adaptive immune system

• Immune response


  • Innate
  • Adaptive
• Adaptive (specific) immunity


  • Specificity for particular foreign molecules (antigens = antibody generators)
  • Memory for most previously encountered antigens, so that the second encounter stimulates a faster and greater response
• Adaptive immunity


  • Cell-mediated
  • Antibody-mediated
• Processing and presentation of exogenous antigens on MHC-II

  By an antigen presenting cell (eg macrophage or dendritic cell)
• Activation of naïve helper T-cells in the lymph nodes

  1. By antigens presented on MHC-II by macrophages and dendritic cells

  2. Proliferation and differentiation under the influence of IL-2 induces a clone of daughter cells all able to recognise the same antigen
• Processing and presentation of endogenous (eg viral) antigen on MHC-I

  By an infected body cell
• Activation of naïve CD8 cytotoxic T-cells in the lymph node

  1. By specific antigen presented on MHC-I

  2. Proliferation and differentiation generates a clone of cells all able to recognise the same antigen
• Activated cytotoxic T-cells recognise and bind to infected cells


  1. Perforin causes lysis of the infected cell and granulysin kills the microbe

  2. Granzymes induce apoptosis of the target cell
• 1. cells can be activated


  1. By direct recognition of antigen through B-cell receptors or through T-helper cell activation

  2. Activated B-cells undergo clonal expansion to become antibody producing plasma cells
• Antibody structure


  • V; variable domain
  • C; constant domain
• Antibody classes and functions

  • IgG; A monomer, most abundant antibody in the blood, neutralises bacterial and viral toxins, enhances phagocytosis, and activates complement. Crosses the placenta-fetal immunity.
  • IgA; A dimer, most abundant antibody in sweat, tears, saliva, mucus, milk, protects mucus membranes against adhesion of virus and bacteria.
  • IgM; A pentamer and first antibody to be secreted by plasma cells following activation. Activates complement, causes agglutination and lysis of bacteria. Antibodies to blood group antigens are IgM.
  • IgE; a monomer, mostly found on mast cells in tissue and involved in allergic reactions and defence against parasites.
  • IgD; a monomer, found on the surface of B-cells as an antigen receptor.
• Immunological memory


  • Thousands of memory cells exist after initial encounter with an antigen
  • With the next appearance of the same antigen, memory cells can proliferate and differentiate within hours
  • Serum IgG antibody titers are much higher and much faster on the second response
• The basis for vaccination is immunological memory
• Tortora and Derrickson; Principles of Anatomy and Physiology Chapter 22; Lymphatic system and immunity