imunno

• Components of the immune system

  • Organs/Tissues
  • Connections
  • Cells
• Organs of the immune system

  • Primary/Central lymphoid organs
  • Secondary/Peripheral lymphoid organs
• Primary/Central lymphoid organs


  Provide appropriate microenvironments for the development and maturation of lymphocytes

  
• Primary/Central lymphoid organs


  • Bone marrow
  • Thymus
• Secondary/Peripheral lymphoid organs


  Provide sites for mature lymphocytes to interact with foreign antigens
• Secondary/Peripheral lymphoid organs


  • Lymph nodes
  • Spleen
  • Mucosal-associated lymphoid tissues (Tonsils, Adenoids, Peyer's Patches)

  
• Bone marrow


  • Site of hematopoiesis (generation of all blood cells)
  • At birth, hematopoiesis takes place mainly in the bones throughout the skeleton
  • By puberty, hematopoiesis occurs mostly in the vertebrae, iliac bones, and ribs

  
• Types of bone marrow

  • Medulla ossium rubra (red marrow)
  • Medulla ossium flava (yellow marrow)

  
• Medulla ossium rubra (red marrow)

  Consists mainly of hematopoietic tissue, gives rise to red blood cells, white blood cells and platelets, found mainly in the flat bones

  
• Medulla ossium flava (yellow marrow)


  Mainly made up of fat cells, found in the medullary cavity of long bones, can be converted back to red marrow to increase blood cell production

  
• Hematopoietic Stem Cells (HSCs)


  • Pluripotent, self-renewing

  
• Thymus


  • Bilobed organ present above the heart
  • Each lobe is divided into many lobules separated by fibrous septae
  • Consists of an outer cortex (densely populated with immature T-lymphocytes) and an inner medulla (sparsely populated with Thymocytes)
  • Contains a stromal-cell network of epithelial cells, macrophages, and dendritic cells that contribute to T-cell differentiation and maturation
  • Thymic epithelial cells in the outer cortex (nurse cells) surround and support thymocytes

  
• T lymphocyte differentiation in the thymus

  1. Stem cell (CD3- TCR- CD4- CD8-)

  2. Thymic Cortex (CD3+ TCR+ CD4+ CD8+)

  3. Thymic medulla (CD3+ TCR+ CD4+ OR CD3+ TCR+ CD8+)

  
• The thymus never disappears, but thymic T cell output is reduced and maintained at lower levels throughout life
• Humans with DiGeorge syndrome suffer from T-cell deficiency because of mutations in genes required for thymus development
• Lymph nodes


  • Small, encapsulated, vascularized organs strategically placed along the lymphatic routes
  • Divided into 3 regions: cortex, paracortex, and medulla
  • Cortex contains lymphocytes, macrophages, and follicular dendritic cells
  • Paracortex is populated largely by T lymphocytes and interdigitating dendritic cells
  • Medulla mainly contains plasma cells secreting antibodies
  • Surrounded by a fibrous capsule penetrated by afferent lymphatic vessels
  • Efferent lymphatic vessels merge into the thoracic duct and right lymphatic duct, emptying into the bloodstream

  
• Antigen processing and presentation in lymph nodes

  1. Antigen is carried into a regional node by lymph, trapped, processed, and presented by interdigitating dendritic cells in the paracortex, resulting in the activation of TH cells

  2. Cellular interactions between follicular dendritic cells, B cells, and TH cells in the primary follicles lead to the development of secondary follicles with germinal centers

  3. TH cells migrate to the primary follicles of the cortex

  4. Some B cells within the foci differentiate into plasma cells secreting IgM and IgG antibodies
• Spleen


  • The largest single secondary lymphoid organ in mammals
  • Situated high in the abdomen under the diaphragm on the left side
  • Functions to remove aging and damaged blood cells from the circulation and initiate adaptive immune responses to blood-borne antigens
  • Surrounded by a capsule that extends projections (trabecula) to form a compartmentalized structure
  • Consists of a red pulp (network of sinusoids) and a white pulp (T and B cell areas separated by the marginal zone)

  
• Marginal zone of the spleen

  • Populated by B cells and macrophages, the first line of defense against blood-borne pathogens

  
• Antigen processing and antibody production in the spleen

  Antigen activated B cells and antibodies cross from the white pulp through the marginal zone into the red pulp sinuses, where they are collected by veins leaving the spleen
• Mucosal-associated lymphoid tissue (MALT)

  • Adenoids in the upper airways
  • Tonsils in the throat
  • Peyer's patches and lamina propria of the small intestine

  
• Lymphoid organs are connected to each other and to infected tissue by two different circulatory systems: Blood and Lymphatics