonization
4. Complement Activation
5. Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)
6. Antibody-Dependent Degranulation and Mediator Release

Question 2

protects against viral or bacteria infection or the damaging effects of toxins

Answer 2

neutralization

Question 3

enhances neutralization and more efficient clearance of pathogens form the body

Answer 3

agglutination

Question 4

promotes and/or enhances the engulfment of antigens by phagocytes

Answer 4

opsonization

Question 5

results in the generation of the membrane attack complex (MAC), creating pores in pathogen membranes and killing the microbe

Answer 5

complement activation

Question 6

activates the killing activity of several types of cytotoxic cells, e.g., NK cells

Answer 6

antibody-dependent cell-mediated cytotoxicity (ADCC)

Question 7

triggers mediator release from granulocytes

Answer 7

antibody-dependent degranulation and mediator release

Question 8

Which immunoglobulin has the highest molecular weight?

Answer 8

IgM because it is a pentamer

Question 9

Which antibody is the first produced in a primary response?

Answer 9

IgM

Question 10

describe the effector functions of IgM:

Answer 10

-lower affinity
-pentavalent
-very good at complement fixation leading to MAC formation and target lysis
-efficient at forming dense Ab-pathogen complexes that are efficiently engulfed by macrophage

Question 11

What are the subclasses of IgG and their distinct effector capability?

Answer 11

-Human IgG1/IgG3 effective at complement fixation
– Mouse IgG2a/human IgG1 good at mediating ADCC by NK cells

Question 12

What is the major Ig isotype found in secretions like tears and mucus?

Answer 12

IgA

Question 13

describe the effector functions of IgA:

Answer 13

-effective at neutralizing toxins and pathogens
-does not fix complement, so does not drive inflammation
-long half-life in secretions due to protease-resistant amino
acid sequence in Fc region

Question 14

describe the effector functions of IgE:

Answer 14

-best known for role in allergy and asthma
-may also play a role in protection against parasitic helminths and protozoa
-degranulation of eosinophils/basophils
-release of molecules such as histamine to damage large pathogens

Question 15

what are the 3 subsets of cytotoxic effector cells?

Answer 15

-cytotoxic T lymphocytes
-NK T cells
-NK cells
*these eliminate infected cells and abnormal tumor cells

Question 16

CTLs recognize and kill infected/tumor cells via ___________________

Answer 16

TCR activation

Question 17

CTL signal 1:

Answer 17

TCR binds peptide presented by APC on MHC class I

Question 18

CTL signal 2:

Answer 18

-costimulatory signal transmitted by CD28-B7 (B7-1: CD80, B7-2: CD86) interaction between T cell and APC
– APCs get help from T cells to upregulate stimulation molecules

Question 19

CTL signal 3:

Answer 19

provided by IL-2, inducing proliferation and differentiation into CTL form

Question 20

-4 peptide-bound MHC I molecules bound together and conjugated to a fluorescence marker

Answer 20

MHC tetramers

Question 21

Describe how CTLs can be tracked with tetramers:

Answer 21

-tetramer recognizes CTLs with a TCR capable of binding peptide/tetramer
-flow cytometry is used to detect fluorescent cells
-very sensitive

Question 22

What are the two mechanisms for initiating CTL-mediated apoptotic death of target cells?

Answer 22

1. Directional delivery of cytotoxic proteins (perforin and granzymes) that are released from CTLs and enter target cells.
2. Interaction of the membrane-bound Fas ligand on CTLs with the Fas receptor on the surface of target cells.

Question 23

What is Fas-FasL mediated cytolysis?

Answer 23

• FasL is found on CTLs
• Fas is found on target cell
• Fas bound by FasL initiates a death signal leading to apoptosis

Question 24

Natural killer cells make up 5-10% of what population?

Answer 24

circulating lymphocyte population

Question 25

-non-specific cytotoxicity -the first line of defense against viral infection -Kill virus and other intracellular pathogen-infected cells, and tumor -Produce cytokines to regulate innate and adaptive immunity

Answer 25

natural killer cells

Question 26

How are NK cells different from CTLs?

Answer 26

– No Ag Specific TCR – No MHC restriction – No memory, same intensity regardless of repeated exposure

Question 27

What are candidates for activating signals in the missing self model?

Answer 27

C-type lectins

Question 28

Describe the inhibitory receptors of the missing self model:

Answer 28

– CD94/NKG2 recognize HLA-E * If HLA-E is present - inhibitory signal, no killing * No HLA-E (during viral infection) - no inhibitory signal, killing – KIRs recognize specific MHC molecules - inhibitory signal, no killing

Question 29

Describe the entire process of the missing self model:

Answer 29

-Normal cells present a ligand for the activating (killing) receptor on NK cells AND an MHC class I ligand for the inhibitory receptor -When viruses infect cells, some may inhibit MHC class I expression to evade detection and elimination by CTLs -The balance of inhibitory vs activating signals determines whether NK is activated or not

Question 30

How do NK cells induce apoptosis of their targets?

Answer 30

Once activating signal molecules are engaged, NK cells use mechanisms very similar to CTLs to induce target cell death – Release of perforins/granzymes at junction of two cells

Question 31

Describe the nature of NK cells:

Answer 31

-large granular lymphocytes -lack T cell receptor, CD3 proteins, and surface IgM and IgD -thymus not required for development -normal numbers in SCID patients

Question 32

What are the many functions of NK cells?

Answer 32

-kill virus infected cells and cancer cells (nonspecific) -killing is not dependent on foreign antigen presentation by Class I or II MHC proteins -killing is activated by failure of a cell to present self antigen in association with Class I MHC proteins or by a reduction in the number of Class 1 MHC proteins on the cell surface -kill by producing perforins and granzymes, which causes apoptosis of target cell

Question 33

NKT cells bridge ______________________immune systems.

Answer 33

innate/adaptive

Question 34

What does the TCR of NKT cells recognize?

Answer 34

glycolipids presented by nonpolymorphic CD1d

Question 35

Describe NKT cells:

Answer 35

Can act as helper cells (secreting cytokines) or killer cells – Killing seems dependent on Fas-FasL interactions * Include both CD4+ and CD4– cell types * Don’t form memory cells * Possess NK surface proteins rather than T-cell varieties