7.3

• Two types of immunity:

  • antibody-mediated immunity (humoral response) - provided by B-cells which involves producing antibodies
  • cell-mediated immunity - provided by T-cells which involves forming specialised cells that destroys pathogens
• Lymphocytes are made in the bone marrow, T-cells mature in the thymus and B-cells mature in bone marrow.
• Antigen:

  • substance triggering an immune response
  • causes the body to produce antibodies
  • self-antigen - large molecules produced in the body that do not cause an immune response
  • non-self antigen - foreign compounds triggering an immune response
• Antibody:

  • Y-shaped specialised protein
  • produced by plasma cells in response to a non-self antigen
  • classes - IgA, lgD, IgE, IgG, IgM
• Antigen-antibody complex:

  • antigen molecules have specific active sites
  • antibody has the complementary shape
• Antigen-presenting cells:

  (dendritic cells, macrophages, undifferentiated B-cells)

  • detects presence of non-self antigen and engulfs it
  • digests the pathogen → small fragments produced
  • fragments moves to cell surface → presents antigen to lymphocytes
• Primary response:

  (immune reaction of first exposure to an antigen)

  • takes several days to build up large amounts of antibodies
  • B-cells takes time to multiply and differentiate
  • leaves immune system with memory of the antigen
• Subsequent exposure:

  • memory cells recognises antigen more quickly → faster response
  • plasma cells formed very quickly
  • antigen has little opportunity to exert any noticeable effect
• How antibodies work:

  • inactivate foreign enzymes/toxins by combining with them or inhibiting their reaction
  • binds to the surface of viruses and prevents entry
  • coats bacteria for easier consumption
  • agglutination - clumping of bacteria, viruses or foreign blood cells
  • dissolves organisms
  • reacts with soluble substances → becomes insoluble and more easily consumed
• Antibody-mediated immunity:

  (secretion of antibodies into the blood and lymph)

  • provides resistance to viruses, bacteria and bacterial toxins before its entry into the body
  • APC digests pathogens and displays the antigen on their surface and presents it to lymphocytes in lymphoid tissue
  • APC stimulates helper T-cells and B-cells
  • plasma cells from B-cells produces antibodies and releases them into blood and lymph
• B-cells:

  • has different receptors
  • B-cells activated → enlarge and divide into a clone
  • most clones becomes plasma cells secreting complementary antibodies
  • antibodies circulate in blood, lymph and extracellular fluid to reach invasion site
• Memory cells:

  • made of remaining B- and T- cells of the clone
  • allows a more rapid response in the future
• Cell-mediated immunity:

  • provides resistance to intracellular phase of infection
  • T-lymphocytes responds to only one particular antigen
  • foreign antigen + APC = T-cells activated/sensitised
  • T-cell enlarge and divide into clones
  • either differentiates into a killer T-cell or memory cell
• Types of T-cells:

  • killer T-cells - attaches to invading cells and secretes a chemical to destroy the antigen
  • helper T-cells - binds to antigen/APC → stimulates cytokine secretion
  • cytokine - proteins released in response to antigens and acts as messengers in immune response
  • attracts lymphocytes and macrophages
  • promotes actions of macrophages and killer T-cells
  • suppressor T-cells - slows down immune response by inhibiting T- and B- cell activity
• natural and passive - antibodies enter via placenta/milk

  natural and active - able to manufacture antibodies from attack of a disease

  artificial and passive - antibodies injected into bloodstream

  artificial and active - able to manufacture antibodies by gaining antigen via vaccination
• cell-mediated immunity:

  works against transplanted tissues/organs, cancerous/infected cells and provides resistance to fungi and parasites