Introduction Antibodies and antigens interact in order to trap the offending microbe generate an immune reponse in secondary lymphoid organs Kinetics of antigen-antibody interaction antigen excess seen in the start of the infection due to pathogen proliferation antibody production has not yet started equivalence antibody production has become adequate and thus free antibody or antigen cannot be detected this corresponds to the window period for heptitis B antigen serologic studies antibody excess the infection has resolved and thus there is more antibody than antigen