immunity

• Physical barriers to infection include:

  • Skin: a tough physical barrier consisting of keratin
  • Stomach Acid (hydrochloric acid) which kills bacteria
  • Gut and skin flora: natural bacterial flora competes with pathogens for food and space
• Non-specific responses to infection:

  • Inflammation: histamines released by damaged white vessels cause vasodilation, increasing blood flow to the infected area and permeability of blood vessels, allowing antibodies, white blood cells, and plasma to destroy the pathogen
  • Lysozyme action: an enzyme found in secretions like tears and mucus that kills bacterial cells by damaging their cell wall
  • Interferon: prevents viruses from spreading to uninfected cells by stopping protein synthesis in viruses
  • Phagocytosis: specialized white blood cells engulf pathogens, destroying them by fusing a pathogen enclosed in a phagocytic vacuole with a lysosome; main phagocytes are macrophages and neutrophils
• After a pathogen is engulfed and destroyed, its chemical markers called antigens are presented on the surface of the phagocyte, becoming an antigen-presenting cell which activates other types of the immune system; immune response is stimulated if the antigen is recognized as foreign
• The specific immune response is antigen-specific and produces responses specific to one type of pathogen only, relying on lymphocytes produced in the bone marrow:

  • B cells mature in the bone marrow and are involved in the humoral response
  • T cells move from the bone marrow to the thymus gland where they mature, involved in the cell-mediated response
• Primary immune response:

  • When the body encounters a pathogen for the first time, the immune system initiates antibody production to destroy the pathogen
  • T and B memory cell production is initiated for a secondary immune response if the same antigen is encountered again
• T lymphocytes:

  • T helper cells stimulate B cells and T killer cells to divide
  • T killer cells destroy pathogen-infected cells
• B lymphocytes:

  • B effector cells form clones of plasma cells
  • Plasma cells produce a large amount of antibodies specific to a foreign antigen
• Memory cells replicate themselves when exposed to an invading pathogen, remaining in the lymph nodes to search for the same antigen, resulting in a faster immune response and long-term immunity
• Antibodies:

  • Structure: Y-shaped glycoproteins that bind to specific antigens to trigger an immune response, with 2 long identical polypeptide chains and 2 shorter identical chains held in place by disulfide bridges
  • Antibodies bind to antigens via a 'lock and key' mechanism, with 2 antigen-binding sites allowing binding to 2 antigens
• Monoclonal antibody production via the hybridoma method:

  • Inject mouse with antigen to produce antibodies specific to the antigen
  • Remove spleen cells producing lymphocytes that produce antibodies
  • Spleen cells bind with myeloma cells to produce hybridoma cells that can continuously divide to produce many antibodies specific to the original antigen
• Monoclonal antibodies can be used in the treatment of diseases like cancer, identifying and treating cancerous cells by clumping together markers present on their surface
• Immunity can be active or passive:

  • Active immunity results from the immune system producing antibodies in response to an antigen
  • Passive immunity results from the introduction of antibodies from another person or animal
• Vaccinations provide long-term immunity, prevent epidemics by stopping disease spread, and contribute to herd immunity when a significant portion of the population is vaccinated