11 Lymphoid tissues Flashcards
Where are lymphocytes produced?
Primary lymphoid organs
What is lymphopoieses?
Production of lymphocytes
Name 3 primary lymphoid organs
- Thymus
- Bone marrow
- Foetal liver
Name 3 lymphocytes
- B cells
- T cells
- NK cells
The adaptive immune response is comprised of
B cells and T cells
Two characteristics of the adaptive immune response
- Specificity: vast range of unique T cell and B cell receptors
- Memory: rapid expansion in response to secondary encounter
What is the primary site of haematopoiesis?
Bone marrow (non foetal)
Where is the B cell ‘repertoire’ generated?
Bone marrow
Where does final maturation occur?
Periphery (e.g. spleen)
Define repertoire
The range of genetically distinct BCRs or TCRs present in a given host (larger repertoire = more threats recognised)
What is positive selection of T cells?
- Can the T cell receptor signal
- Can the T cell receptor receive signals
What is negative selection of T cells?
-Does the cell react against our own body
Immature T cells enter the thymus from the bone marrow as
double negative T cells
Process of selection
- Enter as double negative
- Positive selection (double positive)
- Negative selection (single positive) or apoptosis
As age increases, thymus function?
Decreases
- Gets smaller, T cell production decreases
Where do lymphocytes interact with antigens and other lymphocytes?
Secondary lymphoid organs
Name 5 secondary lymphoid organs
- Spleen
- Mucosal associated
- Appendix
- Lymph nodes
- Lymphoid tissue
Where are lymphoid tissues found?
- Distributed around the body
- Interconnected via lymphatic system + blood
Examples of discrete organs?
- Lymph nodes
- Adenoids
Examples of distinct regions?
- Within a tissue
- Spleen
Afferent lymphatic vessels
Flowing into the lymph nodes
Efferent lymphatic vesseks
Flowing out of the lymph nodes
Key signals in lymphoid tissue
- Fibroreticular cells (CCL19, CCL21, IL-7)
- Follicular dendritic cells (CXCL13, BAFF, immune complexes)
B cells are compartmentalised in
B cell follicles
What is the first line of defence against infection?
Epithelial barriers
- Physical barrier
- Extensive lymphatic network
What are Peyer’s patches?
- Specialised secondary lymphoid tisses
- Found below the epithelium of the ileum of the small intestine
What is thymic involution?
Shrinking of thymus with age (associated with change in structure and reduced mass)
What is a germinal centre?
An anatomically restricted site where B cells undergo mutation and selection to generate high affinity antibodies
What is Waldeyer’s ring?
Ring of lymphoid tissues surrounding oral and nasal cavity (pharynx)
2 to 3 litres of lymph returned to blood each day (via superior vena cava)
The lymph is a rapid flow fluid draining lots of tissue of antigens
The lymph nodes
- Site to which lymphatic fluid is drained
- Source of antigens
Each naïve T cell recirculates once every
24 hours
Why do T cells have to return to the secondary lymphoid tissues
To receive its survival signal, otherwise if the cell was stuck somewhere, it would die
What happens when a blood vessel is running parallel to lymphatic vessels or high endothelial venules?
T cells migrate across blood vessels to high endothelial venules and then into the lymph node
What happens if a T cell encounters a dendritic cell presenting an antigen?
Activation –> Antigen recognition
Extravasation of T cells into lymph nodes
Similar to neutrophil extravasation
Entering endothelium
What does the protein L selectin (CD62L) allow?
Engagement with CD34 on endothelial cells of the high endothelial venule
Engagement with CD34 allows?
Initial binding and rolling along the endothelium
What does LFA-1 do?
Binds ICAM on the lymphocyte endothelial vessels allowing them to migrate across the endothelium
What happens to ICAM during inflammation?
It is upregulated to encourage T cells to migrate into those lymph nodes
What is antigen presentation?
Display of peptides in the MHC I or II proteins such that the T cell receptor can attempt to bind them
Role of dendritic cells
- Professional APCs
- Range of migratory and tissue resident variety
- Migrate out of the site of inflammation
Dendritic cell migration
- Via afferent lymph into lymph nodes
- To interact with T cells
What does CD stand for?
Cluster of differentiation
What CD do T cells uniquely express?
CD3
What CD do B cells uniquely express?
CD19
