NK cells

Question 1

How can NK cells distinguish healthy and infected or tumor cells?

Answer 1

By 2 types of receptors, activating and inhibitory.
NK cells express a set of activating receptors that recognize self proteins whose expression is induced by cellular stress: ○ Infections ○ Malignant transformations (tumor) ○ Other stresses

Express another set of of inhibitory receptors that recognize MHC class I molecules (which are present on almost all cell types)

Question 2

Activated NK cells perform
(Kill and produce)

Answer 2

Kill the altered self cell ○ Produce cytokines that induce adaptive response

Question 3

express activating and inhibitory receptors to distinguish between healthy and infected cells

Answer 3

NK cells

Question 4

recognize MHC class I molecules and inhibit signaling by the activating receptors → does not kill normal cells

Answer 4

Inhibitory receptors

Question 5

can overrule the inhibition such as in stressed or altered cells (cancer cells)

when NK kill abnormal cells

Answer 5

up regulation of ligands

Question 6

Alternatively, activation can occur when inhibitory signals are lost, such as when viruses inhibit

Answer 6

MHC class I expression in virus-infected cells or alter its conformation so as to avoid recognition by CD8 T cells

Question 7

What are the mechanisms of NK cells’ cytotoxicity?(2)
Initiated by what? Entrance of cells?

Answer 7

1. Granule-mediated cytotoxicity- initiated by targeted release of lytic granules toward a locally attached target cell
2. Granzymes can then enter the target cell by perforin-pores in the plasma membrane (left) or by endocytosis and perforin-aided escape from endosomes (right) → granzymes induces caspase activation, mitochondrial dysfunction, or caspase-independent apoptosis

Question 8

Granzymes cause

Answer 8

apoptosis

Question 9

Perforin can

Answer 9

open membrane