Natural Born Killers: NK Cells and CD8+ T Lymphocytes

Question 1

Innate and adaptive immunity - define both

Answer 1

Innate: non-specific (or broadly specific), immediate response

Adaptive: highly-specific, delayed response

Question 2

Origin of NK and T cells - compare

Answer 2

Both arise from common lymphoid progenitor cell

Both part of the lymphocyte lineage

Question 3

Role of cytotoxic lymphocytes + what do they require

Answer 3

We need cytotoxic cells as a means to destroy
cells infected with bacteria, viruses or parasites
Tumour cells

This requires a cell-surface mechanism to display what is going on within a cell

Question 4

MHC class I - found where, function and recognised by what

Answer 4

MHC class I proteins are found at the cell surface and form a structure that holds antigenic peptides for surveillance by T cells

MHC-I = recognised by CD8+ cytotoxic T cells

Question 5

Intracellular proteins are presented at

Answer 5

Intracellular proteins are presented at the cell surface by MHC class I

Question 6

MHC class I structure in humans and the distribution

Answer 6

Humans: HLA-A, -B, -C
Tissue distribution: all nucleated cells
two polypeptides, non-covalently bound:

Question 7

MHC class I structure - alpha vs beta2 microglobulin

Answer 7

Alpha chain = 45 kd
Polymorphic
Glycosylated
Inserted in membrane

B = 12kd

and opp. for rest

Question 8

MHC class I proteins are central to anti-viral immune responses, so why don’t we see many pathogens that have mutated to avoid antigen presentation?

Answer 8

Multiple genes (e.g. two copies each of HLA-A, B and C)

High genetic variability within these genes

Question 9

Amino acids in the MHC peptide binding groove create

Answer 9

Amino acids in the MHC peptide binding groove create pockets where the bound peptide can “anchor”

Question 10

MHC-I and MHC-II play a central role in the

Answer 10

MHC-I and MHC-II play a central role in the ability of the immune system to distinguish self from non-self

Question 11

TCR recognise what two things

Answer 11

TCR recognise two things
MHC protein itself (hence compatibility…)
Antigenic peptide presented by MHC protein

Question 12

T cell receptor recognition of MHC - describe

Answer 12

TCR recognises both the MHC protein and the peptide antigen being presented by it

Binds with a diagonal footprint that cuts across both alpha helices with the peptide in between

Question 13

Compare binding sites for CD8 and TCR

Answer 13

CD8 acts as a co-receptor for MHC-I, and is required for the T cell to make an effective response

TCR binds to the α1α2 domains

CD8 binds to the support domains (α3 and β2m)

Similar situation for CD4 and MHC-II

Question 14

List and describe effects of microbes on MHC/TAP

Answer 14

Microbes may subvert MHC upregulation

Inhibit MHC-I transcription (adenovirus)
Block TAP activity (HSV)
Retain MHC-I in endoplasmic reticulum (adenovirus, HCMV)
Target MHC-I for disposal from ER (HCMV)
Downregulate MHC-I from cell surface (HIV)

Question 15

What are NK cells?

Answer 15

Classical NK cells are large granular lymphocytes that are not T or B cells

Question 16

NK cell receptor expression

Answer 16

Do not express T Cell Receptor (CD3) or B cell receptor

Do express the cell surface marker CD56

CD3-CD56+

Question 17

NK cells function

Answer 17

Cytotoxic functions and cytokine secretion

Question 18

Low NK cell activity correlates with

Answer 18

Low NK cell activity correlates with severe disseminating herpesvirus infections

Question 19

Killer Ig-like receptors (KIR) - function

Answer 19

Killer Ig-like receptors (KIR) are innate immune receptors that regulate the activity of Natural Killer cells

Question 20

Leukocyte Ig-like receptors (LILR) - function

Answer 20

Leukocyte Ig-like receptors (LILR) are innate immune receptors that regulate the functions of NK cells

Question 21

KIR and LILR are encoded in a

Answer 21

KIR and LILR are encoded in a gene complex (the leukocyte receptor complex or LRC) on chromosome 19

Question 22

Function of Killer Ig-like receptors (KIR)

Answer 22

When KIR recognise MHC-I they inhibit NK cells from releasing lytic granules

Question 23

Explain the concept of “missing self” in relation to KIR’s

Answer 23

Some viruses down-regulate MHC-I as a means to evade cytotoxic T cells, loss of MHC-I is also a common feature of tumour cells

If a target cell does not express MHC-I then there is no KIR inhibition, lytic granules will be released to lyse the target

Known as “missing self”

Question 24

Killer Ig-like Receptors (KIR) - which face do they bind to and do what

Answer 24

Inhibitory KIR bind to the same face of MHC-I as the T cell receptor

recognise subsets of MHC-I alleles

Question 25

Killer Ig-like Receptors (KIR) - explain disease associations of KIR’s

Answer 25

KIR are also polymorphic, as well as being polymorphic individual KIR genes vary in their presence between individuals

Different MHC-I/KIR combinations show disease associations e.g. in HIV infection

Question 26

Killer Ig-like Receptors (KIR) - list allele specificity

Answer 26

HLA-class I specificity

Question 27

KIR2DL1 - list allele specificity

Answer 27

Group 2 HLA-C alleles expressing Lys80 (such as, HLA-Cw2, -Cw4, -Cw5, -Cw6)

Question 28

KIR2DL2/3 - list allele specificity

Answer 28

Group 1 HLA-C alleles expressing Asn80 (such as HLA-Cw1, -Cw3, -Cw7, -Cw8)

Question 29

KIR3DL1 - list allele specificity

Answer 29

HLA-Bw4 alleles (e.g. HLA-B27)

Question 30

Natural cytotoxicity receptors (NCRs) - function

Answer 30

These provide activating signals to NK cells, but are not well characterised

Question 31

Natural cytotoxicity receptors (NCRs) - compare action of all the types

Answer 31

NCR 1 binds viral hemagglutinin

NCR2 – binds a ligand that is expressed on tumor cells and upregulated by viral infection

Ligand for NCR3 is a stress induced
protein

Question 32

Target cell death or survival depends on

Answer 32

Target cell death or survival depends on balance of activating and inhibitory signals

Question 33

Antibody-dependent cell-mediated cytotoxicity (ADCC) - describe

Answer 33

AB binds AT on target cell surface

Fc receptors on NKC recognize AB

NK signalled to kill target due to FcR cross-linking

=

target cell dies by apoptosis

Question 34

Why do NK cells kill tumour cells?

Answer 34

Similar to many pathogens, tumor cells can escape the adaptive immune system, by downregulating the expression of MHC class I.

This makes them more susceptible to NK cells.

Question 35

Mechanisms of lysis – cytotoxic granules

Answer 35

NK cells and T cells carry granules filled with cytotoxic proteins
Release cytotoxic granules at site of contact with target cell
(must be directed in order to avoid damaging innocent bystander cells)

Question 36

CD8 cells can trigger apoptosis of target through Fas/FasL interaction - describe

Answer 36

This process does not depend on cytotoxic granules

Fas ligand (FasL) on T cells engages Fas on target cells to trigger apoptotic pathway

Fas/FasL triggered apoptosis is used to dispose of unwanted lymphocytes

Question 37

Loss of Fas can result in

Answer 37

Loss of Fas can result in autoimmune lymphoproliferative syndrome (ALPS)

Question 38

NK cell - describe the:

Receptor type
Ligand type
Effect of MHC I absence
Effect of MHC I presence

Answer 38

Receptor type = NKR (activating and inhibitory)

Ligand type = MHC I, MICA/B, immune complexes etc

Effect of MHC I absence = immediate cytotoxicity (‘missing self’)

Effect of MHC I presence = inhibitory signal to NK cell

Question 39

Cytotoxic T cell - describe the:

Receptor type
Ligand type
Effect of MHC I absence
Effect of MHC I presence

Answer 39

Cytotoxic T cell - describe the:

Receptor type = T cell receptor

Ligand type = peptide-MHC I complex

Effect of MHC I absence = lack of recognition

Effect of MHC I presence = TCR engagement

Question 40

CTL cells in terms of:

CD8 use 
Receptor expression
Response to MHC class I
Engaging with target 
Memory

Answer 40

Cytotoxic T cells

CD8 use = Use CD8 as a co-receptor for MHC class I

Receptor expression = Each express a unique receptor with high specificity for a single MHC/peptide complex

Response to MHC class I = Survey MHC class I on the surface of other cells, searching for foreign antigens

Engaging with target = Initial activation of naïve T cells, followed differentiation and proliferation required

Memory = yes

Question 41

NK cells in terms of:

CD8 use 
Receptor expression
Response to MHC class I
Engaging with target 
Memory

Answer 41

CD8 use = Do not use a co-receptor for MHC class I, do not express CD8

Receptor expression = Invariant receptors with broader specificity for MHC allele subsets

Response to MHC class I = Respond to the absence of MHC class I

Engaging with target = Ready to act on encountering targets in the periphery

Memory = No memory