Lymphoid tissues Flashcards
What are lymphoid tissues?
Organs in which lymphocyte production, maturation + differentiation occur
What processes occur in lymphoid tissues?
Reactions to antigens + proliferation
Distinguish b/w primary + secondary lymphoid tissues
Primary = where lymphocytes are generated + matured Secondary = where lymphocytes interact with APCs
Give examples of primary lymphoid tissues
Bone marrow, Thymus, Bursa of Fabricus (birds), Ileal Peyer’s patch, appendix
Give examples of secondary lymphoid tissues
Lymph nodes, MALT, Spleen
What does MALT stand for?
Mucosal- Associated Lymphoid Tissue
Explain the role of the thymus in the immune system
Lymphocytes produced by bone marrow are transported to thymus in blood where T cell maturation + selection occurs
What cells does the thymus contain?
Thymocytes (immature T cells), mature T cells, epithelial cells, dendritic cells, Hassall corpuscles
Describe the cortex of the thymus
- densely populated w/ lymphocytes
- some macrophages
- thymocytes mature to adult T cells in cortex
Describe the medulla of the thymus
- Adult T cells meet APCs
- Thymic selection occurs
- Survivors go into circulation + move through secondary lymphoid tissues
What do macrophages found in the cortex of the thymus do?
removed thymocytes that have undergone apoptosis
Describe the passage of thymocytes through the thymus
- thymocytes enter via cortex + migrate through medulla
- various cell contacts result in 95% of T cells being eliminated
- removes most self-reactive T cells
Describe lymph node surveillance
- <10% lymphocytes in lymph node enter via lymph
- >90% come from circulation + enter via high endothelial venules
Where are MALT found?
GI tract, respo tract, Peyer’s patches, appendix, tonsils
Where does MALT operate?
In very dense areas of lymphocytes- around bronchial lumens, lamina propria + mucosa of large/ small intestine
What are Peyer’s patches + what role do these play in the immune system?
- present in ileal mucosa of small intestine
- germinal centres prominent at sites of Ab production
- detect Ags that diffuse across intestinal epithelia via M cells
