Immunity

• antigens


  proteins on the cell surface membrane which allow the immune system to detect pathogens, abnormal body cells, toxins and cells from other organisms of the same species
• Phagocytes


  type of white blood cell that destroys pathogens
• Phagocytosis


  -phagocyte attracted to foreign antigen as it moves down its conc gradient towards it (chemotaxis)

  -phagocyte engulfs pathogen

  -phagosome forms around the pathogen

  -lysosomes in the cell migrate towards pathogen

  -lysosomes fuse to phagosome and release hydrolytic enzymes into the phagosome

  -hydrolytic enzymes hydrolyse pathogen

  -products are displayed on the cell surface membrane forming an A.P.C
• cell-mediated response

  -T-helper cell activated by complementary antigen on A.P.C

  -activated t-helper cell divides rapidly by mitosis

  -cloned t-helper cells differentiate into cytotoxic t-cells or activate b-lymphocytes
• Cytotoxic T cells

  causes cell death by injecting perforin into the cell membrane, this creates a pore and allows substances to move into and out of the cell uncontrollably
• Humoural response

  -B-lymphocytes activated by t-cells

  -activated b-lymphocyte divides rapidly by mitosis (clonal selection)

  -differentiate into plasma cells or memory cells

  -plasma cells produce antibodies, memory cells stay in the blood stream
• Antibody structure

  quaternary structure

  4 polypeptides

  2 heavy long chains

  2 light short chains

  
  

  antigen binding site forms antigen-antibody complexes

  variable regions determined by amino acid sequence

  
• Agglutination


  clumping together of multiple antigen-antibody complexes to allow phagocytosis of multiple pathogens at once
• HIV


  retrovirus that is transmitted through the exchange of bodily fluids
• HIV replication

  -HIV enters bloodstream

  -attachment proteins of HIV attach to CD4 on t-helper cell

  -HIV fuses with host cell and releases RNA and reverse transcriptase into the cell

  -reverse transcriptase converts RNA --> DNA

  -Viral DNA moves into host cells nucleus and chromosomes

  -Host cell synthesises proteins using viral DNA

  -HIV particles produced until the cell bursts and releases -HIV particles into the blood
• How does HIV lead to AIDS?

  -HIV replication destroys t-cells, which decreases the body's immune responds as there is a decreased amount of t-cells

  -person is highly vulnerable to infection from opportunistic pathogens (tuberculosis, pneumonia)
• Active immunity


  immunity provided by the body producing its own antibodies against a particular antigen; results from exposure to the antigen via infection or vaccine
• Helper T-cell


  A type of T cell that, when activated, secretes cytokines that promote the response of B cells (humoral response) and cytotoxic T cells (cell-mediated response) to antigens.
• Herd immunity


  When the majority of the population are immune, those not immune are less likely to get infected
• Monoclonal antibodies


  Identical antibodies that have been produced by an immune cell that has been cloned from a parent cell.
• Passive immunity


  A form of immunity provided by the introduction of antibodies to a disease into the body.
• Primary immune response

  Immune response the first time the body is exposed to a particular antigen.
• Secondary immune response

  Immune response after the body has already been exposed to a specific antigen. Response is faster, of greater magnitude, and more prolonged.
• Vaccine

  A harmless variant or derivative of a pathogen that stimulates a host's immune system to produce defenses against the pathogen