Week 6: The lymphoreticular system Flashcards
What is the MPS and what cells are in it?
Mononuclear phagocytic system.
monocytes, macrophages, and dendritic cells
From what cells are the lymphoreticular system derived from?
White blood cells
What are the two groups from which the lymphoreticular system derive from?
Lymphoid cells (B and T lymphocytes)
Phagocytes (neutrophils, eosinophils) and the MPS
The haematopoietic cell differentiates into which two cells?
common myeloid and lymphoid
What cells do myeloblasts form?
Derived from the common myeloid progenitor they form:
-monocytes
-eosibophils
-basophils
-neutrophils
Where does haematopoiesis occur?
In the medulla of the bone marrow
What other progenitor cell is found in the bone marrow?
Megakaryocytes - progenitor cells for platelets
Where do immature T cells originate from and where do they travel?
Bone marrow -> thymus
Into what cells do T cells differentiate to?
T helper cells- help B cells and APCs
T killer (cytotoxic) - kill viruses etc.
T regulatory - suppress the immune response
How are T helper and T killer cells characterised?
T helper- surface protein CD4
T killer- surface protein CD8
Where do B lymphocytes mature?
In the bone marrow
What cells do B cells differentiate into?
Plasma cells or B memory cells
What is the function of a monocyte?
To ingest microorganisms, cell debris (phagocytic cells)
Where and what do monocytes differentiate into?
In the tissue to macrophages
Name the 4 types of macrophages in the body
Osteoclasts - bone resorption and remodelling
Kupffer cell - found in the liver
Microglia- found in the brain
Langerhan cell - APC in the skin
What is the function of a dendritic cell?
To process antigenic material and present it to the cell surface to a T cell
Where are the dendritic cells found?
Found in tissues in contact with the external environment such as the skin (Langerhans’s cells)
What are the two common immune responses
Innate immune response and the adaptive immune response
What occurs in the innate immune response
-MPS and granulocytes are activated
-Protein components (e.g. interleukins)
-Inflammation
-Cells support the adaptive system
Where is the thymus located?
It is a flattened lymphoid organ located in the base of the neck
What are the functions of the thymus?
-Development of T cells from bone marrow
-Apoptosis of T cells
-Secretion of hormones to regulate t cells
How is the thymus organised?
Into lobules with an outer cortex and an inner medulla
What is the difference between the adult and infant thymus?
In the mature thymus the lymphoid tissue is separated by adipose tissue
Where do immature T cells enter in the thymus?
In the cortico-medullary junction
What happens in the outer cortex of the thymus?
Large lymphoblasts divide to produce clones of smaller mature T cells
What type of selection of T cells occurs first?
Positive selection- only the T cells which recognise the MHC molecules continue to divide and mature
What selection occurs last and where?
In the medulla of the thymus, negative selection - any T cell with recognising self-antigens on the APC will be deleted (only those who don’t recognise a self antigen live)
As T cells mature where do they migrate towards?
From the cortex to the medulla
What 2 cells are found in the medulla of the thymus?
Hassall corpuscles and thymic interdigitating cells
What are Hassall corpuscles?
A group of keratinised cells (thought to be degeneratifve)
What are thymic interdigitating cells>
Dendritic cells that play a role in clonal deletion ( negative selection)
What are the functions of lymph nodes?
-Filtration of lymphatic fluid for antigens
-Antigen processing
-Bring together antigen and APCs to facilitate immune response
-Activation of B and T lymphocytes
-B cells mature into plasma cells
How does the structure of lymph nodes allow it to perform its function?
-Sieve for lymphatic fluid (cortical inuses)
-Many APCs for antigen presentation
-Highly vascular
Describe the structure of the lymph nodes
Organised in a reticular network enclosed by a capsule (fibrous tissue), within the cortex there are follicles (primary follicles contain purely resting B cells)
Secondary B cells - are active
Why do secondary B cells look paler on H&E stain>
Because they are actively transcribing DNA so the DNA is less tightly wound. Therefore they look paler
Where are T cells activated>
In the paracortical area (deep into the cortex)
Where does the afferent sinus lymph drain into?
The sub-capsular sinus
Where are immature B cells contained?
Paler Germinal centre surrounded by a darker mantle zone (resting B cells) above that is the Marginal zone (paler)
Where do naive/immature B cells enter the LN?
Via high endothelial venules from the blood supply
Once in the LN what do immature B cells do?
Encounter an APC and macrophage and interact with the antigen. Undergo blast transformation
Outline the steps of blast transformation
- In the dark zone of the GC (form the central blast)
- Move into the light zone of the GC and differentiate into centrocytes
- Centrocytes differentiate into either memory or plasma cells
Where are centroblasts vs centrocytes found?
CB- In the darker zone closer to the medulla of the follicle
CC- paler zone of the GC towards the capsule
What are FDC
Follicular dendritic cells, they are the main APCs in LN follicles
What occurs in the paracortex?
T cell activation, they transform into larger immunoblasts (which divide into clones of T cells)
What are the main APCs in the paracortex>
Interdigitating dendritic cells
In the lymph node medulla how are branching medullary cords separated?
By irregular medullary sinuses
Where do B cells complete their maturation?
In the medullary cords
What is MALT?
Mucosa-associated lymphoid tissue ( lymphoid tissue distributed throughout the body at mucosal surfaces)
What makes up MALT?
GI tract (tonsils)
Lamina propria of the gut and respiratory tract
Peyers patches of the SI
How are the tonsils structured?
Organised in masses of lymphoid tissue forming the Waldeyer’s ring
How is tonsil tissue different and similar to lymphatic tissue?
-Contains lymphoid follicals and GC
-There are tonsillar crypts
What are Peyer’s patches?
Aggregated lymphoid follicles in the SI
Where is the spleen located?
Left upper abdomen
What kind of tissue makes the splenic tissue?
Red pulp and white pulp
What are the functions of the spleen?
Production of immune response
Removal of old cells (RBCS)
Recycling iron to the bone marrow
Haematopoiesis
How does the structure of the spleen allow it to perform its function?
Highly vascular rep pulp to filter antigens from blood
White pulp (B and T cells)
Contains many macrophages `
What is the spleen encapsulated by?
A capsule
What are trabeculae?
They form a path of branches of the splenic artery, from which smaller central arteries branch off to enter the splenic tissue
What are the differences between red and white pulp?
RP- highly vascular (bulk of tissue)
WP- lymphoid aggregates
- Consists of B cells and mainly T cells which surround the central arteries
What is PALS
periarteriolar lymphoid sheath
- are a portion of the white pulp of the spleen. They are populated largely by T cells and surround central arteries within the spleen;
Where are B cells in the white pulp
In follicles at the edges of PALS/central arteries
What are sheathed capillaries surrounded by?
Macrophages
What is RP made of?
Macrophages and BC - removes old RBCs
The sinuses in the RP are lined by what?
Endothelial cells (large SA where blood is in contact with the splenic tissue)
What marker characterises B cells?
C20
What marker characterises T cells?
CD4
What marker characterises cytotoxin cells?
CD8
