Primary and secondary immune responses

The presence of a foreign antigen stimulates the production of a exact antibody in the bloodstream which will recognize and bind tightly to it. Antibody molecules fall into 5 major classes their responses as described through their precise structure. The antibody  molecules  first produced  after antigen  injection  are  in  the  immunoglobulin   M  class  and  so  are  called  IgM  molecules. Moreover about 10 days after antigen injection the amount of IgM in the blood- stream  the  titer  of  antibody  declines  and  there  is  a  concurrent  increase  in another  class  of  antibody  known as  immunoglobulin   G  (IgG) which is described in Figure.  This is called the primary immune response.

One  of the very  important  features  of the immune  system  is that, the  system  confers  protection once  an animal  has  encountered  a  particular  pathogen,  against  future  infection.

                     Figure: The primary and secondary immune responses to injections of antigen.

This  immunological  memory  denote  that if the similar antigen  or pathogen is encountered  a second time possibly  even decades  after the past occurrence  then the system reacts much faster and more dramatically to produce  a huge titer of specific  IgG to counter  the antigen.  This is the secondary immune response and is mediated through long-lived memory B cells and memory T cells.