Lect. 11   lymphatic tissues
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  • 1. Lecture # 9
  • 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. - Organs in which immune cells undergo maturation, and/or differentiation, and proliferation.
  • 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. Primary site of hematopoiesis. Immune cells arise from progenitors in the bone marrow. Site for B cell maturation.
  • 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. Thymus  Flat, bilobed organ situated above the heart and below the thyroid gland.  Encapsulated organ
  • 8. It increases in size until it reaches its peak development during adolescence. Becomes smaller with age. A B
  • 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.  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. 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. Lymph nodes, spleen, tonsils, Peyer’s patches, MALT, and cutaneous immune system Exposure to antigens initiates immune responses in the secondary lymphoid tissues.
  • 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. 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. 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. 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. 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.  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.  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. • 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. SS – subcapsular space T – trabecula
  • 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.  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.  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.  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.  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.  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. - involved in defense against pathogens that may be colonizing the gut. Esophagus
  • 29.  Payer’s patches: represents a specialized type of MALT; form larger aggregates of lymphoid nodules (colon, appendix, ileum)
  • 30. Notice the germinal center where B-cells proliferate. These are a major source of antibody production.
  • 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. GC- Germinal center
  • 33. The pharyngeal tonsil is distinguished from the palatine by the presence of pseudostratified columnar epithelium (arrows).
  • 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