13 MHC and transplantation

Question 1

How many MHC molecules are there on the average mammalian cell?

Answer 1

50-100,000

Question 2

Where on the chromosome is the HLA complex?

Answer 2

6p21.3

Question 3

The HLA complex has three regions, which antigens does each encode?

Answer 3

1: HLA-A/ B/ C
2: HLA-DR/ DQ/ DP
3: HSP70, TNF, C4A, C4B, C2, BF, CYP21

Question 4

The two classes of antigens are found on different cells, which is where?

Answer 4

1: all nucleated cells
2: B lymphocytes (may be induced on T lymphocytes)

Question 5

The two classes of antigens have different structures - distinguish between them.

Answer 5

1: 45kd heavy chain and B2 microblobulin
2: 31kd a chain and 26kd B chain

Question 6

How is the HLA complex inherited?

Answer 6

En-bloc from each parental chromosome. Codominant expression - all inherited antigens are displayed (HLA phenotype).

Question 7

What is the difference between direct and indirect MHC recognition?

Answer 7

Direct: white blood cells from donor present directly to recipient T cells.
Indirect: foreign proteins are broken down and presented to T cells by MHCII of self APC’s

Question 8

What is sensitisation? Name three examples.

Answer 8

Any event which elicits an HLA directed immune response.

Pregnancy, blood transfusion, transplantation.

Question 9

How are the chances of an organ transplant determined by immunologically?

Answer 9

Blood group.
HLA type.
Sensitisation.

Question 10

What is hyper-acute rejection of an organ transplant?

Answer 10

Activation of the clotting cascade and complement system leading to loss of vascular integrity and DIC. Results in death.