Week 4- Lymphoid Tissues Flashcards
What are the primary lymphoid tissues?
Bone marrow, thymus and fœtal liver
What are the 2 hallmarks of primary lymphoid tissues?
- Specificity- wide range of specific B and T cells
2. Memory- rapid response on second exposure
Describe the characteristics of the bone marrow
Main site of haematopoeisis but not in a foetus (location is red bone marrow), replaced by fat as we get older (yellow bone marrow)
Describe the route by which NK cells arise
Haemopoeitic stem cell goes to lymphoid progenitor goes to NK cell
Describe the route by which B cells arise
Haemopoeitic stem cell goes to lymphoid progenitor goes to B cell progenitor which go to the spleen to mature
Describe the route by which T cells arise
Haemopoeitic stem cells goes to lymphoid progenitor goes to T cell which can develop into one of 2 types: helper or cytotoxic
What is an individuals repertoire?
The collection of B and T cells that they have
What is the thymus?
Where immature T cells go to mature
How is selection of T cells in the thymus carried out?
At first T cells are double negative (not CD4 or CD8)
- Positive selection: is the receptor functional
- Negative selection: is the cell self or non self (if it’s self it should be made to undergo apoptosis)
- Final selection or exit (now its CD4 or CD8)
What happens to the thymus as we age? What is the technical term for this
It gets smaller, as does the no of T cells we have. Known as thymic involution
What is the main role of secondary lymphoid tissues?
To find the specific T cell against a pathogen
What are the main secondary lymphoid tissues?
Spleen, lymph nodes, appendix, mucosal tissues
Where can secondary lymphoid tissues be found and what systems are they connected to?
They are found all over the body and connected to blood the lymphatic system and blood so they can scan all antigens
Describe the general structure of lymph nodes
They have distinct B and T cell zones with afferent and efferent vessels. They have connections to lymphatic vessels and arterial and venous connections.
What do lymph node T cell zones contain and what is the function?
They contain fibroreticular networks that retain T cells and make chemokines to allow T cells to migrate
What do lymph node B cell zones contain and what is the function?
Follicular dendritic cells that make chemokines to attract B cells and capture immune complexes
Describe the general features of the spleen
Has afferent and efferent vessels, red and white pulp, very heavy connection to blood as it scans the blood thoroughly, also makes RBCs
What are Peyer’s patches? Describe where they are found and their role
They are found underneath the epithelium of the ileum in the small intestine, they contain germinal centers where B cells undergo selection and mutation to form antibodies with high affinity
Where are germinal centers found in the body?
Peyers patches and tonsils
How are T cells extravased into lymph nodes?
They bind to selectin, activation of CD34 allows them to roll along the epithelium, then LFA-4 binding means they can migrate into the lymph node
