T Cells and B Cells. Flashcards
Where do all T cells mature?
In the thymus (T stands for thymus).
What happens to T cells once they arrive in the thymus?
They divide very rapidly and undergo somatic rearrangement.
Will T cells all express the same TCR?
No, the amount of diversity between the different TCRs that a T cell can express is huge.
What are the only somatic cells where somatic gene rearrangement takes place?
B and T cells.
What must happen to B and T cells before they can function?
They must be educated.
What are naive T cells also known as?
As thymocytes.
What is the name of the first step of T cell education?
Positive selection.
What occurs during the positive selection of T cells?
T cells bind to a self MHC and learn to recognise it.
This means that the T cell can recognise the MHC complexes of the body.
During positive selection what happens to the T cells that do not bind to a self MHC?
They are killed.
What is the 2nd step of T cell education?
Negative selection.
What occurs during the negative selection of T cells?
The T cell tries to bind to a self antigen.
During negative selection, what happens to T cells that form strong bonds with self antigens?
They will be killed.
What bonds do we want naive T cells to form self antigens?
Very weak bonds that are not strong enough to form an immune response.
What happens if the negative selection step of T cell education fails?
We can get an autoreactive T cell.
How long does T cell education in the thymus take?
Around 4-5 days.
What will be expressed by T cells that survive T cell education in the thymus?
CD-4 or CD-8 molecules.
What CD molecule is expressed by all T cells?
CD-3.
What are the CD molecules that can be expressed by the 2 types of T cells as they leave the thymus?
CD-3+ and CD-4+.
CD-3+ and CD-8+.
What happens to T cells once they have acquired the CD molecules?
They can migrate to the secondary lymphoid tissues.
Do naive T cells leave the thymus?
Yes.
Naive T cells enter the secondary lymphoid tissues.
Where do B cells mature in birds?
In the bursa.
Where do B cells mature in mammals?
In the bone marrow and in the Peyers patches.
What are Peyers patches?
The mammalian equivalent of a bursa.
Where in the body are peyers patches found?
All over the body.
What happens as the B cells mature in the bone marrow?
They undergo gene rearrangement so they can display a BCR.
What is the first step of B cell education?
Negative selection.
What occurs during the negative selection of B cells?
They are taught not to attack self antigens.
Any self reactive B cells undergo apoptosis.
Do B cells undergo positive selection?
No.
What happens to B cells once they have matured in the bone marrow?
They travel to secondary lymphoid tissues such as Peyers patches.
Can Peyers patches be thought of as primary and secondary lymph tissue?
Yes, but they mainly function as secondary lymph tissue.
What CD molecule is always expressed by B cells?
CD-79.
What CD molecules are expressed by T cells?
CD-3+.
CD-4+.
CD-8+.
What CD molecules are expressed by helper T cells?
CD-3+.
CD-4+.
What CD molecules are expressed by cytotoxic T cells?
CD-3+.
CD-8+.
What 3 cell types make up lymphocytes.
Natural killer cells.
B cells.
T cells.
What are the only lymphocytes to function in the innate immune system?
Natural killer cells.
What lymphocytes do not mature in the lymph tissue?
Natural killer cells.
What lymphocytes do not have receptors for antigens?
Natural killer cells.
