Functional Lymphoid Anatomy Flashcards
What are the central (primary) lymphoid organs?
Bone Marrow (b-cells)
Thymus (t-cells)
–>lymphopoiesis
–>central tolerance
What are the peripheral (secondary) lymphoid organs?
Lymph Nodes, Spleen, Mucosal Associated Lymphoid Tissue
- ->activation of naive lymphocytes
- ->peripheral tolerance
What do stromal cells do?
provide signals that direct the development of progenitor cells and eventually b-cells
What is central tolerance?
Immature B-cells in the BM are tested for reactivity to self antigens
-eliminated if autoreactive
HOw do mature B-cells leave the marrow?
via sinusoids that enter the central sinus and are carried by the venous blood supply to the spleen
What is in the thymic cortex of the thymus?
outer cortical region
- contains only immature thymocytes and scattered macrophages
- most T-cell development occurs here
- double negative t-cells
What is the corticomedullary junction?
where T-cell progenitors enter
What is the medulla?
Inner region
-more mature, single positive thymocytes along with the dendritic cells and macrophages
What is the thymic cortical stroma?
network of epithelial where T cell precursors reside
- provides unique microenvironment for T-cell development
- has epithelial cells with long branching processes that express both MHC 2 and 1
What are the steps of T-cell development?
- double negative -proliferate vigorously and CD3 negative
- Receptor rearrangement –>CD3+ and CD4 CD8 double positive
- Positive Selection–>CD8 or CD4
- Negative selection: must not recognize self too much
Where do T cells encounter foreign antigens?
In the peripheral lymphoid organs
Does lymphoid tissue provide sustaining signals to lymphocytes that do not encounter their specific antigen immediately?
yes so they will continue to survive and recirculate
Are peripheral lymphoid tissues dynamic?
yes
B-cell follicles of a lymph node will expand during infections to form germinal centers and the entire lymph node enlarges
What is homing of lymphocytes and other cells to specific regions of peripheral tissues mediated by?
chemokines
What is lymph?
extracellular fluid from tissues
How do antigens get to the lymph nodes?
Free antigen or antigen on an APC travel from site of infection through the afferent lymphatic vessels into the draining lymph nodes
WHat happens once the antigen or APCs get to the lymph node?
antigen-specific lymphocytes are activated
- 1 week later, the activated lymphocytes and its clones leave via efferent lymphatic vessels
- to the bloodstream via the thoracic duct and back to the site of infection
What is steady-state?
naive lymphocytes that do not recognize their antigen leave via efferent lymphatics and recirculated until they meet their match or die
What are High Endothelial venules (HEV)?
How naive lymphocytes get into lymphoid
-located in paracortical areas
What are the follicles of the lymph node?
where B cells are located in lymph node
What is in the outer cortex of the lymph node?
follicles
What is the paracortical area?
- deep cortex where the T cells are diffusely scattered
- where free antigen gets trapped on resident DCs and macrophages
- where dendritic cells bring their antigens
- –>meeting spot for T cells and APCs so T cells can become activated
What are germinal centers?
where activated B cells undergo intense proliferation and differentiation into plasma cells with the help of T helper cells
-somatic hypermutation, and class switching
Is the spleen directly connected to the lymphatic system? What type of pathogens does it respond to?
no
collects antigens from the blood
-involved in immune responses to blood-borne pathogen (not tissue)
