Lect. 11 lymphatic tissues


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Lect. 11 lymphatic tissues

  1. 1. Lecture # 9
  2. 2. Cells, tissues and organs that monitor body surfaces and internal fluid compartments;  react to (+) potentially harmful antigenic substances (infectious microorganisms, viral entities, toxins, foreign cells and tissues, & normaL cells that transformed into cancer cells) recognized as ("non-self“).
  3. 3. - Organs in which immune cells undergo maturation, and/or differentiation, and proliferation.
  4. 4.  Bone marrow and Thymus  Sites of immune cell maturation and differentiation.  Tissues in which lymphocytes are generated and differentiate into mature naïve B cells and T cells.  Cells here do not come into contact with an antigen.
  5. 5. Primary site of hematopoiesis. Immune cells arise from progenitors in the bone marrow. Site for B cell maturation.
  6. 6. Bone Marrow  Rearrangement of genes that encode the B cell receptor that will recognize foreign antigen, but not foreign molecules.  B cell receptor – membrane immunoglobulins  Screening process – self-reactive B cells are eliminated  Naïve, mature B cells (functional): released in the bone marrow.  seed the peripheral lymphoid tissues  circulate in immunosurveillance
  7. 7. Thymus  Flat, bilobed organ situated above the heart and below the thyroid gland.  Encapsulated organ
  8. 8. It increases in size until it reaches its peak development during adolescence. Becomes smaller with age. A B
  9. 9. Pre-T cells from the bone marrow migrate to the cortex to undergo maturation. The thymus is where T cells are "educated" to distinguish self from nonself.
  10. 10.  Construction of T cell receptor (TCR) - gene rearrangement (a random process).  Thymic Selection: a screening process  only the T cells with TCRs that can recognize antigens (TCRs beneficial to the host) will survive and mature.  Mature T cells leave the thymic medulla, enter the blood stream.  Seed the secondary lymphoid tissues  circulate in immunosurveillance.
  11. 11. Table 1. Approximate Percentage of B and T Lymphocytes in Lymphoid Organs (Junquiera et al., 2005) Lymphoid Organ T Lymphocytes, (%) B Lymphocytes, (%) Thymus 100 0 Bone marrow 10 90 Spleen 45 55 Blood 75 35
  12. 12. Lymph nodes, spleen, tonsils, Peyer’s patches, MALT, and cutaneous immune system Exposure to antigens initiates immune responses in the secondary lymphoid tissues.
  13. 13.  Secondary lymphoid tissues provide a place where lymphocytes can talk to each other, and to other cells.  They provide an environment for antigen focusing, where lymphocytes can 'study' an antigen, and sharpen up the immune response by clonal expansion and affinity maturation.  They provide a home for lymphocytes, where they can be available when they're needed.
  14. 14. LYMPH NODES Small encapsulated structures located at the junction of the main lymphatic tracts. Serve as central collecting points for lymph fluid from adjacent tissues; mainly functions for filtration. BONE MARROW APPENDIX THYMUS BRONCHUS ASSOCIATED LYMPHOID TISSUE TONSIL Axillary node Intercostal node SPLEEN PEYER’S PATCHES Lumbar node Iliac node Inguinal node Cervical node
  15. 15. LYMPH NODES Filtering function - to trap antigens and cells containing antigen that flow into them via afferent lymphatics. To provide a site for clonal expansion of lymphoid cells recruited from the millions of cells that enter and leave via various routes.
  16. 16. Lymph fluid  fluids and low-molecular-weight solutes drained from the tissues (by passing out of blood vessel walls and into the interstitial spaces between cells).  flowing through thin-walled lymphatic vessels.
  17. 17. Afferent lymphatic vessel: the entrance of lymph fluid which contains the antigens and cells Efferent lymphatic vessel: where drained lymph fluid along with lymphocytes exit; connected with the thoracic duct and venous system. Subcapsular sinus – lined with macrophages where antigen processing takes place. Node: cortex, paracortex and medulla
  18. 18.  Cortex – mostly B cells  Paracortex – mostly T cells; APCs; HEV (high endothelial venules)  Interfollicular region – T cells; APCs  Medulla – less densely populated area but contains some T cells, B cells and macrophages.
  19. 19.  Primary follicles – small rounded masses of cells which are inactive due to absence of antigenic stimulation. Contains mature, resting B cells  B cells that are not yet stimulated by an antigen  Secondary follicles – larger masses or follicles containing germinal centers generated during an encounter with antigens carried by the lymph.  B cells are stimulated / activated by antigens
  20. 20. • a mass of activated B cells • site where B cells proliferate and differentiate into plasma cells. Plasma cell-release antibodies Lymphocyte B cell Plasma cell
  21. 21. SS – subcapsular space T – trabecula
  22. 22.  the largest secondary lymphoid organ  located in the upper left quadrant of the abdomen just below the diaphragm  a large discriminating filter  filters out old and damaged cells and foreign antigens from the blood
  23. 23.  makes up more than one-half of the total volume;  its function is the destruction of old red blood cells – by splenic macrophages  blood flows from the arterioles into the red pulp and exits through the splenic vein  red matrix; composed of sinusoids and splenic cords of cells (cords of Billroth); vascular areas
  24. 24.  contains the lymphoid tissue  arranged around arterioles in a periarterial lymphatic sheath (PALS)  with lymphoid follicles attached; PALS and lymphoid follicles are surrounded by a marginal zone.
  25. 25.  Periarterial lymphatic sheath (PALS) • Contains primarily T cells; also macrophages, plasma cells and granulocytes. • Lymphocytes enter and leave this area by means of the many capillary branches that connect to the arterioles  White marginal zone • contains dendritic cells and macrophages; CD+4 T cells and B cells
  26. 26.  MALT (mucosa-associated lymphoid tissue) 1. GALT – gut-associated lymphoid tissue  Peyer’s patches 2. BALT – bronchus-associated lymphoid tissue  Tonsils Exhibit primary and secondary lymphoid nodules
  27. 27.  consist of diffusely distributed lymphoid cells and follicles that underlie all regions coated with mucosa.  has similar immune tissue components as the lymph nodes and spleen.  the main difference of MALT: immune tissue components are not encapsulated; scattered diffusely.
  28. 28. - involved in defense against pathogens that may be colonizing the gut. Esophagus
  29. 29.  Payer’s patches: represents a specialized type of MALT; form larger aggregates of lymphoid nodules (colon, appendix, ileum)
  30. 30. Notice the germinal center where B-cells proliferate. These are a major source of antibody production.
  31. 31.  small masses of macrophages and lymphoid tissue found in the mucous membrane lining of the oral and pharyngeal cavities  Function: to respond to pathogens entering the respiratory and alimentary tracts Palatine tonsil
  32. 32. GC- Germinal center
  33. 33. The pharyngeal tonsil is distinguished from the palatine by the presence of pseudostratified columnar epithelium (arrows).
  34. 34.  Cutaneous-associated lymphoid tissue  Immune cells present in the epidermis and dermis of the skin  Activated Keratinocytes – produce a number molecules that play an important role in host defenses  Langerhan’s cells – APC’s in the skin  T cells – uniquely positioned to combat any antigens that enter through the skin