Immune Systems

• Lymphocytes identify pathogens that are foreign and kill them by detecting the proteins on the molecules tertiary structure (antigens)
• Antigen variability is the ability of an antigen to change shape and become recognised by a different antibody due to DNA mutation, making previous immunity ineffective
• Phagocytes are macrophages found in the blood and tissue performing phagocytosis, a non-specific response
• Phagocytosis Process

  • Chemicals, debris or abnormal cells attract phagocytes
  • The receptor binding points attach to foreign objects
  • Phagocytes tertiary structure changes shape and engulfs the pathogen
  • It contains it in a phagosome vesicle
  • Lysosomes fuse with the phagosome and release enzymes (lytic) which hydrolyse the pathogen
• T-Lymphocytes are the most common type of white blood cell, they are responsible for the immune response
• T-Lymphocytes are made in the bone marrow, and mature in the thymus gland
• Antigen Presenting Cells can be infected body cells, macorphages, transplant cells or cancers
• Cell Mediated Response

  • Once engulfed, antigens are presented
  • Helper T Cells attach receptors to the antigens
  • Activates mitosis to replicate and make clones
  • Clones differentiate: some activate B lymphocytes, some stimulate macrophages for phagocytosis, some become memory cells
• Cytotoxic T Cells destroy infected cells, release protein perforin which embeds into cell membrane and makes a pore, granzyme A enters and poisons, B catalyses enters and kills the cell
• B Lymphocytes are white blood cells with specific response made and matured in the bone marrow
• Antigens collide with complemetary antibodies, B cells take antigen via endocytosis and presents on the membrane
• B Cells collide with T Cells which stimulate clonal expansion, undergoing mitosis, differentiating into plasma cells or memory B cells
• Plasma cells make antibodies
• B Memory Cells rapidly divide into plasma cells when re-infected, and can live for decades creating active immunity
• Antibodies are a quaternary structure protein with 2 light and 1 heavy chain with antigen binding sites, they are flexible to bind to many antigens (agglutination)
• Passive Immunity is recieving antibodies from an external source e.g. breast milk
• Active Immunity is exposure to pathogen creating Memory B Cells and Plasma Cells
• Artificial Active Immunity is introducing weakened pathogens in a vaccine
• Herd Immunity is when a large proportion of a population is vaccinated, so that the pathogen cannot spread easily