5.5 - Antibodies

• what are antibodies?


  proteins called immunoglobulin mode by plasma calls with specific binding sites that destroy specific antigens
• how do antibodies destroy antigens?

  cause agglutination of pathogens forming clumps so it's easier for phagocytes to find them

  then they serve as markers to stimulate phagocytes to engulf cells to which they are attached
• how agglutinins inactivate antigens


  cause antigens to bind together forming inactivated
• how antitoxins inactivate antigens


  bind to toxins & neutralise them
• how opsonin's inactivate antigens

  tags foreign cells for destruction by phagocytes
• what are antibodies made of?

  4 polypeptide chains - 1 pair of long, heavy chains & 1 pair short, light chains
• structure of antibodies - constant regions

  same for all antibodies Of the same class

  they bind to receptors on cells
• Structure of antibodies - variable regions

  forms the antigen binding sites that's different on different antibodies
• structure of antibodies - antigen binding sites

  each antibody has 2 so can bind to a pathogens at once

  antibody recognises epitopes on antigen and binds to it forming an antigen- antibody complex
• Structure of antibodies - hinge region

  connects light and heavy chains through disulfide bonds so the two chains can open and close
• what are monoclonal antibodies

  antibodies artificially produced that are all genetically identical so bind to & destroy one specific antigen
• uses of monoclonal antibodies

  pregnancy tests

  medical diagnosis

  preventing rejection in organ transplants

  targeting medication to specific cells
• meaning of monoclonal antibodies


  mono: single/one

  clonal: genetically identical
• Why aren't blymphocytes used to make monoclonal antibodies


  if you take them out of the body they won't divide well
• Making monoclonal antibodies


  Mouse exposed to non-self material corresponding to antibody needed

  b-lymphocytes in mouse produce a mixture of antibodies which are extracted from the spleen of the mouse

  b-lymphocytes are fused with myelomas (cancer cells) to form hybridomas

  hybridomas are separated under a Microscope & each cell is cultured from a clone

  clones producing antibodies needed are grown on a large scale I antibodies are extracted from growth Medium

  antibodies undergo humanisation
• who developed monoclonal antibodies?

  Cesar Milstein and George Kohler
• what does ELISA stand for?

  enzyme linked immunosorbent assay
• What's ELISA used for?

  to detect an antigen in a sample of liquid using monoclonal antibodies
• types of ELISA


  direct ELISA: uses one antibody complementary to antigen

  indirect ELISA: uses 2 different antibodies
• how ELISA works

  liquid containing suspected antigen is placed into a well, of a plastic plate & left to adhere to plastic so becomes immobilised

  complementary monoclonal antibody with enzyme tag is added to wells

  plastic plate is washed so unbound antibody-enzyme molecules are washed away

  substrate to enzyme is added which reacts to produce a colour change

  intensity of colour indicates the quantity of antigen
• controls in ELISA test

  positive control

  negative control
• positive control in ELISA

  contains antigen

  if it doesn't change colour the test isn't working
• negative control in ELISA test

  doesn't contain antigen

  if it changes colour it suggests contamination
• what do pregnancy tests detect

  HCG - human chorionic gonadotropin
• how do pregnancy tests work?

  application area contains mobile monoclonal antibodies with enzyme attached

  When urine goes on application area HCG binds to antibodies forming antigen-antibody complex

  mobile antibodies move up the stick by capillary action

  test strip contains immobile monoclonal anti-HCG antibodies with the substrate attached

  mobile HCG complex binds to antibodies on test strip & enzyme -substrate reaction creates a coloured line

  in control strip there are immobile secondary antibodies that detect anti-HCG antibody & enzyme substrate complex generates a coloured line
• what are monoclonal antibodies are used to detect

  influenza

  hepatitis

  chlamydia

  some cancers

  HIV
• diagnosing prostate cancer


  Men with prostate canur often produce more of PSA protein

  by using monoclonal antibodies we can obtain a measure of the level Of PSA in the blood
• targeting drugs to cancer cells

  cancer calls have antigens called tumour markers that aren't Found on normal body cells

  monoclonal antibodies that bind to tumour markers so block chemical signals that stimulate cell growth
• indirect Monoclonal antibody therapy

  radioactive or cytotoxic drug is attached to monoclonal antibodies

  monoclonal antibodies bind to turnour Markers so release drug straight to cancer cells
• side effects of using monalonal antibodies to treat cancer

  they're reduced because anti-cancer drug only accumulates on cancer cell so no damage done to healthy cells
• Why are monoclonal antibodies called magic bullets?

  they only hill cancer cells

  used in smaller doses - cheaper & reduces side effects
• What's herceptin

  a Monoclonal antibody that attaches to HER2 receptor proteins on cells to help T cells target them for destruction to treat breast cancer
• HER2 protein


  produced by HER2 gene which is overexpressed by cancerous cells so they divide too much
• how herceptin destroys cancer cells

  herceptin recognises HER2 protein & attaches to it

  t-lymphocytes recognise antibody as foreign & attack destroying the cell I reducing tumour
• What monoclonal antibody is used to prevent rejection in organ transplant

  OKT3
• how does OKT3 work

  it specifically binds to CD3 receptor on t lymphocytes so it no longer forms complexes with t lymphocyte receptor so it can no longer identify antigens so transplanted organ is safe from immune system

  t-lymphocytes are still produced but don't have CD3 receptor
• ethical issues regarding monoclonal antibodies

  animal testing

  human safety when used in treatments

  genetic engineering-human genes transplanted into mine for humanisation

  testing on humans