immune cells and organs Flashcards
Where are lymphocytes produced?
Primary lymphoid organs.
They are produced by a process called lymphopoiesis.
What are secondary lymphoid organs?
Where lymphocytes can interact with antigens and other lymphocytes.
- spleen
- lymph nodes
- mucosal associated lymphoid tissue (MALT)
Description of primary lymphoid organs?
Bone (marrow) and thymus
The precursors of both B and T cells come from haematopoetic stem cells in the bone marrow.
Describe secondary lymphoid tissue
Mature lymphocytes enter the circulation and recirculate until they meet their antigen or they die.
How is a defect in the primary lymphoid treated?
Stem cell transplant- it is very serious because you cannot produce your own lymphocytes.
Can we manage without some of our secondary lymphoid tissues?
YES!
This is why we can get rid of our spleen
Describe the thymus
Located below the thyroid gland and is bilobed.
It is packed with proliferating lymphocytes.
Describe this microscope picture
- there are lobules within the lobes which are packed with lymphocytes
- Medulla (middle) not very stained)
- Cortex (periphery)- very stained
What does a thymic lobe look like?
Medulla in the middle, cortex on the outside
Septa divide the lobes and the lobules
There are whirls of fibroblasts called HASSALL’S CORPUSCLES where T regulator cells are developed.
What happens to our thymic output when we get older?
T cell production declines with age.
- When you are young, you have a high output of new T cells with new specifities
- When you age, there is a reduced output as there is more fatty tissue in the thymus and the size of the thymus decreases
THE NUMBER OF T CELLS IN OLDER PEOPLE IS THE SAME AS YOUNG PEOPLE, but there is less diversity in TCRs. They have more memory cells. The T cells of old people become oligoclonal (less diverse). If an old person is exposed to new infection, they are less likely to produce an efficient t cell response.
Where does haemotopoesis occur?
Bone marrow.
There is an increased white cell production during infection.
IN BABIES- these progenitor cells are also produced in the liver and spleen
IN ADULTS- mainly the ends of the long bones where most of the marrow lives- the marrow becomes less cellular with more fat droplets.
What is the difference between red and yellow marrow?
Red = produces blood cells
Yellow= fat
What is the lymphatic system?
Fluid drained between the tissue cells are absorbed through the lymph nodes.
It is taken to the lymph nodes to scan for pathogens before it goes back into the blood.
This allows for the identification of any infection in the body and where it is.
Describe the lymph node
afferent lymphatic vessel = in
efferent= out
there are lots of lymphocytes in the lymph node- highly organised- b and t cell areas ( B cells are on the outside)
Where do B lymphocytes go from the lymph node?
The B lymphocytes aggregate to follicles (on the outside)
In an immune response, what happens when the B cells proliferate?
A germinal centre forms.
Lymphocytes proliferate to produce antibodies against the pathogen. The lymph nodes swell. So if you have germinal centres, you know that there is an ongoing infection.
What is the point of the spleen?
Filters for antigens in the blood.
Lymphocytes are in the white pulp. The white pulp sits around blood vessles.
People who don’t have a spleen are highly susceptible to infection with encapsulated bacteria.
The lymphocyte area in the spleen
the splenic artery is adjacent is the periarterial lymphatic sheath (PALS)- this is mainly a t cell area.
Adjacent to PALS is the b cell area.
What is the gut associated lymphoid tissue? (GALT)
It is a form of the MALT- tries to protect the body from invasion in the gut.
There are organised B and T cell areas. There are also follices and germinal centres.
PEYER’S PATCH- large collection of lymphocytes.
The villi contain draining lymph vessels and there are lots of intraepithelial lymphocytes.
Describe peyer’s patch
- predominantly B lymphocytes
- contain germinal centresduring immune responses
What is the cutaneous immune system?
defence for the skin:
- langerhans cells- dendritic cells of the skin and mucosa- capture and take antigens to lymph node
- Lymphocytes
- Keratinocytes good at detecting damage- secrete signalling molecules
- Dermis- tissue resident macrophage
- T lymphocytes circulate and can migrate to the skin if necessary
cutaneous immune system by fluorescent imaging
How does T lymphocyte enter the lymph node to become activated?
- HEV (high endothelial venules) arrests the lymphocyte, immobilising it and making it easier to move to the correct place.
- chemokines are bound to HEV and pollet the lymphocyte to let them know that they’ve reached the right place.
- The lymphocytes ROLL along the surface of HEV, binding to several molecules as they roll along.
- Integrin can be found on the surface of the lymphocytes. Integrin has a high and low affinity binding form. When the chemokine receptor on the lymphocyte binds to chemokine on HEV, the integrin becomes high affinity.
- Integrin can bind to ICAM1 (adhesion molecule).
- The initial receptor on the lymphocyte is seletin WEAK AFFINITY
- The activation of integrin leads to tight binding and immobilisation.
just remember: ROLL, ACTIVATE, ADHERE
How many T lymphocytes do we have?
How does clonal selection occur?
there is a diverse repertoire of lymphocytes
Secondary lymphoid tissue- antigens are presented by APCs. The relevant lymphocyte with the complimentary receptor will proliferate.
Some cells will become memory cells.
