Immunological Memory

 

  • During the initial several days following the injection of an antigen in an individual that was not previously exposed to the antigen, no antibodies are detectable (lag period).
  • Antibody production would then rise over time to peak and then to decline, ultimately approaching the baseline. This initial production of antibody is called the primary response. The initial response is mainly due to IgM with IgG appearing later.
  • If an individual has previously made an immune response to a given antigen, a subsequent exposure to that antigen results in a much more rapid rise in antibody to a more prolonged, higher level .
  • The ability to make a secondary response is absolutely dependent on prior exposure to the antigen in question - it is thus an antigen specific phenomenon. In essence the individual has IMMUNOLOGICAL MEMORYof that antigen. This memory may last for periods of years for some immunogens up to decades for others.
  • during the primary immune response the immunogen "selects" from the pool, those cells which recognize it and activates them to undergo proliferation and begin synthesizing antibodies. Due to the relatively low number of cells specific for any given antigen, this process takes some time to get going, (the lag period). The activated cells undergo a limited number of doublings and then cease proliferating and synthesizing antibodies. By the end of this primary response a significant increase in the number of lymphocytes capable of recognizing the inducing antigen have been produced -MEMORY CELLS.
  • Because of the larger number of cells, the chances of early encounters with subsequent "challenges" by the antigen are greatly enhanced resulting in significant shortening of the lag phase. Additionally, the increased number of responding cells results in much higher levels of antibody being attained with subsequent challenges.