Lynphoid Tissues Flashcards
What are the hallmarks of adaptive immunity?
Specificity and memory
To what extent are b and T cells specific?
Each cell has the ability to express only one type of cell receptor (BCR/TCR) that is unique. The DNA sequence that codes it is unique, as is the antigen it can recognise
The gene that encodes the TCR allows up to 10e15 different unique sequences
How do b and T cells make so many different antibodies?
B CELLS
The shape of the antibody is determined by the variable region. Diversity is generated in the early stages of development. There are multiple copies of V, D and J genes. These are rearranged. The heavy chain also has its own V and J genes. There are also additional nucleotides added between these genes by the enzyme TdT, changing the structure of the variable region. When a B cell binds the shape of the variable region can alter in a process called somatic hypermutation, randomly mutating the variable region.
T CELLS
These work in a similar way only they don’t have antibodies
What is primary lymphoid tissue?
Where lymphocytes are produced
Lymphopoiesis (b, T and natural killer cells)
Eg. Bone marrow, thymus, foetal liver
What makes up the adaptive immune response?
B and T cells
They have unique BCRs and TCRs
What receptors do T helper cells have?
CD4
What receptors do cytotoxic T cells have?
CD8
What happens to white cell production during infection?
Increased
Where are B cells and their repertoire produced?
In the bone marrow , however final maturation can occur in the periphery (eg spleen)
Where are T cells produced?
In the Thymus,
Migrate there from the bone marrow
How do T cells develop?
Stepwise.
An immature thymocyte undergoes positive selection in the vortex of the thymus.
Then negative selection occurs. Checks that the T cell doesn’t react to self antigens. If they do, they undergo apoptosis
Then final selection and exit
What happens to the thymus with age?
It’s output declines. The medulla is slowly replaced by adipose tissue
Why are secondary lymphoid tissues necessary?
1.5e9 T cells per L of blood
5L of blood in bod
7.5e9 in all blood
Blood only contains 2% of all T cells
So 7.5… x 50 = 3.75e11 T cells in total
However they may only be one T cell that has a specific receptor, so this must be transported to a place where it can induce a response
Remeber T cell repertoire is about 10^15 minimum
What is secondary lymphoid tissues
Where lymphocytes can interact with antigens and other lymphocytes
What are some secondary lymphoid organs?
Spleen
Lymph nodes
Appendix
Mucosal associated lymphoid tissues
These are distributed around the body.
Interconnected by the lymphatic system and the blood. They can be discrete organs, or distinct regions within a tissue. All highly organised structures.
They all bring cells into close proximity with antigens
What is the structure of lymph nodes?
Distinct zones for T cells and B cells
Have afferent and efferent lymph (in/out)
Also arterial and venous connections
Google a picture
What is the structure of the spleen
Similar to lymph nodes
Distinct B and T zones
Afferent and Efferent lymph
Arterial and venous connection
HOWEVER
More of an arterial connection
Unlike nodes, the whole organ is not specialised for this purpose. Only the white pulp of the spleen (which is inside the red pulp)
Where are epithelial barriers found?
Abundant Around the external facing membranes, such as the GI tract, and lining the oesophagus
The skin acts as the first line of defence as a physical barrier
Also abundant in areas that might have high levels of antigens. Such as peyers patches (specialised secondary lymphoid tissues) below the epithelium of the illeum of the small intestine
They are highly enriched with B cells and contain lots of germinal centres
What is a germinal centre
Anatomically restricted site where B cells undergo mutation and selection to generate high affinity antibodies
What is the structure of the tonsils (also a secondary lymphoid tissue)?
They encircle the oral and nasal cavity. Forming the waldeyer ring
They, like the peyers patches, have lots of lymphoid follicles which contain large germinal centres and lots of B cells
How do antigens and activated B and T cells get into the lymphatic system?
Drained from between tissue cells into the lymph
2-3 litres of lymph are returned to the blood every day via the superior vena cava
How often do naive T and B cells circulate?
Once every 24 hours
How does extravisation of naive T cells occur?
Look at inflammation, pretty much the same just different molecules involved
What are dendritic cells?
Professional Antigen presenting cells
