Immune system and lymphoid organs

• What is the role of the immune system?

  immunity , integrated response , filtering/barrier systems , inadequate response
• What are the types of immunity?

  Innate: quick response , physical barriers , cells , cytokines , the complement system

  
  

  Adaptive: Slow response , adaption for a highly specific and strong response , immunological memory , cells
• What are the characteristics of the lymphocytes?

  agranula leukocyte , 5-6 micrometers , heterochromatic neucleus , little cytoplasm
• What are the types of lymphocytes?

  T lymphocytes , B lymphocytes , NK , gamma delta T
• What are the characteristics of T lymphocytes?

  Mature in the thymus , account for majority of circulating lymphocytes-cellular immunity, They have T cell receptor (TCR) and Co receptors (CD4 or CD8)
• What is the function of the T helper (CD4+)?

  Release cytokines , stimulates the response of other cells
• What is the function of the T cytotoxic (CD8+)?

  Destroy cells
• What are the characteristics of the t cell receptor?

  Membrane bound protein complex , specific for one epitope , each T lymphocyte clone.
• What is the mechanism of the TCR?

  The TCR binds to an epitope (small peptide) presented on the surface of the cells by the major histocompatibility complexes (MHC)
• What is the mechanism of the T helper (CD4+)?


  The TCR in T helper CD4+ lymphocytes interacts with MHC-II of antigen-presenting cells (APC)
• What are characteristics of dendritic cells?

  Cells with thin cytoplasmic extensions , antigen presenting cells , interphase between innate and adaptive immunity. Location: Abundant in skin , respiratory and digestive tracts
• Where do dendritic cells come from?

  Monocytes
• What is the mechanism of the T helper cell?

  1) Naive t helper cell attaches to epitope of MHC-2

  2) Activates into effector T cell which can be used to proliferation , cytokine production

  3) The CD4 T helper cell can differentiate into memory T cell
• What is the mechanism of the T helper cells becoming immunosuppressive T regulatory cells (TREGS)

  Effector CD4 differentiates into T regulatory cells (triggered by cytokines). T regulatory cell can differentiate into effector CD8 and dendritic cells.
• What is the mechanism of AIDS?

  Targets cells with CD4 receptors and kills cells
• What is the mechanism of the T cytotoxic (CD8+)


  The TCR in T cytotoxic CD8+ lymphocytes interacts with MHC-1 of all nucleated cells
• How does cancer disable the immune system?

  Cancer cells usually have a PDL (program cell death ligand) protein which initiates T cell death which spreads to other T cells through TCR
• What are the characteristics of B lymphocytes?

  Maturation in the bursa of fabricius

  Production of antibodies and differentiation into plasma

  Humoral immunity

  B cell receptor (BCR) : immunoglobulins antibodies bound to the plasma membrane
• What is the mechanism of B lymphocyte activation?

  Bacterium attaches to antigen of B cells which then ingests the antigen and display MHC 2 receptors that when bounded to TCR (CD4) it releases cytokine which then trigger B cells to differentiate into B memory cells and plasma cells
• Why do plasma cell present a dark blue colour in the cytoplasma?

  High number of RER
• What are some characteristics of natural killer cells (NK)?

  Cytotoxic: similar to cd8+ lymphocytes but are part of innate immunity , no TCR and no need to be activated by APC nor the cells.

  NK kill infected,tumor or transplanted cells
• What are some mechanisms NK cells recognize infected cells?

  1) FC antibodies

  2) Stress signals (membrane proteins)

  3) Lack of MHC 1
• What are the characteristics of macrophages?

  Phagocytosis of pathogens and damaged cells

  
  

  Receptors to recognize pathogenic antigens and altered proteins in damaged/aged cells

  
  

  Receptors for antibodies and complement proteins

  
  

  They are APC (MHC2)

  
  

  Inflammatory response (release cytokines)
• What is the integration of the immune response?

  Dendritic cells binds to antigen of pathogen which activates a proinflammatory cytokine release as we;; as CD4 activation into CD8 which produces B cells
• What are the divisions of the lymphatic system?

  Primary : Thymus , bone marrow

  
  

  Secondary: Lymph nodes , spleen , Mucosa associated lymphoid tissue (Malt: Tonsils , peyer patches , bronchi)
• What is the general histological structure of lymphoid tissue?

  Reticular fibers (type 3) , as well as dendritic cell , reticular support cells , lymphocytes , macrophages
• What is the life cycle of lymphocytes?

  formed in bone marrow which then goes to thymus where it transforms into a mature T lymphocyte which then goes into either lymph nodes , spleen , MALT
• What are the characteristics of the thymus?

  Two lobes subdivided in lobules , capsule (CT) , cortex (dark) and medulla (lighter)
• What is the histological organization of the thymic parenchyma?

  Lymphocytes (thymocytes) , epithelial reticular cells , macrophages , dendritic cells
• What is the function of epithelial reticular cells?

  Support (scaffold , regulatory cytokines) and maturation of T lymphocytes
• Why do many T lymphocytes die?

  Weak ability to bind antigens and react against self proteins
• What is the process of lymphocyte maturation?

  Immature T cells in cortex of thymus mature into mature T cells in medulla through the interaction with dendritic cells. Mature T cells leave the thymus through postcapillary venules
• What are the characteristics of the lymph nodes?

  600-700 lymph nodes intercalated in the lymphatic system , cluster of nodes under the arms , in the groin , neck and abdomen. Filtrate lymph
• Why is the lymph nodes important?

  Main centres for adapting to the immune response , maturation of B lymphocytes , transform B cells into plasma cells and memory B cells , lymph that leaves the lymph node enriched in antibodies will be delivered to the entire body.
• What is the structure of lymph node sinuses

  Endothelial cells with lymphocytes , fibroblastic reticular cells and macrophages
• Why does lymph slow circulation through the sinuses?

  Elimination of particles (macrophages) and interaction with lymphocytes
• What are the characteristics of the spleen?

  Size: 7-14 cm in lenth

  Role : eliminates aged red blood cells and thrombocytes , purifies the blood