T killers and T helpers

Question 1

What are the subpopulations of T lymphocytes

Answer 1

T helpers
T killers
T regulatory

Question 2

Can any T cell recognise pathogen directly

Answer 2

No
They recognise foreign antigen on other cell eg APC with self MHC

Question 3

Which MHC class does T killers recognise

Answer 3

MHC1- for nucleated cells
T killers have co receptor CD8

Question 4

Which MHC class does T helpers recognise

Answer 4

MHC2- immune system cells like b and macroohages
T helpers have co receptoer CD4

Question 5

Where is MHC1 synthesises

Answer 5

ER

Question 6

What is the origin of antigenic peptides on class I
MHC?

Answer 6

• proteins degraded by proteosomes into peptides (8-10 amino acid chain )
• TAP (transporter for antigen processing) transfers these peptides to ER
• MHC1 finds these peptides and binds to them

Question 7

A cell presenting MHC1 and foreign peptide is not acc a APC.
What is it known as

Answer 7

target cell

Question 8

How are T killers like Natural killers of innate immunity

Answer 8

Forces target cell to undergo apoptosis

Question 9

How does T killers force cell to undergo apoptosis
2 mechanisms

Answer 9

1. They carry FAS ligand which bunds to FAS receptor (death receptor) on target cell
2. They release perforin( make pores) and granzymes (cuts capases)

Question 10

How do T killers recognise normal cell with MHC1 or a virus cell

Answer 10

Normal cell has fragments of normal proteins

Virus infected cells have unusual peptides on MHC1 and will react

Question 11

What happens if virus blocks apoptosis

Answer 11

More holes are made on the membrane by perforin and induces necrosis

Question 12

What do T helpers need to recognise

Answer 12

They recognise antigen with MHC2 ( not native antigen) on mononuclear phagocytes and b cells

Question 13

What is the difference between antigen presentation of MHC2 and MHC1

Answer 13

MHC1- antigenic peptides are endogenous

MHC2- antigenic peptides exogenous

Question 14

Antigen presentation of T helpers

Answer 14

originate from proteins that are not synthesized in the
antigen-presenting cell but taken from outside by phagocytosis and cut by lysosomal enzymes.

MHC2 are sent to the phagolysosome, bind the antigenic peptides and are
transported to the cell surface for antigen presentation.

Question 15

Can B cells act as phagocytes

Answer 15

They are not phagocytes

But they can have some qualities like endocytosis and intracellular digestion

So they can internalize the antigen bound to their Ig receptor and then present it.

Question 16

What is important in order to presetn exogenous antogens to T helpers

Answer 16

Self peptides cannot settle into the cleft of MHC2
So cleft is occupied by protein INVARIANT CHAIN
Then protease cuts it and makes CLIP

Question 17

What are the subpopulations of T helpers

Answer 17

Th1- cell mediated immunity
Th2-humoral immunity

Question 18

Th1 cells assist macrophages in phagocytosis. Why is this needed?

Answer 18

Sometimes bacteria and parasites get engulfed by phagocytes but they still survive and reproduce in them :(

Leishmania and toxoplasma does this

Even tho they havent killed pathogen yet, the macrophages will still present their antogens with MHC2.

TH1 ACTIVATES MACROPHAGE BY SECRETING INTERFERON GAMMA

Now macrophage can kill parasite in them :)

Question 19

Interferon gamma released by Th1 is a paracine signalling molecule.
What are they called

Answer 19

Cytokines

Question 20

What is thymus independent

Answer 20

Only a few antigens can induce antbodies without the help of Th2

NO CLASS SWITCH SO ONLY IGM

Most antigens are thymus-
dependent. B cells specific for them need the help of Th2 cells.

Question 21

Pathogen, TH2 and B cells

Answer 21

1. After binding antigen, the B cell engulfs it, digests it and presents it with MHC-II.
2. A Th2 cell specific for the same Ag “sees” it and activates the B cell by secreting cytokines.
3. Cytokines cause the B cell to mature to a plasma cell and secrete antibodies

Question 22

How do u obtain antibody against hapten

Answer 22

Hapten binds to a protein bc protein provides epitooes for th2

Question 23

How are t helper cells attacked by HIV

Answer 23

HIV binds to t helper CD4 receptor

No adaptive immunity

Causes AIDS

Question 24

What is TYPE IV hypersensitivty: why is it termed delayed?

Answer 24

Occurs only 24-72 hours after exposure

Delay due to time required for T cell
differentiation, cytokine +chemokine secretion,
and accumulation of leukocytes at site.

Question 25

what is type 4 hypersensitivity based on

Answer 25

Th1 cells
- T killers / activated macrophages

type IV involves
antigen-specific effector T cells. (while others mediated by antibodies)

Question 26

Examples of type 4 hypersensitivity

Answer 26

• Tuberculin reaction
• Contact dermatitis,
• Transplant rejection,