Lecture 14 - NK cells, innate lymphoid cells & innate-like lymphoid cells

Question 1

Myeloid vs lymphoid cells: what part of the immune system are they involved in and what are examples of cells belonging to each type?

Answer 1

Myeloid cells - innate immunity:
* Dendritic cells
* Macrophages
* Monocytes
* Neutrophils
* Basophils
* Eosinophils
* Mast cells
* NK cells
* Innate lymphoid cells

Lymphoid cells - adaptive immunity:
* T-cells
* B-cells
* NK-cells
* Innate lymphoid cells

Question 2

ILCs: what are they, what do they do, where are they located, and what are the types?

Answer 2

Innate lymphoid cells

• Produce cytokines to induce immunity and inflammation
• Interact with surrounding non-immune cells - ie increasing barrier integrity, increasing mucus production, etc

Enriched at barrier sites and associated lymphoid tissue

• Helper-like ILCs (ILC1, 2, 3, etc) - reflect Th cells (ILC1 = Th1 cells)
• Killer ILCs (NK cells) - reflect cytotoxic CD8+ t-cells

Question 3

ILC1: what does it help defend against, what TF does it express, and what cytokines does it produce?

Answer 3

Intracellular virus/bacteria - produces cytokines to aid killing by macrophages and other innate cells

Express T-bet

• IFN-γ and TNF-α during early stages of infection
• IL-12
• IL-18

Question 4

ILC2: what does it help defend against, what TF does it express, what does it recognise for activation, and what cytokines does it produce?

Answer 4

Helminths - produces cytokines to aid killing by macrophages and other innate cells

Express GATA3

Recognise DAMPS - IL-25, IL-33, TSLP produced by stressed/damaged cells

• IL-4
• IL-5
• IL-13

Question 5

ILC3: what does it help defend against, what TF does it express, what cytokines is it activated by, what cytokines does it produce, and what types of ILC3 are there?

Answer 5

Extracellular bacteria/fungi - produces cytokines to aid killing by macrophages and other innate cells

RORγt (innate equivalent of Th17)

IL-1b
IL-23

• IL-17A
• IL-22

Contain two main subsets:
* Lymphoid tissue-inducer cells
* Natural cytotoxicity receptor positive (NCR+) ILC3

• Also contain a Bcl6+, acting as a Tfh cell mirror

Question 6

ILCreg: what lymphoid cell does it mirror and what TF and cytokines does it express?

Answer 6

Treg

TF - Foxp3
Cytokine - IL-10

Question 7

IL-17A

Answer 7

Acts to attract neutrophils

Question 8

IL-22

Answer 8

Acts on epithelial cells to induce secretion of antimicrobial peptides, reinforce barrier function

Question 9

LTi cells: what are they, what do they do, and what is their Th17 equivalent?

Answer 9

(NCR-) lymphoid tissue inducer cells

• Critical for the development of lymph nodes and secondary lymphoid structures (e.g. Peyer’s patches) in the fetus
• Help to form intestinal lymphoid structures in adults known as cryptopatches and isolated lymphoid follicles

Function is unique to ILC3 - not found in equivalent Th17 cells

Question 10

NCR+ ILC3: what is it, what cell surface proteins does it express, what cytokines does it produce, and what TF does it express?

Answer 10

Natural cytotoxicity receptor-positive innate lymphoid cell group 3 - ILC NK cel;ls (NK-22)

Express NKp44, NKp46, and NCAM-1/CD56

Primary source of IL-22 also produces IFN-γ

Express T-bet

(ER)

Question 11

NK cells: what type of ILCs are NK cells and how prevalent are NK cells in the general ILC population?

Answer 11

NCR+ - natural cytotoxicity receptor + (NK)
NCR- - natural cytotoxicity receptor - (not an NK)

~70% of the intestinal ILCs are NCR+, and 15% are NCR-

Question 12

ILCs: what survival signals do they require and how do they become activated?

Answer 12

Common gamma chain cytokines:
* IL-2
* IL-7
* IL-15 (NK cells)

• Recognise DAMPS - IL-25, IL-33, TSLP
• Activated by PAMP recognising cells, IL

Question 13

NK cells: what are they, what do they do, how do they know what cells to not kill, what inhibitory signals do they receive, how do they kill cells, and what receptor types are there?

Answer 13

Natural killer cells

Monitor for ‘altered-self’ - defence mechanism against cancer cells

Surveillance monitoring of MHC-I expression

Inhibitory interactions between CD94/NKG2A on the NK cell with regions of MHC-I

• Lack of inhibitory signalling
• NK cell activation
• Killing of target cell - using perforin and granzymes
• KIRs
• KLRs

Question 14

NK cell activation: when are activating signals presented for these cells?

Answer 14

Stressed cells (infected, damaged, etc) upregulate activating receptor ligands and tip balance towards killing, even despite presence of “self-signals” from MHC-I

Question 15

KIRs: what are they, where are they encoded, are they present in mice, what complex is it a part of, and how do they convert their signalling?

Answer 15

Killer immunoglobulin-like receptors

Encoded on human chromosome 19

No, but they have the functionally equivalent Ly48 which shows the necessity of these structures (convergent evolution)

Leucocyte receptor complex (LRC)

ITAMs and ITIMs

Question 16

KLRs: what are they, where are they encoded, what complex is it a part of, and how do they convert their signalling?

Answer 16

Killer lectin-like receptors

Encoded on human chromosome 12

Natural killer gene complex (NKC)

ITAMs and ITIMs

Question 17

LRC: what is it and what does it do?

Answer 17

Leucocyte receptor complex

Encodes a large number of immunoglobulin (Ig)-like receptors involved in the immune response, particularly in modulating natural killer (NK) cell function

Question 18

NKC: what is it and what does it do?

Answer 18

Natural killer gene complex

Encodes proteins, some of which are structurally unrelated, that impact on NK-cell function

Question 19

Ig-like receptors: what are they and what do they do?

Answer 19

Immunoglobulin-like proteins that contain motifs similar to antibodies

Involved in mediating cell-cell contact and recognition of other proteins, adhesion between cells, and regulating permeability and trafficking of leukocytes

Question 20

Ig-like molecules: what are they and what do they do?

Answer 20

Immunoglobulin-like proteins

Act as receptors and ligands to connect with complementary structures - crucial for cell life, cell-to-cell connections and interactions over the intercellular matrix

Question 21

NK activation: what is the pathway?

Answer 21

• Activating receptors (KiRs, etc) associate with accessory molecules such as DAP12 which contain ITAMs
• Ligand engagement causes phosphorylation of the ITAM Tyr residue
• Activated ITAMs trigger signal transduction leading to NK activation

Question 22

ITAMs: what are they, where are they found, and what do they do?

Answer 22

immunoreceptor tyrosin-based activatory motifs

Found in the cytoplasmic tails of receptors

Signal transduction - activating signal

Question 23

NK cell inhibition: what is the pathway?

Answer 23

• Inhibitory receptors have long cytoplasmic tails which contain ITIMs
• Ligand engagement causes phosphorylation of the ITIM Tyr residue
• Phosphorylated ITIMs recruit phosphatases that interfere with and supress signals that would otherwise have led to activation

Question 24

ITIMs: what are they, where are they found, and what do they do?

Answer 24

immunoreceptor tyrosine-based inhibitory motifs (ITIMs)

Found in the cytoplasmic tails of receptors

Signal transduction - inhibitory signals

Question 25

ILLCs: what are they, how do they differ from ILCs, how do they differ from adaptive immune cells, what do they do, and what are examples of these cells?

Answer 25

Innate-like lymphoid cells

• Express a restricted form of the T cell-receptor

They have only a limited and restricted repertoire of antigen recognition

Produce cytokine without the need for clonal expansion and polarization

• NKT cells
• γδ T cells
• MAIT cells

Question 26

iNKT: what are they, what do they do, how are they boosted, how do they form memory responses, and do they have subsets?

Answer 26

Invariant NKT cells

Express an invariant αβ TCR that recognises lipid antigens presented by the MHC-like molecule CD1d on APCs - can then produce cytokines, boost/regulate immune responses, and kill cells (perforin/granzymes)

Like other innate lymphocytes, cannot be boosted or form a memory response

Come in different subsets (just like T helper cells and ILCs) (ER)

Question 27

γδ T-cells: what are they, where are they produced, and when are they first produced?

Answer 27

The 5% of T-cells that instead contain a γδ chain instead of the usual αβ chains

Arise from the same progenitor as αβ T cells in the thymus

Amongst the first T cells generated in embryos where they seed barrier tissues (skin, lung, gut, uterus) and remain there

Question 28

γδ T cells: what subsets are produced prior to birth, do they produce cytokines, why are they considered innate, how are they boosted, how do they form memory, and what types of antigens do they recognise?

Answer 28

Multiple subsets, but characteristic Vγ chain usage

Certain types of γδ T cell have restricted cytokine producing ability (e.g. Vγ6 produce IL-17 and are also known as γδ17 cells)

Have restricted TCR chain and respond rapidly without need for proliferation and polarization

Also cannot be boosted or form memory

• Lipids presented on CD1 class molecules
• Phosphoantigens - including those produced by bacteria (e.g. HMBPP)
• Butyrophilin molecules that regulate γδ T cells in tissues (e.g. skin, gut)
• MHC-like stress ligands (similar to NK cells) - NOT MHC most of the time, MHC is adaptive

Question 29

Why is our immune system so convoluted?

Answer 29

The immune system contains many cell types that appear to perform similar functions (e.g. Th cells, ILCs, iNKT cells, γδ T cells)

WHY:
* Convergent evolution driven by different environmental pressures (e.g. different pathogens in different tissues)?
* Evolutionary arms race?Pathogens evolve quickly too - need to have multiple systems to make ensure survival if one response fails
* Timing: ILCs respond quickly without need for antigen to ensure host survives
* Energy saving? iNKT cells & γδ T cells - ability to respond to rapidly to specific common antigens without the need for an adaptive response
* Variety: Ability to respond to certain non-protein antigen types (e.g. lipids, phosphoantigens) not recognised by adaptive immune cells via MHCI/MHCII

All systems maintain some unique functions too (e.g. lymphoid tissue formation).

Question 30

MAIT cells: what are they and what do they do?

Answer 30

Mucosal-associated invariant T (MAIT) cells - innate t-cells that have been evolutionary conserved

• Defence against bacterial and viral infections - recognise vitamin B derived ligands
• Tissue repair
• Tumor immunology

Question 31

What else do ILCs do? (ER)