1.2 Lymphocyte Development Flashcards
What are the two types of T cell into which t lymphocytes can differentiate?
CD8 (killer)
CD4 (helper)
Where do all blood cells develop? Which is the exception?
Bone marrow
T cells in the thymus
Where do lymphocytes develop, and from what type of stem cell? Where does maturation occur for B and T cells?
Develop from bone marrow pluripotent haematopoietic stem cells
Mature in bone marrow (B cells) or thymus (T cells)
What does the maturational pathway that leads to the development of immunocompetent lymphocytes involve?
Gene rearrangement
Lineage commitment
Education
Functional maturation
Where do the instructions/signals necessary for a stem cell to become a lymphocyte come from?
Bone marrow microenvironment
What do B cells recognise? Why does this differ from T cells?
B cells recognise native proteins
T cells recognise degraded proteins bound by major histocompatibility complex (MHC) molecules
What are the two regions of the receptors?
Variable
Constant
What is the light chain made up of?
Variable domain
Joining domain
Constant domain
What is the heavy chain made up of?
Variable domain
Constant domain
Joining domain
Diversity domain
How does diversity occur in T cell receptors?
Multiple variable and joining domains
Completely random order (1 V joins with 1 C and 1 J)
What do all B cells start off expressing?
IgD
IgM
What do Nude mice not have? What does this lead to?
No thymus
Therefore v. immunocompromised
Don’t make T cells
What class of MHC do CD8 bind?
MHC CLass I
What class of MHC do CD4 bind?
MHC Class II
Why is the thymus critical for development of mature and competent T cells?
Absence of thymus means there is a lack of peripheral T cells
Leads to host being immunocompromised
What type of lymphoid organ is the thymus?
Secondary
Where immune activation occurs
What happens if a T cell develops with low interaction affinity?
Cells die by neglect
Don’t bind to MHC and therefore will be useless to host when infected
What hapens if a T cell develops with high interaction affinity?
NEGATIVE SELECTION
Cells die by apoptosis
Bind strongly to self protein, if allowed to exit into periphery as likely to cause harm
What happens if a T cell develops an appropriate interaction affinity?
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
What is central tolerance? How does it occur?
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
