immune cells and Organs Flashcards
What does Primary lymphoid organs do and what do secondary lymphoid organs do?
Give the secondary lymphoid organs
Primary (thymus, and bone marrow) : lymphocytes are produced- lymphopoiesis.
Secondary: lymphocytes interact with antigens and other lymphocytes
Organs:
-Spleen
-Lymph Nodes
-Mucosal Associated Lymphoid Tissue (MALT)
Describe what happens with the lymphocytes?
Both T and B precursor come from heamatopoeitic cells from bone marrow
- mature lymphocytes enter the circulation
- leave and go into secondary lymphoid tissue
- keep circulating until they meet antigen or die
What is the general structure of the thymus gland and explain the staining?
Bi-lobed in mammals, located in the thorax. Lobes are divided into lobules by septa- and in each there are cortex and medulla. Cortex contains immature thymocytes and some become mature in the medulla.
It has a capsule. You get darker staining at the peripheries.
You find whirls of fibroblasts called hassall’s corpuscles in humans that give rise to regulatory T lymphocytes( prevent autoimmune and maintain tolerance to self antigens)
Medulla - not very stained.
Cortex- Very stained
How does the thymus change during infection?
It doesn’t
How does the thymus change with age?
- atrophies with age
- Reduced output of new t cells, so less diverse (OLIGOCLONAL)
- areas of active T cell production are replaced with adipose tissue and thymus size decreases
- more memory cells
- number of T cells stays the same
- total size of the mature T cell pool does not decline substantially with age.
Where are white blood cells produced in foetus and adults?
Foetus: white cell also produced in liver and spleen
Adult: mainly the ends of the long bones (most marrow). The marrow becomes less cellular with more fat droplets.
What does the red marrow and yellow marrow produce?
Red: produces blood cells
Yellow: fat
what does the lymphatic system allow?
- allows all fluid to be drained through the lymph nodes
- it is filtered through the lymph nodes to identify pathogens before it goes into the blood
- allows you to find out whether there is an infections and WHERE it is
What are the names of lymphatic vessels that bring lymph to and from the lymph nodes?
Afferent – in; efferent - out
Lymph arrives at the lymph node through several AFFERENT vessels and leaves through one EFFERENT vessel at the hilus.
Describe the structure of the lymph node
Within the lymph node there are LOTS of lymphocytes.
- Are round or kidney shaped and have an indentation at the hilus where the blood vessels enter and leave the node.
- Cortex is a B cell area ( on the outside)
- Paracortex is a T cell area
- B lymphocytes aggregate into FOLLICLES
What happens during on going immune response
Proliferation of B lymphocytes- GERMINAL center forms which causes lymph nodes to swell
What are germinal centers and what do they indicate?
Germinal centers are accumulations of B cells – the germinal centers indicate the presence of on-going infection
How do lymphocytes enter and leave the lymph nodes?
- come in the circulation and leave via HIGH ENDOTHELIAL VENULES and enter the lymph.
- move from lymph node-lymphoid vessels- blood via thoracic duct
- directed by chemokines.
- if there is an infection, cells which recognise the infectious agent are held in the lymphoid tissue where they proliferate and differentiate
Where do lymphocytes exit the circulation and enter the lymph?
High endothelial venules
What is the immunological role of the spleen?
It filters the blood for antigens
Describe the organisation of lymphoid tissue around the arteries in the spleen.
White pulp: constitutes the major initiator of responses to blood-borne antigens (viruses).
Made up of Primary follicle, Marginal Zone and Periarterial lymphatic sheath.
Red pulp: general filter for blood.
Red pulp makes most the spleen than the white pulp.
Splenic artery- brings blood in and divides into central arteriole, and is surrounded by lymphoid tissue which contains lymphocytes. This is where the white pulp is.
Around the central arteriole=Pariarterial lymphatic sheath (PALS)
- nearest to arteriole is mainly T area
-Adjacent to PALS is B cell area which is the follicles.
-if there is ongoing immune response you can get germinal centers in the spleen.
what type of infections are those without a spleen most susceptible to?
Infections with encapsulated bacteria.
Encapsulated= encapsulated with polysachharide.
What is an example of Mucosa Associated Lymphoid Tissue ( aggregates of lymphoid tissue that do not have a tough outer capsule)
Peyer’s patches:
-regions of lymphoid tissue found in the wall of the gut
-Large aggregates of lymphocytes found just below the intestinal epithelium.
-organised into B and T cell areas
-Follicles and Germinal centers (during immune response) can be seen. Mainly B lymphocytes found.
-there are lots of intraepithelial lymphocytes(do not need priming. Upon encountering antigens, they immediately release cytokines and cause killing of infected target cells).
M cells (microfold) in the epithelial layer sample antigens from the gut and deliver antigens to the lymphocytes in the peyers patch.
Which immune cells are found in the subcutaneous immune system?
Langerhans cells
-Dendritic cells of skin and mucosa: capture antigens and migrate via lymphatic vessels to draining lymph nodes.
Keratinocytes: detect damage in the skin and secrete signalling molecules to communicate this.
-Tissue resident macrophages
-T Lymphocytes: migrate to the skin if necessary.
what type of cells are found in the skin
DENSE network of immune system cells:
Mainly:
Langerhans and intraepidermal lymphocytes.
What are the three receptor interactions involved in the extravasation of lymphocytes?
Selectin binding – weak interaction Chemokine receptor on the lymphocyte binds to chemokine on the HEV(high endothelial venules)
Integrins on the lymphocytes bind to ICAM-1.
Describe the sequence of events that occur when lymphocytes move out of the circulation.
The lymphocytes are initially rolling along the endothelial layer – selectins bind and slow down the rolling. Then the chemokine receptor on the lymphocyte will bind to the chemokine on the HEV (high endothelial venules). When the chemokine binds, the integrin will be changed to the high affinity state allowing it to bind with ICAM-1
which allows immobilisation of the lymphocytes and allows them to move from the circulation and enter the tissue
How do ALL lymphocytes look under a microscope?
-large nucleus and small cytoplasm.
What receptors do all T cells have?
CD3
What other types of receptor do T cells have?
90% of T cells have alpha-beta receptors and 10% have gamma-delta
Of the alpha-beta receptors:
2/3 have CD4 and 1/3 have CD8
What are the two main receptors that all B cells have?
CD19 and CD20
- Express MHC class II
- can present antigens to Helper T cells
What are the T cell subsets
CD4+ = T helper cells, regulatory T cells - these secret cytokines CD8+ = Cytotoxic T cells- lyse infected cells, secrete cytokines.
What are the APC , location and what does it present to?
APC: Dendritic cells Follicular dendritic cells B cells Activated Macrophages
Location: Widespread e.g. skin and mucosal tissue; migrate to draining lymph nodes lymphoid follicles lymphoid tissue lymphoid tissue, peripheral tissues
Presents to: T cells B cells T cells T cells
What is Cluster of
Differentiation (CD)
Developed using monoclonal antibodies, clusters of which recognised the same cell surface antigen.
CD is used as cell markers
How big is the human lymph node?
1-15 mm across
what type of antigen do T cell and B cell recognise?
What is the antigen receptor in T cells and B cells structure
What CD do T cells and B cells present?
Where are T cells and B cells produced
T cell: Recognize processed antigen presented at the cell surface by MHC molecules
B cell: Recognize intact, free antigen (not presented by MHC molecules)
T cells:Antigen receptor is either αβ or γδ TCR
B cells: Antigen receptor includes cell surface antibody
T cell: All T cell express CD3: T cells express CD4 or CD8, but not both
B cells: Express CD19 and CD20 at surface
T cell: Produced by Thymus
B cell:Produced by Bone Marrow
where are B cells made and differentiated?
B cell differentiation is centripetal with the stem cells under the bone and most mature phases of the B cell pathway found nearer the centre of the marrow.
