2 Immune Cells And Organs Flashcards
*Q: What is the process of lymphocyte production called?
A: LYMPHOPOIESIS
*Q: What are lymphoid organs? What are they the site of?
A: Tissue in which lymphocytes interact with non-lymphoid cells.
Sites of initiation and maturation of adaptive immune response
*Q: What are the primary lymphoid organs where T and B lymphocytes develop? What are the precursors for B and T cells?
A: Thymus - T cell maturation
Bone Marrow - B cell maturation
haematopoietic stem cells in the bone marrow
*Q: 3 secondary lymphoid organs.
A: Lymph nodes
Spleen (white pulp)
Mucosa-Associated Lymphoid Tissue (MALT)
Q: Are defects in primary and secondary lymphoid organs dangerous? What can treat them?
A: A defect in the primary lymphoid organs is very serious because you won’t produce your own lymphocytes. This can only be treated with stem cell transplant.
We can manage without some of our secondary lymphoid organs
Q: Anatomically, where is the thymus?
A: below the thyroid gland
Q: What does the microscopic analysis of a stained section of thymus show?
A: shows lobules within the lobes which are packed with lymphocytes
Medulla (middle) - NOT very stained
Cortex (periphery) - VERY stained
*Q: What is the thymus structure? Diagram.
A: bi lobed
lobules within the lobes which are packed with lymphocytes
There are septa dividing the lobe into lobules-> each lobule is histologically defined regions of cortex and medulla
cortex contains immature thymocytes-> some are selected to become mature thymocytes in medulla
It has a capsule
In human’s you get whirls of fibroblasts called HASSALL’S CORPUSCLES= where regulatory T lymphocytes develop
REFER
Q: What is the role of regulatory T lymphocytes?
A: important role in helping regulate our immune responses.
*Q: How does the thymus appearance change after stimulation by an antigen (infection)?
A: no obvious changes
Q: How does thymic output change with age? What happens? ->(7)
A: reduced output of new T cells
The total number stays the same
LESS DIVERSE repertoire of T cells
More memory cells
They become OLIGOCLONAL - less diverse
more fatty tissue in the thymus - size of the thymus DECREASES
Q: What happens to T cells in the thymus?
A: T-cells are ‘educated’ - learn how to recognise cells presenting the antigen in the thymus
*Q: How do lymphocytes and APCs recirculate?
A: Lymphocytes and antigen-presenting cells recirculate through lymphatic vessels: FROM tissues VIA lymph nodes and the spleen INTO the blood
Q: What does the lymphatic system allow? (2)
A: Allows all fluid to be drained through the lymph nodes where it is filtered to identify any pathogens before it goes back into the blood.
Allows you to find out whether there is an infection in the body and where the infection is.
*Q: What is the structure of a lymph node? Diagram.
A: Blood supply-
Afferent - IN = several vessels
Efferent - OUT = one (at hilus)
B cell areas tend to be on the outside- aggregate into FOLLICLES
REFER
round/kidney shape and have indentation at hilus where blood vessels enter and leave node
medulla surrounded by paracortex (T cell area) and cortex around that (B cell area)
*Q: How does the structure of a lymph node change upon infection? (3)
A: PROLIFERATION of B lymphocytes - GERMINAL CENTER forms
Germinal Center - lymphocytes are rapidly proliferating to produce antibodies against the pathogen which caused the infection.
This makes your lymph nodes swell
Q: How do lymphocytes enter the lymph nodes?
A: come in the circulation and leave via high endothelial venules and enter the lymph nodes.
They are directed by CHEMOKINE gradients via chemokinesis to their correct position.
Q: How is an immune response triggered in a lymph node?
A: Dendritic cells migrate through the lymph and into the lymph nodes where it presents antigens to recirculating lymphocytes to trigger an immune response
Q: What is the role of the spleen?
A: Filter for antigens IN THE BLOOD
*Q: What is the structure of the spleen? Diagram.
A: White pulp immediately surrounds the blood vessels in the spleen
WHITE PULP - where the lymphocytes are
RED PULP - the rest of the spleen is red because this is the site of turnover of red blood cells
Splenic Artery brings the blood in and is surrounded by lymphocytes.
The area absolutely adjacent to/around the central arteriole is the periarterial lymphatic sheath (PALS) - mainly a T cell area
Adjacent to PALS is the B cell area= follicles either primary or secondary and around those is marginal zone= seems to be primary site of entry of T and B lymphocytes into white pulp
REFER
*Q: How does the structure of the spleen change upon infection?
A: If there is an ongoing immune response you can get germinal centers in the spleen.
Q: What are people without spleens more susceptible to?
A: INFECTIONS WITH ENCAPSULATED BACTERIA- Encapsulated = encapsulated with polysaccharide
*Q: What is MALT? Where is it found? 3 examples.
A: mucosal associated lymphoid tissue = aggregates of lymphoid tissue which do not have a tough outer capsule
lamina propria and sub-mucosal areas of the gastrointenstinal, respiratory and genitp-urinary tracts
tonsils and appendix and peyers patches
Q: What structures are near likely sites of infection? (2)
A: some lymphoid tissue
MALT (mucosa-associated lymphoid tissue) and the cutaneous immune system are at these places
Q: What is an example of gut associated lymphoid tissue?
A: PEYER’S PATCH - large aggregates of lymphocytes
Q: How is the peyer’s patch organised? (5)
A: Organised into B and T cell areas
Follicles can be seen here
Villi contain draining lymph vessels
There are lots of intraepithelial lymphocytes
include M cells
Q: What do M cells do? What structure are they related to?
A: M Cells (microfold) - samples antigens from the gut and deliver antigens to the lymphocytes in the Peyer’s patch
to do with function of MALT
Q: How does the structure of the peyer’s patch change upon infection?
A: Contain germinal centers during immune responses
Predominantly B lymphocytes found here
Q: Which cells are present in the cutaneous immune system? (7)
A: LANGERHANS CELLS - dendritic cells of the skin and mucosa -> Capture antigens in their local environment // Migrate via lymphatic vessels to draining lymph nodes
Lymphocytes
Keratinocytes- detect damage in skin and secrete signalling molecules to communicate this knowledge of damage
Dermis - you get tissue-resident macrophages
T lymphocytes circulate and can migrate to the skin if necessary
There is a dense network of immune cells in the skin (mainly langerhans cells and intraepidermal lymphocytes)
*Q: Why is a mechanism for recirculation of lymphocytes required? (3)
A: Problem: There are large numbers of T cells and B cells with different specificities
There is a very small amount of antigen
There is need for a mechanism allowing the correct lymphocyte to come into contact with the antigen.
Q: Describe the mechanism that allows circulating lymphocytes to know when they have reached the high endothelial venules HEV. (5) Why is this important?
A: good as they need to know when it is time for them to leave the circulation and enter the tissue
- Rolling
- L selectin from the lymphocyte binds to CD34. Weak bond
There are special chemokines that are bound to the HEV - let lymphocyte know that they’ve reached the right place to enter the tissue.
- binding of lymphocyte to chemokine on HEV
surface receptor on the lymphocytes: Integrin: They have a low affinity and a high affinity binding form.
- binding of chemokine leads to activation of integrin in that it becomes its high affinity binding form (activation of the integrin to the high affinity binding form which leads to tight binding and immobilisation of the lymphocyte)
- Integrin can then bind to its ligand - ICAM-1 (Intracellular adhesion molecule 1) = adhesion
- The lymphocyte then becomes immobilised and can move into the tissue = transendothelial migration
*Q: Explain the use of CD (Cluster of Differentiation) markers for discrimination between lymphocytes.
A: All lymphocytes look the same under a microscope - large nucleus + small cytoplasm
Can be divided into B and T lymphocytes if we know where they’ve come from but they cannot be distinguished under the microscope.
EXPERIMENT: when people learnt to make monoclonal antibodies, they made monoclonal antibodies against the cell surface proteins of lymphocytes -> found that one particular cluster recognises one particular receptor and a different cluster recognises a different receptor.
It’s clusters of antibodies recognising cell surface proteins.
Q: Describe T cell receptors.
A: ALL EXPRESS CD3 - an integral part of the antigen specific receptor
There are two groups of TCR:
alpha beta - 90% in blood
gamma delta - 10% in blood
Out of alpha beta TCR:
CD4 - 2/3
CD8 - 1/3
Q: What are the 2 T cell subsets? Examples. What does each subset do?
A: CD4+ = T Helper Cells, Regulatory T Cells - these secrete cytokines
CD8+ = Cytotoxic T Cells - lyse infected cells, secrete cytokines
Q: What type of antigen do T cells recognise? How?
A: Only recognise PROCESSED ANTIGENS
Recognised by the TCR
Antigens must be presented by an Antigen-Presenting Cell on their cell surface by an Major Histocompatibility Complex (MHC) molecule
Q: Describe B cell markers. What do they express? What can they present antigens to?
A: They don’t have any T cell markers
All Express CD19 and CD20
Express MHC Class II
Can present antigens to Helper T Cells
Q: What type of antigen do B cells recognise?
A: Recognise INTACT ANTIGENS- DO NOT have to be processed and presented.
Q: What is the BCR? Specificity?
A: membrane anchored form of the antibody that they produce when activated.
The BCR has the same specificity as the antibody they produce when activated
Q: What do APC do? How?
A: present processed antigens to T lymphocytes
The cells capture antigens from the outside - process the antigens - present peptides on the cell surface via MHC - triggers an immune response
*Q: What are the 3 types of APC? Location? What is a 4th type? What makes it different? What do they present to: B or T?
A: Dendritic Cells- widely spread eg skin and mucosal tissue - presented at sites of likely infection-> T
B cells- lymphoid tissue-> T
Activated macrophages (activated)- lymphoid tissue->T
Follicular dendritic cells- present to B cells- found in follicles in lymph nodes which trap antigens to help B cell responses in germinal centers
*Q: Difference between primary and secondary lymphoid organs in terms of role? (1,2)
A: primary generate lymphocytes from immature progenitor cells
secondary maintain mature naive lymphocytes and initiate an adaptive immune response
*Q: What happens during passage of lymph through node?
A: removal of particular antigens by phagocytic cells -> transported to lymphoid regions of node
*Q: What are Peyers patches? Found? Structure?
A: regions of lymphoid tissue found in gut wall
REFER
Q: What are High Endothelial Venules (HEV)?
A: a specialised endothelium with a number of molecules involved in arresting the lymphocyte
HEVs enable lymphocytes circulating in the blood to directly enter a lymph node (by crossing through the HEV)
Q: What’s the site of haematopoiesis? How does production change with infection?
A: bone marrow
Increased white cell production during infection
Q: Where are blood cells made in foetus vs adult? Describe adult.
A: Foetus - these cells are also produced in the liver and spleen
Adults - mainly the ends of the long bones where you find most of the marrow - the marrow becomes less cellular with more fat droplets
