Primary Lymphoid Organs

What is the site of T and B lymphocyte development and education?

Primary lymphoid tissues

What is central tolerane?

T and B cells are tolerant of self antigens

Where are T cells developed?

Thymus

Where are B cells developed?

Bone marrow

What extra lymphoid tissue do ruminants and horses have?

The intestine (both primary and secondary)

What are the primary lymphoid tissues?

Thymus

Bone marrow

Intestine (horse and ruminant)

What are the secondary lymphoid tissues?

Tonsils

Spleen

Bone marrow

Lymph nodes

Urogenital system

Mammary glands

Respiratory tract

Intestine (horse ruminant only)

What is the development of fetal stem cells look like?

Fetal yolk sac TO Fetal liver TO bone marrow

What happens at primary lymphoid tissue?

Lymphocyte development and education

What happens at secondary lymphoid tissue?

Foreign antigen interaction and proliferation

What is the primary lymphoid tissue in brids?

The bursa

What are ileal peyers patches?

They are primary lymphoid organs in ruminants and horses

T/F some ells will leave the bone marrow and go to the thymus to become a T cell?

True

What are the steps to BCR development?

VDJ rearrangement followed by negative selection

How do B cells leave the bone marrow?

Mature, but naive

What is gene rearrangement?

Random selection of gene segments resulting in genetic diversity of BCR. Occur is primary lymphoid organs

What is somatic hypermutation?

High frequency mutations in variable regions of Ig genes after B cell activation. Occurs in germinal centers of lymph nodes

When does somatic hypermutation occur?

After the B cell found its antigen

Do adult birds have a bursa?

Sometimes, but it is usually shrunk fully

What happens in the cortex of the bursa?

B cell proliferation

What happens in the medulla of the bursa?

Negative selection of B cells

About how much of the circulating lymphocytes is B cells?

20%

What are the only cells that produce antibodies?

B cells

Where does the thymus grow from?

Third pharyngeal pouch

What are thymocytes?

T-cells that just arrived in the thymus from the bone marrow

What are the steps to becoming a T lymphocyte after getting to the thymus?

Develop a TCR

Become class restricted
Tolerized to slef

Describe the structure of a TCR

A heterodimer of 2 chains. Either a gamma and delta or alpha and beta

What species has more gamma and delta TCRs?

Ruminants

What is important of gamma delta T cells?

They are broader recognition more at mucousal sites

What part of a T cell is required for signal tranduction?

CD3

What are the parts of a beta or delta chain?

Variable V, D J segments with a constant C gene segment

What are the parts of a alpha or gamma chain?

Variable V, J and constant C genes. NO D SECTION

How are TCRs created?

Somatic recombination

What does recombinase do?

It loops genes out

What is SCID?

Severe combined immunodeficiency, cannot develop B or T cells

What are the steps of T cell development?

Proliferate and rearrange TCR genes

CD3, CD4, and CD8 are all expressed

What is different in the development of gamma delta TCRs compared to alpha beta?

Gamma delta leave the cell after TCR is expressed

What is said to happen to T cells in the thymus?

They are educates

How do T cells become class restricted?

They recognize antigens presented on thymic epithelial cells on either MHC 1 or MHC 2 molecules

T/F Cells with TCR that can bind MHC plus Ag are positively selected in the thymus?

True

What happens if the TCR binds to MHC I?

The cell will upregulate CD8 expression and down regulate CD4 expression

What happens if the TCR binds to MHC II?

The cell will upregulate CD4 expression and down regulate CD8 expression

What species has a lot of CD4 and CD8 T cells in circulation?

Pigs

What happens first positive or negative selection for T cells?

Positive

What happens to cells that bind self MHC plus self Ag?

They are negatively selected

How does negative selection work?

AIRE genes encode self peptides to see if the TCR will bind to it

T/F you are looking for a goldilocks middle ground when undergoing T cell negative selection?

True you dont want to bind to self things too hard or too lightly

What cells have AIRE genes?

Thymic medullary epithelial cells

What happens to the thymus later in life?

It shrinks so that it has a little function but not much

What happens to IgM, IgG, and IgA if there was never a thymus?

normal IgM but low IgG and IgA