4. CELLULAR IMMUNITY, T LYMPHOCYTES AND THE MHC STRUCTURE OF CELLS

Question 1

what are T-lymphocytes

Answer 1

Produced and matured in the thymus, but it is possible for the maturation to take place elsewhere. The lymphocytes have a dark nucleus. The T-lymphocytes are separated into Tc-cells, Th-cells and Treg-cells.

Question 2

Tc- cells:

Answer 2

acting in cellular immunity by killing the virus and bacteria infected cells.

Question 3

Th-cells

Answer 3

helps stimulate the activation of the Tc-cells and the B-lymphocytes needed for the immune response. will cause selective death amongst the Th-cells

Question 4

Treg-cells

Answer 4

helps regulate the activation of the Tc-cells and the B-lymphocytes needed for the
immune response.

Question 5

T- cells develop in 2 phases what are the 2

Answer 5

Antigen independant phase
Antigen dependant phase

Question 6

Antigen independent phase

Answer 6

preparations for when a vast number of pre-T-lymphocytes mature and become “virgin T-lymphocytes”.
On the surface of the virgin T-lymphocytes, there will be an Ig-like molecule appearing against a certain possible antigen structure. As this cell (Ti, initiator cell), gets into the circulation, the second phase begins.

Question 7

Antigen dependent phase

Answer 7

If the Ti-cell carries a CD4 cell surface antigen as well as the IgG-like molecule, it can recognise an antigen on the surface of an AP (antigen presenting) cell that has MHC-II also

Question 8

where do t-lymphocytes mature and origin

Answer 8

thymus
Origin: Bone marrow & liver

Question 9

Maturation in the thymus mains step

Answer 9

1) TCR
2) Immature
3) Positive selection
4) Negative selection:

Question 10

Maturation in the thymus step 1

Answer 10

1) TCR – T-cell receptors appear.

Question 11

Maturation in the thymus step 2

Answer 11

2) Immature T-lymphocyte surface receptors can bind most MHC structures and antigens.

Question 12

Maturation in the thymus step 3

Answer 12

3) Positive selection: T-lymphocytes that can bind self-MHC molecules will die survive, the rest will die.

Question 13

Maturation in the thymus step 4

Answer 13

4) Negative selection: T-lymphocytes that can bind self matters expressed together with self- MHC molecules will be killed or inactivated.

Question 14

MHC system

Answer 14

The natural ability to distinguish self from non-self.

Question 15

MHC sytem function:

Answer 15

Function: The “identity card” of the cells

Question 16

MHC-I

Answer 16

Composed of extracellular component encoded by an MHC-gene, plus some transmembrane and intracellular components.

Question 17

MHC-II

Answer 17

Composed of cell surface antigens similar to the
immunoglobulins. Found on antigen-presenting cells
(APC).

Question 18

MHC-III

Answer 18

Cell surface signals encoded by the MHC gene group.
- They do not play a role in the immune response directly

Question 19

MHC-I function

Answer 19

Different antigens of the MHC-I group are recognized by cytotoxic T-lymphocytes, if the cell binds some non-self antigen beside the MHC-I too.

Question 20

MHC-II function

Answer 20

APC send parts of the non-self antigen together with the
MHC-II structure onto the cell surface. The signal to the helper T-cell is the presence of the MHC-II structure together with the non-self antigen.