Lymphoid Organs PDF

Lymphoid organs and system 1  Lymphoid Organs lymphoid tissues (Primary lymphoid organs) Thymus, B.M., (in embryonic course comprise Yolk sac, Liver and spleen) lymphoid tissues (Secondary lymphoid organs) Lymph nodes, Liver Spleen, Lymphocytes, NK,...

Lymphoid organs and system 1  Lymphoid Organs lymphoid tissues (Primary lymphoid organs) Thymus, B.M., (in embryonic course comprise Yolk sac, Liver and spleen) lymphoid tissues (Secondary lymphoid organs) Lymph nodes, Liver Spleen, Lymphocytes, NK, MONO, MQ, DCs, NEUT, EOS,….. Immune response sites (Tertiary lymphoid organs) Any where that immune system fight with organisms 2 Th, CD3+, CD4+ Tc, CD3+, CD8+ B , CD19+, CD20+ NK, CD16+, CD56+ Self- renewing MQ, CD14+ DC, CD11c+ Production of naïve (in mice 1-3 months) lymphocyte is under equilibration with lymphocyte death with apoptosis (homeostasis) 3 4 T Cells ◼ 80% of circulating lymphocytes ◼ Some of the types: ❑ Cytotoxic T cells: attack foreign cells or body cells infected by viruses (“cell-mediated immunity”) ❑ Regulatory T cells: Helper T cells and suppressor T cells (control activation and activity of B cells) ❑ Memory T cells: produced by the division of activated T cells following exposure to a particular antigen (remain on reserve, to be reactivated following later exposure to the same antigen) ◼ Memory T cells (CD44 high) CD45RO whereas Naive T cell express CD45RA receptor. 5 B Cells ◼ 10-15% of circulating lymphocytes ◼ Can differentiate into plasmocytes (plasma cells) when stimulated by exposure to an antigen ◼ Plasma cells produce antibodies: soluble proteins which react with antigens, also known as immunoglobulins (Ig’s) ◼ “Humoral immunity”, or antibody-mediated immunity ◼ Memory B cells: produced by the division of activated B cells following exposure to a particular antigen (remain on reserve, to be reactivated following later exposure to the same antigen) 6 NK Cells ◼ 5-10% of circulating lymphocytes ◼ Attack foreign cells, normal cels infected with viruses, cancer cells that appear in normal tissues ◼ Known as “immunologic surveillance” 7  What are T cells? ◼ Migrate from marrow and develop in thymus ❑ Have antigen receptors on PM = immunocompetent ◼ Mitosis produces clones ❑ Clonal deletion destroys self- reactive clones ◼ Good at destroying cells and stimulating B cells ❑ They do NOT secrete antibodies as B cells do ❑ T cell types movie 8  DC DC 9 ◼ T cells (helper and cytotoxic) “feel” cells ❑ Check for MHC (hotdog bun) ◼ MHC = major histocompatibility complex ◼ MHC-I on all cells ◼ MHC-II only on APCs ◼ HLA (human leukocyte antigen) group = MHC 10 Dendritic cells known as professional APC 11 12 Lymph Organs: Lymph nodes Spleen Thymus Peyer’s patches Tonsils Red Bone Marrow Appendix 13  The Lymphatic System Part of the immune system that consists of 2 independent parts: 1. meandering network of lymphatic vessels 2. various lymphoid tissues and organs Lymphatic system is located within loose connective tissue systems of the body 14 Lymphatic System ◼ Consists of three parts 1. A network of lymphatic vessels (lymphatics) 2. Lymph - a fluid 3. Lymph nodes 15 Lymphatic Capillaries ◼ Absent from teeth, bone marrow and the CNS (Brain lacks immune system generally) ◼ Lacteals: specialized lymph capillaries present in intestinal mucosa ❑ Absorb digested fat and deliver fatty lymph (chyle) to the blood 16 Lymphatic System ◼ One way system: to the heart ◼ Return of collected excess tissue fluid ◼ Return of leaked protein ◼ “Lymph” is this fluid ◼ Edema results if system blocked or surgically removed 17 ◼ Lymph capillaries ❑ Have one way minivalves allowing excess fluid to enter but not leave ❑ Picks up bacteria and viruses as well as proteins, electrolytes and fluid (lymph nodes destroy most pathogens) 18 Dynamics of Capillary Exchange 19  Regional Internal jugular vein lymph nodes: Cervical nodes Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Axillary nodes Thoracic duct Cisterna chyli Aorta Inguinal nodes Lymphatic collecting vessels Drained by the right lymphatic duct Drained by the thoracic duct (a) General distribution of lymphatic collecting vessels and regional lymph nodes. 20 Figure 20.2a  arteriole blood capillaries lymphatic capillaries venule lymphatic vessel 21  Fig. 22.04 Systemic Circulation 22 HEV; High endothelia venule that present in Lymph node and Pier patches but not in spleen. 23 What does the lymphatic system do? ◼ Return interstitial fluid ❑ Capillaries only reabsorb 15% ❑ Funneled into subclavian veins ◼ Absorb and transport lipids from intestines ◼ Generate and monitor immune responses ◼ lymphatic system movie 24 Lymphatic System: Functions ◼ Returns interstitial fluid and leaked plasma proteins back to the blood ❑ Once interstitial fluid enters lymphatics, it is called lymph ◼ Together with lymphoid organs and tissues, provide the structural basis of the immune system ◼ Antigen concentration and focusing √ 25 Lymphatic Capillaries ◼ Similar to blood capillaries, except ❑ Very permeable (take up cell debris, pathogens, and cancer cells) ❑ Endothelial cells overlap to form one-way minivalves, and are anchored by collagen filaments, preventing collapse of capillaries 26  Lymphatic vessels Form a 1-way system in which lymph fluid flows only toward the heart Vessels are similar to capillaries, but very permeable. They occur everywhere blood capillaries occur. 27  Lymph Transport lacks pump for circulation relies on activity of skeletal muscles and pulsation of nearby arteries for movement of fluid 3L of lymph enters blood stream every 24 hrs proteins easily enter lymphatic system uptake of large particles such as cell debris, pathogens, and cancer cells lymph nodes where it is cleansed of debris and examined by cells of the immune system. 28  Lymph node anatomy (FDC) Cytokine determined anatomical distribution of immune cells in L.N. and CCR7 helps DC and Lym and CXCR5 for Ln-B to transfer to lymph nods. Cell migration through HEV carried out in Cortex area. LT-B is important in lymph node formation. 29  What is in the lymphatic system? ◼ Lymph nodes ❑ Filters lymph fluid for antigens, bacteria, etc. ◼ B-lymphocytes made here ◼ Some T-lymphocytes and macrophages congregate ◼ Afferent (more) and efferent (less) vessels ❑ lymph fluid exits through hilum ❑ Common site for cancer—Why? ◼ Hodgkin’s lymphoma: lymph node malignancy ❑ Etiology unknown ◼ Non-Hodgkin’s lymphoma: all other cancers of lymphoid tissue ❑ Multiplication/metastasis of lymphocytes ❑ 5th most common cancer 30 The Lymphatic system 31 32 33  Regional Internal jugular vein lymph nodes: Cervical nodes Entrance of right lymphatic duct into vein Entrance of thoracic duct into vein Axillary nodes Thoracic duct Cisterna chyli Aorta Inguinal nodes Lymphatic collecting vessels Drained by the right lymphatic duct Drained by the thoracic duct (a) General distribution of lymphatic collecting vessels and regional lymph nodes. 34 Figure 20.2a After Antigen stimulation Flow rate to Lymph node increase more than 20 times. 35 36 37  Spleen ◼ Largest lymphoid organ ◼ Served by splenic artery and vein, which enter and exit at the hilus ◼ Functions ❑ Site of lymphocyte proliferation and immune surveillance and response ❑ Cleanses the blood of aged cells and platelets, foreign matter, bacteria, viruses and debris ❑ Stores breakdown products of RBC ◼ e.g. iron ❑ Erythrocyte production in fetus (normally ceases after birth) 38 Structure of the Spleen ◼ Two distinct areas ❑ White pulp around central arteries ❑ Mostly lymphocytes on reticular fibers and involved in immune functions ❑ Red pulp in venous sinuses and splenic cords ◼ Rich in macrophages for disposal of worn-out RBCs and bloodborne pathogens 39 40  Splenic artery Splenic vein Hilum (a) Diagram of the spleen, anterior view (b) Diagram of spleen histology White pulp; Adjacent to artery and contain PALS, Follicle and marginal zone Red pulp; Adjucent to tiny venule and contain RBC, MQ, DC, Ln, and plasmacell. Red pulp area contains MQ that deleted opsonized bacteria such as Meningococcal, Pneumonococci 41  Thymus Located: on top of heart Secretes hormones thymosin and thymopoeitin Causes T-lymphocytes to function against specific pathogens in the immune response (called immunocompetent) Most active during youth; it  in size during childhood, by old age, it's mostly been replaced by fibrous and fatty connective tissue 42 Thymus ◼ Differs from other lymphoid organs in important ways ❑ It functions strictly in T lymphocyte maturation ❑ It does not directly fight antigens ◼ The stroma of the thymus consists of star- shaped epithelial cells (not reticular fibers) ◼ These thymocytes provide the environment in which T lymphocytes become immunocompetent 43 Thymus ◼ Thymic lobes contain an outer cortex and inner medulla ◼ Cortex contains densely packed lymphocytes and scattered macrophages ◼ Medulla contains fewer lymphocytes and thymic (Hassall’s) corpuscles involved in regulatory T cell development 44 Thymic (Hassall’s) corpuscle Medulla Cortex 45 Figure 20.7 46  Immune system in skin Langerhans cells after antigen capture immigrate to derma area. IEL contain TCD8+ cells. 47 MALT ◼ Mucosa-associated lymphatic tissue, including ❑ Peyer’s patches, tonsils, and the appendix (digestive tract) ❑ Lymphoid nodules in the walls of the bronchi (respiratory tract) ◼ Protects the digestive and respiratory systems from foreign matter 48  Mucosal Immune system (Three compartment) In mice 50% and in human 10% of such T cells are γδCD8+ A B Most T cells in lamina C properia are activated CD4+ 49 Aggregates of Lymphoid Follicles ◼ Peyer’s patches ❑ Clusters of lymphoid follicles ❑ In the wall of the distal portion of the small intestine ❑ Similar structures are also found in the appendix ◼ Peyer’s patches and the appendix ❑ Destroy bacteria, preventing them from breaching the intestinal wall ❑ Generate “memory” lymphocytes 50 Tonsils ◼ Simplest lymphoid organs ◼ Form a ring of lymphatic tissue around the pharynx ❑ Palatine tonsils—at posterior end of the oral cavity ❑ Lingual tonsils—grouped at the base of the tongue ❑ Pharyngeal tonsil—in posterior wall of the nasopharynx ❑ Tubal tonsils—surrounding the openings of the auditory tubes into the pharynx 51  Tonsils Prevent pathogens in respiratory tract and digestive tracts from penetrating mucous membrane lining. The nature of immune response in moth is differ and comprise high titer Antibody response and tolerance in T cell response. 52 Tonsils ◼ Contain follicles with germinal centers ◼ Are not fully encapsulated ◼ Epithelial tissue overlying tonsil masses invaginates, forming tonsillar crypts ◼ Crypts trap and destroy bacteria and particulate matter 53  Pharyngeal tonsil Palatine tonsil Lingual tonsil Tonsil Tonsillar crypt Germinal centers in lymphoid follicles 54 Figure 20.8 Lymphocyte recirculation: ◼ Lymphocyte homing (for specific sub-population) is selective process for specific tissue not for else (Antigen dependent). ◼ Migration of Naïve T cells is differ from effector and memory T cells. ◼ Cell migration is under Adhesion molecule control (Three molecular family, selectins, Integrins and super Igs). 55 HEV; High endothelia venule that present in Lymph node and Pier patches but not in spleen First and loose binding with Selectins and strong binding with Integrins. Naïve T cell express L-selectin but Effector T cells more P and E selectin and CD44 and Expression of CCR-7 decreased in activated T cells. 56 ◼ Ln B express CXCR-5 for migration into Lymph nodes and after stimulation loss it and export from Follicle and migrate to T cell area and express integrins for migrations. 57 58 Thanks 59