Lymphoid Anatomy Flashcards
central lymphoid organs
thymus and bone marrow
peripheral lymphoid organs
adenoid, tonsil, lymph nodes, appendix, spleen, mucosal
B and T cells originate where
bone marrow
B cell mature where
bone marrow and are continually produced even in adults
where do T cell mature
thymus-slows down as individuals age but T cell numbers are maintained outside the central lymphoid organs
adaptive immunity occurs when
a lymphocyte meets its corresponding antigen in the peripheral lymphoid tissue
purpose of lymphoid tissue
Supports lymphopoiesis
Supports development of incredibly diverse repertoire of antigen-specific lymphocytes
Critically important for both central & peripheral tolerance
Provides sustaining signals for lymphocyte survival
central lymphoid tissue purpose
Responsible for lymphopoiesis
Responsible for central tolerance
B cells: Bone Marrow
T cells: Thymus
peripheral lymphoid tissues purpose
Mixture of B & T cells
Supports circulating lymphocyte survival
Activation of naïve lymphocytes
Peripheral Tolerance
Stromal cells
Stromal cells in the bone marrow, are critically important to B cell development. Provide maturation factors such as FLT3 ligand, IL-7, Stem-Cell Factor (SCF) & CXCL12
final stage of immature B cells developing to mature B-cells occurs where?
peripheral lymphoid organs
Central Tolerance
immature B cells in the BM are tested for reactivity to self antigens or auto reactivity and are eliminated if autoreactive
thymus cortex
the outer cortical region; contains only immature thymocytes & scattered macrophages; most t-cell development occurs here
thymus medulla
the inner region; more mature single positive thymocytes, dendritic cells & macrophages
lack of Thymus
no T cell development despite lymphoid progenitors
young vs old thymus
The thymus is fully developed at birth
Rate of T-cell production is greatest before puberty
After puberty, the thymus begins to shrink & the production of new T cells is lower but not entirely absent
when does the beta chain rearrangement of the T-cell receptor take place
during the double negative phase
when does the alpha chain rearrangement take place
during the puble positive phase
T-cell development relays on
timely expression of various surface and signaling molecules
thymic cortal 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 process that express both MHC I and MHC II on their surface.
corticomedullary junction of the thymus
where the t cell progenitors enter
positive selection
if the double positive T cell does recognize self-peptide;self-MHC complexes, than it will drop one of the co-receptors and become either CD4+ or CD8+ single positive T-cells and migrate to the medulla
Negative selection
If the single positive T-cell recognizes self-peptide:self-MHC too strongly, then it will undergo apoptosis. If it does not it will be exported from the thymus to the periphery
central tolerance
98% of thymocytes that develop in the thymus also die in the thymus by apoptosis. includes positive and negative selection
