1.2 Lymphocyte Development

Question 1

What are the two types of T cell into which t lymphocytes can differentiate?

Answer 1

CD8 (killer)
CD4 (helper)

Question 2

Where do all blood cells develop? Which is the exception?

Answer 2

Bone marrow

T cells in the thymus

Question 3

Where do lymphocytes develop, and from what type of stem cell? Where does maturation occur for B and T cells?

Answer 3

Develop from bone marrow pluripotent haematopoietic stem cells

Mature in bone marrow (B cells) or thymus (T cells)

Question 4

What does the maturational pathway that leads to the development of immunocompetent lymphocytes involve?

Answer 4

Gene rearrangement
Lineage commitment
Education
Functional maturation

Question 5

Where do the instructions/signals necessary for a stem cell to become a lymphocyte come from?

Answer 5

Bone marrow microenvironment

Question 6

What do B cells recognise? Why does this differ from T cells?

Answer 6

B cells recognise native proteins

T cells recognise degraded proteins bound by major histocompatibility complex (MHC) molecules

Question 7

What are the two regions of the receptors?

Answer 7

Variable
Constant

Question 8

What is the light chain made up of?

Answer 8

Variable domain
Joining domain
Constant domain

Question 9

What is the heavy chain made up of?

Answer 9

Variable domain
Constant domain
Joining domain
Diversity domain

Question 10

How does diversity occur in T cell receptors?

Answer 10

Multiple variable and joining domains

Completely random order (1 V joins with 1 C and 1 J)

Question 11

What do all B cells start off expressing?

Answer 11

IgD
IgM

Question 12

What do Nude mice not have? What does this lead to?

Answer 12

No thymus
Therefore v. immunocompromised
Don’t make T cells

Question 13

What class of MHC do CD8 bind?

Answer 13

MHC CLass I

Question 14

What class of MHC do CD4 bind?

Answer 14

MHC Class II

Question 15

Why is the thymus critical for development of mature and competent T cells?

Answer 15

Absence of thymus means there is a lack of peripheral T cells
Leads to host being immunocompromised

Question 16

What type of lymphoid organ is the thymus?

Answer 16

Secondary
Where immune activation occurs

Question 17

What happens if a T cell develops with low interaction affinity?

Answer 17

Cells die by neglect
Don’t bind to MHC and therefore will be useless to host when infected

Question 18

What hapens if a T cell develops with high interaction affinity?

Answer 18

NEGATIVE SELECTION
Cells die by apoptosis
Bind strongly to self protein, if allowed to exit into periphery as likely to cause harm

Question 19

What happens if a T cell develops an appropriate interaction affinity?

Answer 19

POSITIVE SELECTION
Cells will be ‘rescued’
Binding is not too weak or too strong
Cells are encouraged to survive and exit into the periphery where they form a major part of defence system

Question 20

What is central tolerance? How does it occur?

Answer 20

Mechanism by which newly developing T cells and B cells are rendered non-reactive to self

Thymocytes which are strongly reactive to self/self-MHC are deleted