antibodies

• antigens and antibodies

  antigens stimulate production of antibodies

  • almost any molecule can act as an antigen but they are usually proteins or glycoproteins in the plasma membrane of pathogen
  • antibodies are specific so antigen
  • antibodies are immunoglobulins - complex proteins produced by plasma membrane in immune system

  →released as a response to infection

  • they have a region with a specific shape that is complementary to that of a particular antigen
  • our immune system must manufacture one type of antibody for every antigen that is detected

  →antigens attach to antigens + render them harmless
• The structure of an antibody

  antibody molecules are Y-shaped + have two distinct regions

  • consists of 4 polypeptide chains
• how antibodies work

  Opsonins

  • opsonins are a group of antibodies that bind to the antigens on a pathogen

  → they act as binding sites for phagocytic cells, so that these can more easily bind + destroy pathogen

  • some opsonins are not very specific + stick to types of molecules that are not found in the host cell e.g. peptidoglycans found in cell walls of bacteria
• opsonins 2

  • other opsonins are produced as part of the specifc immune response + bind to very specific antigens

  →the pathogen may have another use for this antigen molecule

  e.g it may be a binding site used for attachment to the host cell.

  • in this case, opsonin bound to the antigen renders the antigen useless - a process called known as neutralisation
  • opsonin assists in phagocytosis , but also prevents the pathogen entering the a host cell before it can be attacked by phagocytes
• structure of antibody

  
• Agglutinins

  • Agglutinins causes pathogens to stick together

  → because each antibody molecule has two identical binding sites it is able to ‘crosslink’ pathogens by binding an antigen on one pathogen with one binding site and then an antigen on another pathogen with its other binding site
• Agglutinins

  • when many antibodies perform this crosslinking they clump together (agglutinate) pathogens
  • this has two advantages :
  • the agglutinated pathogens pathogens are physically impeded from carrying out some functions, such as entering host cells, and the agglutinated pathogens are readily engulfed by phagocytes

  →This is particularly effective against viruses
• Anti-toxins

  • some antibodies bind to molecules that are released by pathogenic cells

  →these molecules may be toxic + the action of anti-toxins renders them harmless
• Primary and secondary responses

  when an infecting agent is first detected, the immune system starts to produce antibodies but it takes a few days before the number of antibodies in the blood rises to a level that can combat the infection successfully

  →known as the primary immune response
• Primary response

  1. Pathogens are dealt with

  2. The number of antibodies in blood drops rapidly
• Secondary response

  1. The body is infected a second time by the same pathogen

  2. B and T memory cells recognise the specific antigens

  3. The immune system swings into action more quickly

  4. Production of antibodies starts sooner and is much more rapid

  5. The concentration of antibodies rises sooner and reaches a higher concentration
• The secondary immune response is usually quick enough to prevent any symptoms being detected by the host
• The specific immune system