Functional Lymphoid Anatomy Flashcards
(59 cards)
Name 5 sites of secondary/peripheral lymphoid tissue
Adenoids Tonsils Lymph Nodes Peyer's patches (mucosal tissue) spleen
Name the two central/primary lymphoid tissues
Bone marrow
Thymus
What occurs in central vs peripheral lymphoid tissues?
Central: generates B and T cells, responsible for central tolerance
Peripheral: Primes B and T cells into effector cells (supports circulating lymphocyte survival, peripheral tolerance, activation of naive T cells)
Where do B cells and T cells originate? What are they derived from?
Bone Marrow- all lymphocytes are derived from hematopoietic stem cells.
What are stromal cells?
Stromal cells (in the bone marrow) provide critical signals (cytokines) that direct the developmental program of the progenitor cells and eventually b-cells
ie. they are critical for B-cell development
Where do the final stages of development of B cells occur (from naive to effector cells)
Peripheral lymphoid organs
What is central tolerance for B cells?
Immature B cells in the bone marrow are tested for reactivity to self antigens, or autoreactivity, and are eliminated (apoptosis) if they are autoreactive.
Immature B cells that have no strong reactivity to self are allowed to mature
What happens to immature B cells that are not self-reactive? Where do they go next?
Immature B cells that have no strong reactivity to self are allowed to mature. They leave the marrow via sinusoids that enter the central sinus and are carried by the venous blood supply to the spleen
What is the fate of a B cell that reacts to multi-valent self molecules?
1) Rescue by receptor editing -or-
2) Death via apoptosis
What is the fate of a B cell that reacts to soluble self-molecule?
Migrates to the periphery but becomes anergic
What is the fate of a B cell that reacts with low affinity to soluble self molecule (no cross linking occurs)
Migrates to the periphery as an autoreactive cell
Germinal centers and lymphoid follicles are unique to what class of lymphoid organs (central or peripheral)?
Peripheral only
What cells are found in the cortex of the thymus?
Immature thymocytes and scattered macrophages
What cells are found in the medulla of the thymus?
more mature thymocytes (single positive), dendritic cells and macrophages
What is the fate of 98% of thymocytes?
Death by apoptosis and removal by cortical macrophages
What survival factor is required for the survival of thymocytes in the thymus?
IL-7, secreted by cortical epithelial cells.
In the absence of IL-7, thymocytes will die
Describe the rate of production of new T cells in the thymus throughout a persons’ lifetime
The development of new T cells in the thymus slows down in mature individuals.
The development of new T cells is greatest before puberty
How are T cells numbers maintained throughout a person’s life if the generation of new T cells in the thymus slows down?
1) Long-lived individual T cells
2) Division of mature T cells outside the central lymphoid tissue
Where does most of the T cell development occur?
thymic cortex
What occurs at the corticomedullary junction of the thymus?
T cell progenitors enter
Describe the thymic cortical stroma
Network of epithelia where the T cell precursors reside; provides unique microenvironment for T cell development (like B cell stromal cells); has epithelial cells with long branching processes that express both MHC Class I and II molecules on their surface.
T cell development:
Where do T cell progenitors from the bone marrow enter the thymus? Where do the cells go within the thymus?
Progenitors from the bone marrow enter at the corticomedullary junction and migrate to the outer cortex
T cell development:
Following entry into the thymus, what happens to cells at the outer cortex/subcapsular region of the thymus?
Large immature double-negative thymocytes proliferate vigorously
What are markers are double-negative T cells missing?
T-Cell Receptor complex: CD3
T cell Co-receptor: CD4 and CD8
