Immune System - adaptive

• Innate immunity

  Non-specific, Elements present at birth, Effective against a wide range of pathogens, Lifelong presence, Present in all animal species
• Adaptive immunity

  Specific for certain antigens, Gained after exposure to foreign material, Delay before effective - 5-6 days to respond, Memory - faster response to subsequent exposure to same pathogen, Carried out by Lymphatic system, Only in vertebrates, Once acquired, it is lifelong (mostly)
• Innate immune cells

  • Innate Lymphoid Cells (ILCs)
  • Natural Killer Cells (NK)
  • Mast Cells
  • Eosinophils
  • Neutrophils
  • Macrophages
  • Dendritic Cells
• Adaptive immune cells

  • Professional Antigen Presenting Cells (APCs)
  • CD4+ T Helper Cell
  • CD8+ Cytotoxic T cell
  • B Cell
• Lymphocytes are the effector cells of the adaptive immune response
• Lymphocytes

  1. Lymphocytes, B-Lymphocytes, 6 micrometres diameter, Short life span (3 days -8 weeks), Circulate in blood and lymph, Activated by antigen, Both originate in bone marrow
• How immune cells find one another in the body

  Circulation, Lymphatics
• Blood composition

  Blood Volume 8.5 - 9.1% of total body weight, Innate No./μL blood % of WBC, All White Blood Cells 4000 to 11000 100%, Monocytes 200 to 800 5-10%, Neutrophils 2000 to 7500 50-70%, Eosinophils 40 to 400 1-10%, Basophils 10 to 100 <1%, Innate Lymphoid Cells (+NK cells) 1 to 4 (100-500) <1% (2-10%), Lymphocytes 1500 to 4000 20-30%
• Innate immune cells

  • Neutrophil, Eosinophil, ILCs, Basophil, Monocytes
• Adaptive immune cells

  • T-Lymphocytes, B-Lymphocytes
• Once you've defeated a pathogen, you remember it
• Primary lymphoid organs

  Bone marrow - Origin of B and T cells, Thymus - Precursor T cells leave bone marrow and mature in thymus
• Lymphocytes are made in primary lymphoid organs
• How immune cells find pathogens & each other

  1. Interstitial fluid bathes tissue and along with blood cells enters lymphatic vessels

  2. Lymph flows through lymphatic vessels throughout body

  3. Within LNs pathogens and particles in the lymph encounter & activate APCs

  4. Lymphatic vessels return lymph to the blood via two large ducts that drain into veins
• Secondary lymphoid organs

  • Lymph nodes - B cells, macrophages, dendritic cells, T cells and dendritic cells, Antibody secreting Plasma B cells and macrophages
  • Spleen - Blood filter, Germinal centre - Proliferating B lymphocytes, White pulp - B + T cells, macrophages, Red pulp - Old/dead RBC removed, Macrophages, Lymphocytes, Plasma cells (antibody production)
• Cells that activate the adaptive immune response

  • Dendritic cells, Macrophages, B cells
• Humoral immunity

  1. cell/antibody-mediated, Antibodies defend against pathogens (bacteria and viruses) and toxins in extracellular fluid
• Cell-mediated immunity

  Cytotoxic T cell mediated, CD8+ CTL defend against infected cells, cancer cells and transplanted cells
• Antigen

  Any foreign molecule which is specifically recognised by lymphocytes and elicits a response from them, EPITOPE = ANTIGENIC DETERMINANT
• B and T cell receptors

  B and T cells have receptors embedded in their plasma membranes, Each B or T cell is specific for ONE antigen epitope, Antibody diversity possible > 10^10
• B cell activation - The humoral response

  Developing B cells undergo a selection process in bone marrow: self-reactive cells are destroyed, Mature B-cells released from bone marrow, Memory B-cell, Receptor interacts directly with pathogen, Affinity maturation, MATURE ACTIVATED Plasma B-cell, ANTIBODIES
• Antibody structure

  Typical Y shaped representation of an antibody molecule, The B cell Receptor (BCR) is a membrane bound antibody, Heavy chains, S-S bridges, Antigen Binding Sites, Light chains
• Antibody subclasses

  • IgM - First Ig to be formed after antigen exposure, Pentameric
  • IgE - Allergic reactions
  • IgD - Membrane bound
  • IgA - In secretions, J-chain
  • IgG - Highest amounts
• Secondary response to antigen is faster, greater and of increased duration
• Lymph nodes filter Lymph & The Spleen filters blood
• Adaptive immune responses are both humoral and cell mediated
• Antigens are foreign molecules recognised by lymphocytes
• BCRs and TCRs are specific for only one antigen
• There are 5 subclasses of antibody
• Second exposure to an antigen results in a faster, greater, longer immune response
• Effector cells of the adaptive immune response

  • T-Lymphocytes, B-Lymphocytes, T-helper cells, Cytotoxic T-cells
• T cell surface proteins

  • CD4, CD8, CD4+, CD8+, Th1, Th2, Th17, Treg
• T cell development

  Developing T cells undergo two selection processes, positive then negative selection, T cell receptor, CD4+CD8+ T cells express a range of proteins on their surface, CD4+, CD8+, DP, DN, Cell Death (Cells that do not recognise self MHC), Cell Death (cells that recognise self too strongly), Mature T-cells
• T cell activation

  CTL activated by presented antigen from infected cell, Infected cell, CD8, TCR, MHC-I, Antigen, Active Cytotoxic T cells (CTL), Memory Cytotoxic T cells (CTL), T H cell activated by antigen presented by Antigen Presenting Cell, CD4, Bug (gets phagocytosed), Antigen, TCR, MHC-II, Active T H cells, Memory T H cells
• Cytotoxic T cells express CD8, T helper cells express CD4
• Infected cells present antigen on MHC-I to Cytotoxic CD8 T cells
• Antigen presenting cells present processed antigen on MHC-II to CD4 T cells
• Thymus & BM = Primary Lymphoid Organs, LN + Spleen = Secondary Lymphoid Organs
• B cells make antibodies, T lymphocytes can be CTLs or T H
• second exposure on antibodies

  1. first exposure to antigen A
  2. primary response to antigen A produces antibodies to A
  3. day 28: second exposure to antigen A: first exposure to antigen B
  4. secondary response to antigen A produces antibodies to A: primary response to antigen B produces antibodies to B