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Molecular medicine Immunology 2

Molecular medicine Immunology 2. Tissues of the Immune system ht tps://medicine.tcd.ie/immunology/student-area/index.php. Learning objectives. Key role of certain tissues in immune system (IS) The thymus - site of T cell education Bone marrow - source of cells of IS

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Molecular medicine Immunology 2

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  1. Molecular medicine Immunology 2 Tissues of the Immune system https://medicine.tcd.ie/immunology/student-area/index.php

  2. Learning objectives • Key role of certain tissues in immune system (IS) • The thymus - site of T cell education • Bone marrow - source of cells of IS • Lymph nodes - site of immune reactions • NB - cells of IS operate in tissues, not in blood

  3. Lymphatic circulation

  4. Lymphatic circulation Third network of circulation Function - • Collects fluid from tissues • Lymph passes through chain of lymph nodes • Lymphatic vessels drain to large ducts e.g. thoracic duct • Ducts drain into subclavian veins

  5. Thoracic duct

  6. Lymphatic circulation • High content of lymphocytes • If lymph is drained from animals - lymphocyte count drops • If the lymphatics are blocked - fluid collects in tissues - “ lymphoedema ” Also • Fat is absorbed from intestine via lymphatic

  7. Swelling due to blocked lymphatics Damaged caused by radiation therapy, axilla

  8. Antigen delivery to lymph nodes

  9. Lymphatic circulation Immune response - • Antigen brought to lymph nodes - via lymph draining to nodes • Carried by antigen presenting cells e.g. dendritic cells • Lymphocytes stimulated by antigen in nodes • stimulated lymphocytes enter blood and circulate

  10. Lymphoid tissues

  11. Lymphoid tissues

  12. Lymphoid tissues Central • Bone marrow • Thymus • Bursa

  13. Lymphoid tissues Central • Bone marrow • Thymus • Bursa Peripheral • Lymph nodes • Spleen • Unencapsulated -appendix, tonsil, adenoids, Peyer’s patches

  14. Lymph nodes in neck

  15. Cancer - enlarged nodes

  16. Lymph nodes in axilla

  17. Cancer spread to lymph node Cancer cells “secondaries” or metastasis

  18. Lymph nodes in groin

  19. Bone marrow - cell origin

  20. Bone marrow - cartoon

  21. Bone marrow biopsy

  22. Bone marrow - what happens ? • generation of cells of IS and other cells - RBC, platelets • location of B cell maturation “bursa” in humans? • site of antibody production by plasma cells

  23. Damage due to cancer therapy • Chemotherapy • Radiation therapy Cause damage to bone marrow • Cell production reduced - neutrophils • Antibody production impaired

  24. Thymus - human

  25. Thymus - chicken

  26. Thymus 1. Location • Behind sternum - over heart • Bi-lobed • Lobules - 2 zones • Outer zone = cortex • Inner zone = medulla

  27. Thymus structures

  28. Thymus - histology

  29. Thymus 2. Cortex • Immature “pro-T” cells arrive here • Learn function of T lymphocytes • Densely cellular • 90% of cells die - lymphocyte graveyard ! • Surviving cells migrate to medulla

  30. Thymus - cartoon

  31. Thymus 3. Medulla - • mature lymphocytes migrate from cortex - cells then enter into blood circulation • Hassal’s corpuscles - characteristic structure of medulla, function unknown • Thymus atrophies after puberty - BUT continues to produce lymphocytes to end …..

  32. Thymus - chicken

  33. Bursa in humans • No identified equivalent of bursa • Bone marrow may carry out function of bursa • Maturation of pro-B cells in this site

  34. Lymph node - cartoon Alberts et al.

  35. Lymph node - histology Lymphoid follicles

  36. Lymph nodes 1. • Distributed throughout body • Linked by lymphatics • “afferent” lymphatics - drain to nodes • “efferent” lymphatics - drain from nodes • Blood supply - arterial, venous • Capsule

  37. Lymph nodes 2. Structure - cortex and medulla • Cortex - distinct T and B cell areas • B cells found in round structures - lymphoid follicles • Follicles enlarge after antigen stimulation • Stimulated B cells - migrate to medulla - antibody producing “plasma cells”

  38. Lymph nodes 3. T cell area in cortex • Surround lymphoid follicles • Stimulated T cells migrate to medulla and enter circulation Other cell populations • Antigen presenting cells - dendritic cells, macrophages

  39. Spleen

  40. Spleen - cartoon

  41. Spleen - histology Phagocytic area Lymphocyte area

  42. Spleen 1. Location • Under left rib cage • Blood supply - very vascular • Accidents - splenectomy Function • Phagocytic organ - removal of dying cells • Lymph node type function • Storage - platelets

  43. Spleen 2. Lymph node area • “white pulp” - 20% of spleen • Distinct T and B follicular areas • Respond to circulating antigen - important in response to certain bacteria • “Red pulp” area - phagocytic cells, storage of other cell types

  44. Spleen 3. “Red pulp” area - phagocytic cells, storage • remove particulate matter • graveyard for aged or damaged RBC, white cells, platelets • reservoir - rapid source of platelets

  45. Other lymphoid tissues • Tonsils • Appendix • Adenoids • Peyer’s patch • These tissues have lymph node like structure and function but no capsule

  46. Lymphocyte collections in organs • Gut • Lung • Liver • Placenta • Etc.

  47. Gut lymphocyte structures

  48. Events in lymphoid tissue • Immune response happens here • Metastasis - cancer cells can spread to nodes • Circulating lymphocytes ‘visit’ nodes - to see if specific antigen has arrived here • Lymphocytes may rest in nodes - memory cells

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