module 07 section 02 (antigen-nonspecific CMI)

Question 1

the primary role of macrophages during the inital cell-mediated response is?

Answer 1

phagocytosis

Question 2

what are the roles of ROI, NO and lysosomal enzymes (produced by macrophages) in cell-mediated immunity?

Answer 2

killing microbes in phagolysosomes

Question 3

what is the role of cytokines (secreted by macrophages) in cell-mediated immunity?

Answer 3

TNF, IL-1: leukocyte recruitment (inflammation)

IL-12: Th1 differentiation and IFN-y production

Question 4

what is the role of increased expression of B7 costimulators and MHC molecules (by macrophages) in cell-mediated immunity?

Answer 4

increased T-cell activation (amplification)

Question 5

recall: what is the effect of IL-12 on naive T-cells?

Answer 5

• induces the differentiation of naive CD4 Th0 cells into Th1 cells
• in the later stages of cell-mediated immunity, Th1 cells wil stimulate macrophages to continue their effector functions through the production of cytokines

Question 6

what receptors are present on NK cells? what do they recognize?

Answer 6

• killer inhibitory receptors (KIRs)

- recognize self MHC class I

Question 7

how do KIRs work?

Answer 7

• all normal host cells express MHC class I molecules, so when KIRs recognize these there’s no killing of normal cells
• virally infected cells have downregulated expression of MHC class I molecules, so KIRs are not engaged, resuling in signalling the NK cell to kill the cell

Question 8

what is another mechanism (other than KIRs) that NK cells interact with and kill target cells?

Answer 8

antibody-dependent cell-mediated cytotoxicity

Question 9

list the 3 steps of antibody-dependent cell-mediated cytotoxicity

Answer 9

(1) antibody opsonization
(2) NK cell-FcyRIII (CD16)
(2) activated NK cell

Question 10

explain antibody opsonization

Answer 10

• infected target cells express pathogen antigens on their cell surface
• these cells are recognized by specific antibodies produced by antibody-secreting plasma cells
• the anitgens are then marked to be recognized and eliminated by phagocytes

Question 11

what is FcyRIII (or CD16)?

Answer 11

receptors expressed by NK cells

Question 12

explain the role of FcyRIII in antibody-dependent cell-mediated cytotoxicity

Answer 12

• these receptors recognize and bind the Fc portion of antibodies
• once it binds an anitbody attached to a target cell, the NK cell is activated

Question 13

explain the role of activated Nk cells in antibody-dependent cell-mediated cytotoxicity

Answer 13

activated NK cells bound to a target release the content of their cytolytic granules by directly killing the target cell or by inducing FasL/Fas-mediated apoptosis

Question 14

what is FasL/Fas-mediated apoptosis?

Answer 14

Fas and its ligand FasL are cell surface proteins that (when cross-linked) trigger a cascade of events that result in apoptosis of the target cell