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37 Cards in this Set
- Front
- Back
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What are the 2 groups of lymphoid organ classifications?
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Primary
Secondary |
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What are the primary lymphoid organs sites of?
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B and T lymphocyte maturation
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Why is Lymphocyte maturation sequestered in a specific organ from the bone marrow?
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-To delete lymphocytes that FAIL to express Ag receptor
-To select for cells that express Ag receptors recognizing self Ag's appropriately |
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How does an Ag receptor that appropriately recognizes self Ags behave?
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-Neither too well
-Neither too poorly |
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What are the Primary lymphoid organs in humans?
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-Thymus
-Bone marrow |
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Where is the thymus located?
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Just above the heart
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How does the thymus size change with age?
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It gets smaller
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What happens when the thymus has to be removed during cardiac surgery on infants?
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There is increased susceptibility to infection
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What does this tell us about what goes on in the thymus?
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It is the site of Tcell maturation.
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What is the macroscopic anatomy of the thymus?
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-2 lobes
-surrounded by a capsule -Capsule makes septations -Divides it into lobules |
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What is each thymic lobule composed of?
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-Outer cortex
-Inner medulla |
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What cells enter the thymus from the bone marrow?
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Thymocytes
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Where are thymocytes most highly concentrated in the thymus?
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In the cortex (but they're also scattered in the medulla)
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What other cell type is found in the thymus?
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Epithelial cells
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What type of epithelial cells line the internal surface of the thymus capsule and septations?
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Subcapsular-Perivascular Epithelial cells (Type I)
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What does the Subcapsular epithelium function to do?
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Form a sort of blood-thymus barrier to modulate the entry of systemic antigens into the thymus.
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Does the subcapsular-perivascular epithelium contribute to the thymocyte development?
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It's important for it to be normal, but does not participate in functional interactions.
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What type are the Subcapsular perivascular epithelial cells?
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Type I
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What are Type II and Type II epithelial cells in the thymus?
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Cortical epithelial cells
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What is special about cortical epithelial cells?
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They have long dendritic processes that contact each other and developing thymocytes.
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What is found on the surfaces of the dendritic processes of cortical epithelial cells?
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Peptide/MHC complexes on bone marrow derived APC's
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What interacts with these antigen presentations?
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Developing thymocytes' TCRs
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What happens if the TCR binds the MHC/Ag complex poorly?
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It gets eaten up by cortical macrophages and spit out.
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What % of all developing thymocytes fail to bind well and thus meet their gory death?
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98%
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What happens if the TCR DOES bind the MHC/Ag complex well?
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It gets promoted to the medulla
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What is the process of promotion to the medulla called?
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Positive selection
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What are the 3 types of medullary epithelial cells?
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-Type IV and V medullary epithelial cells
-Type VI medullary epithelial cells |
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What is the function of the Type IV and V medulla epithel cells?
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Negative selection - present Ag/MHC to TCRs, and if they don't bind with high affinity they survive (not autoimmune).
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So what is the function of
-Positive selection -Negative selection |
pos - makes sure they bind
neg - makes sure they don't bind self |
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What do Type VI medullary epithelial cells do?
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Form Hassal's corpuscles and eat the thymocytes with TCRs that were too high affinity binding.
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What is the well described clinical pathology of the thymus?
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DiGeorge Syndrome
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What causes DiGeorge Syndrome?
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Failure of the 3rd and 4th pharyngeal pouches to develop
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What are the 3/4th pouches important for?
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-Thymic development
-Parathyroid development -Aortic arch development |
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What is the cause of DGS in 90-95% of patients?
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Hemizygous microdeletion of DNA from chromosome 12
12q11.2 |
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Does complete thymic aplasia develop in DGS?
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Only in about 1/2% of patients
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What are the most common problems in patients with DGS?
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Prolonged viral infections, 2ndary bacterial infections, and autoimmune disease.
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Is treatment needed for the majority of patients?
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no
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