Unconventional T cells

Question 1

Describe the main difference between group 1 and 2 CD1 proteins

Answer 1

Group 1 (CD1 A, B, C) are involved in the activation of T cell mediated responses. Group 2 (CD1 D) is involved in innate-like responses by priming iNKT responses.

Question 2

What type of ligand is loaded and presented by CD1 proteins?

Answer 2

Glygolypids, with the sugar being the portion recognized by the TCR

Question 3

Which conventional antigen-presenting molecule do CD1s resemble the most and why?

Answer 3

They are much more similar to MHC II. They present exogenous antigens, their expression is restricted to specific cell types, require lysosomal/endosomal acidification to present the peptide, have no requirement for TAP proteins to transport and load the peptide.

Similarities with MHC I: homodimer with beta2 microglobulin association

Unique feature: monomorphic.

Question 4

What molecule increases the solubility of lipids in intracellular compartments?

Answer 4

MTP

Question 5

Why is there a need for 5 different CD1s? Describe similarities and differences between the different CD1s

Answer 5

There is a need for 5 different CD1s because each of them loads lipids of different complexity given that they all migrate to different compartments in the endolysosomal pathway. They all have similar structures but the shape and size of the loading grooves differ between them.

Question 6

Describe the process of self-potentiation mediated by group 1 CD1s

Answer 6

A DC gets infected (i.e. Mtb infection) and presents a pathogenic lipid on CD1s to a T cell=> T cell mediated cytotoxicity + secretion of antimicrobial mediators. The DC can simultaneously present endogenous self-lipids to an autoreactive T cell=> T cell mediated cytotoxicity + release of antimicrobial mediators (augmentation of the response).

Question 7

How do you identify CD1 restricted T cells from a larger population?

Answer 7

Tetramers of CD1 molecules ligated to a fluorescently labelled molecule

Question 8

Which CD1 molecules get preferentially recognized by alpha/beta and gamma/delta T cells?

Answer 8

ab=> CD1a

yd=> CD1c

Question 9

Describe the role of CD1-restricted T cells in autoimmunity and regulation

Answer 9

self-lipids that stimulate a Th2 response lead to immunoregulation; self-lipids that stimulate a Th1/Th17 response lead to pathogenic T cells that can stimulate the production of autoantibodies.

Question 10

How are immunostimulatory self lipids produced?

Answer 10

They can be produced from inhibitory self-lipids by the action of phospholipase enzymes (endogenous or exogenous)

Question 11

How diverse/restricted is the TCR on innate-like lymphoid cells

Answer 11

The alpha chain is heavily restricted (AV1-2-AJ33 being the most common). The beta chain is also restricted to a relatively low number of recombination events, but it offers more diversity compared to the alpha chain (lecture 2, Dr. Salio, slide 5 on deep sequencing analysis).

Question 12

Describe the key features of iNKT cells

Answer 12

Semi invariant TCR with identical CDR3a
Restricted by CD1d
Recognize glycolipids
Secrete IFN-y and IL-4 (Th1 vs Th2)
Can develop a memory-like phenotype

Question 13

What is the most common ligand of iNKTs?

Answer 13

aGalCer

Question 14

Describe the key features of MAIT cells

Answer 14

Semi invariant TCR
MR1-restricted
Mostly CD8+

Question 15

Which ligands are immunostimulatory and immunoinhibitory for MAITs

Answer 15

Vitamin B2 derivatives are immunostimulatory

Vitamin B9 derivatives are immunoinhibitory

Question 16

Describe the MR1 antigen presentation pathway

Answer 16

Resembles the MHC I pathway. Vitamin B2/9 can either be taken up by the surrounding environment or be produced by intracellular pathogens. They get loaded on MR1 expressed in the ER=> conformational change=> “On” conformation=> secreted in vesicles to the cell surface.

Question 17

Briefly describe the development of iNKTs and MAITs

Answer 17

Both develop in the thymus by interacting with Haematopoietic cells. Microbial metabolites are also required for thymic MAITs development.
MAITs complete their development in the periphery; require interactions with microbial flora and B cells

Question 18

Describe different iNKT subsets.

Answer 18

type 1 iNKT=> low expression of PLZF (+ T-bet)
type 2=> high expression of PLZF (+ GATA3)
type 3=> intermediate expression of PLZF (+ RORyT)
Regulatory subset also recently descovered.

Question 19

Describe the main functions of iNKTs and MAITs

Answer 19

iNKTs: anti-microbial/viral; control incidence of diabetes, anti-tumoral.

MAITs: same as iNKT but seem to a poorer prognostic factor in tumour growth. They also have tissue repair potential.

Question 20

How are MAITs and iNKTs activated.

Answer 20

They can be activated both by immunostimulatory cytokines or by TCR/ pathogenic-ligand interactions.

Question 21

where are gamma-delta T cells localized?

Answer 21

They are localized to tissues

Question 22

Do gamma delta T cells migrate to LNs following maturation in the thymus

Answer 22

No

Question 23

Does the yd TCR have the potential to be more diverse compared to the conventional ab TCR? If so, how?

Answer 23

The yd TCR has the potential to be more diverse by incorporating an extra D segment while rearranging its delta chain.

Question 24

What determines the tissue a specific yd T cell will migrate to?

Answer 24

The variable gamma and delta segments that get rearranged and incorporated on the TCR determine the location of the yd T cell in the body

Question 25

Describe the roles of yd T cells

Answer 25

Response to microbial infections (HMBPP)
Response to tumor cells
Early immunoprotection in young animals
Immunoregulation, dampening of inflammation

Question 26

Describe the role of the hypervariable region 4 (HV4) in the yd TCR

Answer 26

It mediates the segregation of yd T cells to specific tissues by sensing tissue-specific antigens.l

Question 27

Do yd T cells recognize antigens in the context of MHC presentation?

Answer 27

No, the long CD1 and CD2 regions prevent interactions with MHC molecules.

Question 28

How do yd T cells sense foreign phosphoantigens?

Answer 28

The foreign phopshoantigens are released into a presenting cell (i.e. monocyte) and lead to the conformational change of butrophilin on the cell surface. The yd TCR is able to bind this altered butrophilin an d initiate a response.

Question 29

What ligands are recognized by yd T cells on stressed/cancer cells?

Answer 29

Unconventional MHC molecules:

MICA and MICB in humans
T10/22 in mice.

Question 30

Are yd T cells cytotoxic? If so, do they share the same mechanisms of killing employed by alpha/beta CTL?

Answer 30

They are cytotoxic and share the same mechanisms (Perforin+granzyme combo, FasL).